The effect of addition of ceria on 
platinum supported on carbon materials 
in the hydrogenation of ethylene 
 
 
By 
 
Audacity Maringa 
 
A dissertation submitted to the Faculty of Science, University of the 
Witwatersrand, Johannesburg, in fulfillment for the degree of Master of Science. 
 
Supervisors: Professor M.S. Scurrell 
     Professor N.J. Coville 
 
 
June, 2011 
ii | P a g e  
 
DECLARATION 
 
I declare that this dissertation, which  I submit for the Degree of Master of Science in the 
University of the Witwatersrand, Johannesburg, is apart from the recognized assistance of my 
supervisor, Professor M.S Scurrell, my own work. It has not been submitted before for any 
degree, diploma or examination in any other institution. 
 
________________             On this ___________ day of ______________ 2010 
  (Candidate)  
________________             On this ___________ day of ______________ 2010 
  (Supervisor)   
 
 
 
 
 
 
 
 
 
 
 
iii | P a g e  
 
DEDICATION 
 
I dedicate this work to my beloved one, Josphine, my parents, my sisters (Alice, Nyaradzo and 
Polite)  and brother Peter. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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ACKNOWLEDGEMENTS 
 
I would like to thank the following people and organizations for their support and assistance 
towards the success of this project: 
 
xrhombus Professor M.S Scurrell, Professor N.J Coville for their outstanding supervision during the 
course of this study 
 
xrhombus Dr Amit Deshmukh for guidance and support during the course of the project 
 
xrhombus The CATOMAT group for company and the support that you provided 
 
 
xrhombus The Microscopy and Microanalysis Unit for the microscopy analysis 
 
xrhombus The University of the Witwatersrand and National Research Foundation (NRF) PGM 
Flagship for the financial support. 
 
 
xrhombus Special thanks to my beloved one, Josphine, and my family for their support 
 
xrhombus Finally I thank Jehovah for making it possible  
 
 
v | P a g e  
 
PRESENTATIONS AND PUBLICATIONS 
 
Oral presentations 
Audacity Maringa, Michael S. Scurrell, Neil J. Coville, The effect of ceria addition onto 
platinum supported on carbon materials in the hydrogenation of ethylene. PGM seminar,  
University of Western Cape, Cape Town, South Africa, September 2010. 
Poster presentations 
Audacity Maringa, Michael S. Scurrell, Neil J. Coville, The effect of ceria addition onto 
platinum supported on carbon materials, Cross Faculty Symposium, University of the 
Witwatersrand, Johannesburg, South Africa, October 2010. 
Audacity Maringa, Michael S. Scurrell, Neil J. Coville, The effect of ceria addition onto 
platinum supported on carbon materials. South African Chemical Institute (SACI), University of 
the Witwatersrand, Johannesburg, South Africa, February 2011. 
Attendances 
? PGM seminar, University of Western Cape, Cape Town, South Africa, July 2009. 
? CATSA conference, Cape Town, South Africa, November 2009 
? South African Nanotechnology Initiative (SANI), Nanoscience Young Researcher 
Symposium (NYRS), University of Johannesburg, Johannesburg, South Africa, May 
2010. 
? SACI Young Chemists Symposium, North West University, Potchefstroom, South 
Africa, October 2010 
Publications 
Audacity Maringa, Michael S. Scurrell, Deshmukh Amit, Neil J. Coville, Hydrogenation of 
ethylene using Pt-CeO2/C catalysts. (To be submitted) 
 
 
vi | P a g e  
 
ABSTRACT 
 
This study reports the synthesis of carbon materials (carbon nanotubes (CNTs), coiled carbon 
nanofibers (CCNFs) and carbon spheres (CSs)) using the chemical vapour deposition (CVD) 
method. The as-synthesized carbon materials were functionalized using nitric acid in order to 
introduce functional groups and improve the hydrophilic behavior of the carbon materials. Both 
the as-synthesized and functionalized carbon materials were characterized by TEM, TGA, 
Raman and FTIR spectroscopy. The presence of functional groups was confirmed by alkalimetry 
titration and IR spectroscopy data. Ceria (synthesized using the sol-gel method), activated carbon 
(AC) and titania (P25) were other catalysts supports used and their morphologies were 
determined by TEM. 
 Platinum was deposited on the various supports to give Pt loadings of 0.5, 1 and 5 % using the 
polyol method. It was found that small Pt particle sizes were obtained with average particle sizes 
of 1.8, 2.3, 2.6, 2.9, 2.7 and 1.6 nm for Pt/CCNF, Pt/CNT, Pt/CS, Pt/AC, Pt/CeO2 and Pt/TiO2 
respectively at 0.5 % Pt loading. Pt was also deposited on the CeO2/CM supports (5 % and 10 % 
CeO2 loadings) to make Pt-CeO2/CM catalysts. The Pt supported catalysts were characterized by 
TEM, EDS, XRD, TPR, BET and TGA. 
The platinum supported catalysts were tested for the hydrogenation of ethylene. The effect of 
functionalization of the carbon materials was determined. Pt/functionalized carbon materials had 
better activity than Pt/as-synthesized carbon materials. On the effects of supports; Pt/TiO2 
showed the best activity compared to Pt/CCNF, Pt/CNT, Pt/CS, Pt/AC, Pt/CeO2 and this was 
attributed to the small Pt sizes formed on TiO2 (Pt mean size was 1.6 nm). An interesting feature 
in this study was the higher activity of the Pt-CeO2/CM as compared to Pt/CM. This was due to 
the effect of ceria in preserving the surface area of Pt by suppressing sintering. The effect of 
increasing the ratio of hydrogen to ethylene was investigated and the findings indicated that all 
the ethylene was converted to ethane. This was attributed to the fact that at a high hydrogen 
concentration, the rate of formation of the carbon deposit is slow and the rate of hydrogenation is 
high. No carbon deposits are thus expected on the Pt catalyst particles. It was found that an 
increase in the Pt loading resulted in an increase in the rate of reaction.  
vii | P a g e  
 
TABLE OF CONTENTS  
 
 
Declaration 
Dedication 
Acknowledgement 
Presentations and publications 
Abstract 
Table of content 
List of figures 
List of tables 
List of abbreviation 
Page number 
ii 
iii 
iv 
v 
vi 
vii 
xii 
xv 
xvi 
CHAPTER ONE 
INTRODUCTION 
1 
1 
1.1 
1.2 
1.3 
1.4 
Background 
Motivation 
Objectives of the project 
Outline of the dissertation 
1 
2 
3 
4 
CHAPTER TWO 
LITERATURE REVIEW 
7 
7 
2.1 
2.2 
2.2.1 
2.2.2 
2.3 
2.3.1 
2.3.2 
Introduction 
Unsupported catalysts 
Raney nickel 
Adams? catalyst 
Supported catalysts 
Role of support 
Desirable characteristic of a support 
7 
7 
8 
9 
9 
9 
10 
viii | P a g e  
 
2.3.3 
2.4 
2.4.1 
2.4.2 
2.4.3 
2.4.4 
2.4.5 
2.5 
2.5.1 
2.5.2 
2.6 
2.7 
2.7.1 
2.7.2 
2.7.3 
2.7.4 
2.7.5 
2.7.6 
2.7.7 
2.7.8 
2.8.0 
2.8.1 
2.8.2 
2.9.0 
2.9.1 
2.9.2 
2.9.3 
2.10 
2.11 
Why supported catalysts? 
Carbon supports for hydrogenation reactions 
Carbon nanotubes 
Carbon nanofibers 
Carbon spheres 
Carbon helices 
Activated carbon 
Metal oxides as support 
Ceria 
Titania 
Combination of ceria and carbon materials 
Preparation methods for supported catalysts 
Low temperature chemical precipitation 
Deposition precipitation 
Colloidal methods 
Sol-Gel method 
Impregnation 
Microemulsions  
Electrochemical deposition 
Microwave heating 
Hydrogenation of ethylene 
Why hydrogenate ethylene 
 Studies undertaken using ethylene hydrogenation 
Mechanism of ethylene hydrogenation 
Horiuti-Polanyi mechanism 
Twigg mechanism 
Jenkins-Rideal mechanism 
Hydrogen adsorption and surface migration 
Summary 
10 
10 
11 
13 
15 
16 
17 
18 
18 
20 
20 
21 
21 
21 
22 
22 
23 
23 
24 
25 
25 
26 
26 
27 
27 
28 
29 
29 
31 
 
ix | P a g e  
 
CHAPTER THREE 
EXPERIMENTAL METHODS 
37 
37 
3.1 
3.2 
3.3 
3.3.1 
3.3.2 
3.3.3 
3.3.4 
3.3.5 
3.3.6 
3.3.7 
3.4 
3.4.1 
3.5 
3.6 
3.6.1 
3.6.2 
3.6.3 
3.7 
3.7.1 
3.7.2 
3.7.3 
3.7.4 
3.7.5 
3.7.6 
3.7.7 
3.7.8 
3.7.9 
Introduction 
Materials and chemicals  
Synthesis of carbon materials 
Catalyst preparation for CNTs 
Synthesis of CNTs 
Catalyst preparation for CCNFs 
Synthesis of CCNFs 
Purification of CCNFs 
Synthesis of carbon spheres 
Summary of the carbon materials synthesis procedures 
Functionalization of carbon materials 
Oxidation of carbon materials 
Synthesis of ceria 
Synthesis of the supported platinum catalyst 
Synthesis of platinum supported on carbon materials  
Synthesis of platinum supported on oxides 
Synthesis of Pt-CeO2/CM 
Characterization techniques used in this study 
Transmission electron microscopy 
Thermal gravimetric analysis 
Ultraviolet-Visible spectrophotometry 
Raman spectroscopy 
Temperature programmed reduction 
X-ray diffraction 
Brunauer-Emmett-Teller N2 adsorption (Surface area) 
Fourier transform infrared spectroscopy 
Inductively coupled plasma atomic spectra emission spectroscopy 
37 
37 
37 
38 
38 
39 
39 
39 
40 
40 
40 
40 
41 
41 
41 
42 
42 
43 
43 
44 
44 
44 
45 
45 
46 
46 
46 
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3.8 
3.8.1 
 
Hydrogenation reactions 
Experimental set up 
46 
47 
CHAPTER FOUR 
RESULTS AND DISCUSSION 
50 
50 
4.1 
4.2.1 
4.2.1.2 
4.2.1.3 
4.2.1.4 
4.2.1.5 
4.2.1.6 
4.2.1.7 
4.2.2 
4.2.3 
4.3 
4.3.1 
4.3.2 
4.4 
4.4.1 
 
4.4.2 
4.4.3 
4.4.4 
4.5 
4.5.1 
4.6 
4.6.1 
4.6.2 
Introduction 
TEM analysis of the carbon materials  
Purification of CCNFs 
Analysis of the functionalized carbon materials 
Thermal gravimetric analysis of the carbon materials 
Raman spectra of the carbon materials 
Infrared spectroscopy 
 Surface area and pore volume measurements 
Characterization of ceria by TEM 
Characterization of activated carbon and titania by TEM 
Analysis of the Pt supported catalysts 
Mechanism of polyol synthesis 
Formation of Pt: UV-vis spectroscopy 
0.5% Pt loaded catalysts. 
TEM analysis for the 0.5% Pt loaded on to the as-synthesized 
CMs 
TEM analysis for the 0.5% Pt loaded catalysts (polyol method) 
Determination of presence of Pt in the catalyst. 
 Surface area and pore volume measurements of 0.5% Pt catalysts 
1% Pt loaded catalysts 
Microwave versus conventional heating 
5% Pt loaded catalysts 
Effect of loading on the particles size 
Temperature programmed reduction 
50 
50 
51 
52 
56 
58 
60 
62 
62 
63 
64 
64 
65 
65 
66 
 
67 
70 
71 
71 
74 
74 
77 
77 
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4.6.3 
4.6.4 
4.7 
4.7.1 
4.7.2 
4.8 
4.8.1 
4.8.2 
4.8.3 
4.9 
4.9.1 
4.9.2 
4.9.3 
X-ray diffraction studies on Pt supported catalysts 
Particle size from XRD 
Ceria supported on carbon materials 
XRD profile of ceria supported on carbon materials 
Platinum deposited onto CeO2/CM 
Catalytic activity 
Effect of functionalization 
Effect of metal loading  
Effects of increasing the ratio of H2:C2H4  
Effect of catalyst supports 
Effect of adding ceria on the Pt/CM catalyst 
Effect of temperature 
Effect of ceria loading 
80 
82 
83 
84 
85 
87 
87 
90 
91 
91 
93 
94 
95 
 
CHAPTER FIVE 
CONCLUSION AND RECOMMENDATIONS 
99 
99 
5.1 
5.2.1 
5.2.2 
5.2.3 
5.3 
5.4 
5.5 
Introduction 
Carbon materials  
Ceria 
Titania and activated carbon 
Deposition of platinum 
Hydrogenation activities of the Pt supported catalysts 
Recommendations for future work 
99 
99 
100 
100 
100 
101 
102 
 
 
 
 
 
xii | P a g e  
 
LIST OF FIGURES 
 
CHAPTER TWO 
Figure 2.1: 
 
 
Figure 2.2: 
Figure 2.3: 
 
Figure 2.4: 
Figure 2.5: 
Figure 2.6: 
Figure 2.7: 
Figure 2.8: 
Figure 2.9: 
The Raney process, in which a nickel/aluminium alloy is prepared by 
fusion and subsequently the Al is dissolved by NaOH, leaving a Ni 
sponge. 
Image of a MWNT showing different graphene sheets rolled together. 
Schematic representation of different stacking shapes of graphene sheets 
of CNF. P-CNF: platelet carbon nanofibers 
Mechanism of CNF synthesis 
Coiled carbon nanotubes with pentagon-heptagon rings 
Horiuti-Polanyi mechanism for hydrogenation of ethylene 
Twigg mechanism of ethylene hydrogenation 
Possible extremes in hydrogen adsorption 
Removal of carbonaceous deposit by reaction of spillover hydrogen, 
leading to restoration of catalytic site 
 
8 
 
 
12 
14 
 
14 
16 
28 
29 
30 
31 
 
CHAPTER THREE 
Figure 3.1: 
Figure 3.2: 
A schematic CVD setup for carbon material synthesis 
Schematic representation of the hydrogenation reaction set up 
38 
47 
CHAPTER FOUR 
Figure 4.1: 
Figure 4.2: 
 
Figure 4.3: 
Figure 4.4: 
 
TEM images of the as synthesized (a) CCNFs (b) CSs (c) CNTs 
TEM images of the HF treated CCNFs (a) uncoiled fibers and (b) 
coiled fibers 
Different oxygen-containing surface groups on the carbon materials 
TEM image of CCNFs functionalized at 100 oC for 3 h 
 
51 
52 
 
53 
54 
 
xiii | P a g e  
 
Figure 4.5: 
 
Figure 4.6a: 
Figure 4.6b: 
Figure 4.6c: 
Figure 4.7: 
 
Figure 4.8: 
 
 
Figure 4.9: 
Figure 4.10: 
Figure 4.11: 
 
Figure 4.12: 
Figure 4.13: 
Figure 4.14: 
Figure 4.15: 
 
 
Figure 4.16: 
Figure 4.17: 
 
 
 
Figure 4.18: 
 
 
 
Figure 4.19: 
Figure 4.20: 
TEM images of (a) CNTs (b) CCNFs (c) CSs functionalized by reflux 
at 50 oC for 12 h.  
TGA profile of CCNFs before and after purification 
TGA profile of the as-synthesized and functionalized CNTs 
TGA profile of the as-synthesized and functionalized CSs 
Comparison of the Raman spectra of functionalized and as-
 synthesized (a) CCNFs, (b) CNTs and (c) CSs. 
IR spectra of (A) CCNFs , (B) CNTs and (C) CSs with (a) as-
 synthesized (b) functionalized samples are shown in all the three 
figures 
TEM image of ceria 
TEM images of (a) AC and (b) titania 
Schematic representation of the mechanism behind the polyol 
synthesis method  
UV-Vis spectra of Pt  
Pt loaded to the as-synthesized (a) CCNFs, (b) CNTs and (c) CSs 
Filtrates obtained from (a) Pt/CCNF, (b) Pt/CNT and Pt/CS  
TEM images and size distributions of 0.5% Pt supported on (a) and (b) 
CCNF; (c) and (d) CCNF; (e) and (f) CNT; (g) and (h) CS; (i) and (j) 
AC; 
 
(k) and (l) CeO2; (m) and (n) TiO2. 
EDS spectra of Pt/CCNF 
TEM images and size distributions of 1% Pt supported on (a) and (b) 
CCNF prepared by conventional heating and the rest were  prepared 
by microwave heating; (c) and (d) CCNF; (e) and (f) CNT; (g) and (h) 
CS; (i) and (j) AC; 
 
(k) and (l) CeO2; (m) and (n) TiO2 
TEM images and size distributions of 5% Pt supported on (a) and (b) 
CCNFs prepared by conventional heating and the rest were  prepared 
by microwave heating; (c) and (d) CCNFs; (e) and (f) CNTs; (g) and 
(h) CSs; (i) and (j) AC; 
 
(k) and (l) CeO2; (m) and (n) TiO2.  
TPR profile of (a) Pt/CS, (b) Pt/CCNF and (c) Pt/CNT 
TEM image of Pt/CCNF (a) before and (b) after TPR analysis 
55 
 
57 
57 
58 
59 
 
61 
 
 
63 
63 
64 
 
65 
67 
67 
69 
 
 
70 
73 
 
 
 
77 
 
 
 
78 
79 
xiv | P a g e  
 
Figure 4.21: 
Figure 4.22: 
 
Figure 4.23: 
 
Figure 4.24: 
Figure 4.25: 
Figure 4.26: 
 
Figure 4.27: 
 
Figure 4.28: 
Figure 4.29: 
 
Figure 4.30a: 
 
Figure 4.30b: 
 
Figure 4.31: 
 
Figure 4.32: 
Figure 4.33: 
Figure 4.34: 
 
Figure 4.35: 
Figure 4.36: 
Figure 4.37: 
Figure 4.38: 
Figure 4.39: 
H2-TPR profile of Pt/CeO2 and CeO2 
XRD patterns of (a) CCNF and Pt/CCNF, (b) CS and Pt/CS and (c) 
CNT and Pt/CNT 
XRD patterns of (a) AC and Pt/AC, (b) CeO2 and Pt/CeO2 and (c) 
TiO2 and Pt/TiO2 
TEM images of (a) CeO2/CCNF, (b) CeO2/CS and (c) CeO2/CNT 
TGA profile of 5% and 10% loading of ceria on CCNF. 
XRD patterns of (a) CeO2/CCNF, (b) CeO2, (c) CeO2/CNT and (d) 
CeO2/CS 
TEM images of (a) Pt-CeO2/CCNF (b) Pt-CeO2/CNT and (c) Pt-
 CeO2/CS 
EDS spectra of Pt-CeO2/CCNF 
Ethylene conversion over Pt supported on (a) as-synthesized CCNFs 
and (b) functionalized CCNFs at 30 oC 
TEM images of the Pt/as-synthesized CCNFs  (a) before and (b) after 
hydrogenation of ethylene  
TEM images of (a) before and (b) after hydrogenation of ethylene 
using Pt/functionalized CCNF 
Effect of Pt loading on the conversion of ethylene, (a) 0.5%, (b) 1%, 
(c) 5%  
Effects of the supports on the conversion of ethylene.
    
Effect of adding ceria to the Pt/CM catalyst.
   
 
Cartoon showing a possible mechanism for suppression of Pt 
sintering. 
TEM image of Pt-CeO2/CCNF 
Effect of temperature on ethylene conversion over 0.5% Pt/CCNF.  
TEM image of (a) before and (b) after hydrogenation of ethylene 
Effect of ceria loading.  
TEM image of 1% Pt-10% CeO2/CCNF  
 
79 
80 
 
81 
 
83 
84 
85 
 
86 
 
86 
88 
 
88 
 
89 
 
90 
 
92 
93 
94 
 
94 
95 
95 
96 
96 
xv | P a g e  
 
LIST OF TABLES 
 
                                                                                                                               Page number 
CHAPTER THREE 
Table 3.1: Summary of the carbon materials synthesis conditions 
 
40 
CHAPTER FOUR 
Table 4.1a: 
Table 4.1b: 
Table 4.2: 
Table 4.3: 
Table 4.4: 
Table 4.5: 
Table 4.6: 
Table 4.7: 
Table 4.8: 
Table 4.9: 
Table 4.10: 
Table 4.11: 
 
Table 4.12: 
 
Table 4.13: 
 
Yield of CMs remaining after reflux for 3 h at 100 oC  
Yield of CMs remaining after reflux for 12 h at 50 oC  
Estimates of the acid groups on the carbon materials (50 oC/12 h) 
Raman data for as-synthesized and acid-treated CCNF and CNTs 
Surface area and pore volume of the catalyst supports 
Summary table of the mean particle size of catalyst with different Pt loading. 
Pt loading in the catalysts obtained from ICP AES analysis 
Comparison of the results obtained using different heating method  
Summary table of the mean particle size of catalyst with different Pt loading. 
Ceria loading obtained using TGA 
Pt loading in the catalysts 
Conversion rates of the 1% Pt supported for the as-synthesized and 
functionalized CNTs and CSs in 300 mins 
Conversion of ethylene using different loadings of Pt on CNTs and 
CSs 
Effect of increasing flow rate of H2:C2H4. (H2/C2H4 = 5) 
 
53 
53 
56 
60 
62 
70 
71 
74 
82 
84 
87 
89 
 
91 
 
91 
 
 
 
 
xvi | P a g e  
 
LIST OF ABBREVIATIONS 
 
AC:   Activated carbon 
a.u:   Arbitrary unit 
BET:   Brunauer-Emmett-Teller 
ca:   approximately 
CCNF(s):  Coiled carbon nanofiber(s) 
CNT(s):  Carbon nanotube(s) 
CM(s):   Carbon material(s) 
CS(s):   Carbon sphere(s) 
CVD:   Chemical vapor deposition 
DNA:   Deoxyribonucleic acid 
DWNT(s):  Double walled nanotube(s) 
EAS:   Electrochemical active surface 
EDS:   Energy dispersion spectroscopy 
EG:   Ethylene glycol 
f-CNFs:  fishbone carbon nanofibers 
FID:   Flame ionization detector 
FTIR:   Fourier-transform infrared spectroscopy 
g:   Grams 
GC:   Gas chromatography 
h:   Hour 
ICP-AES:  Inductively coupled plasma atomic spectra emission spectroscopy  
ID/IG:    Ratio of the intensity of D- and G-band 
IUPAC:  International Union of Pure and Applied Chemistry  
mEq:   milliequivalent 
mins:   minutes 
mL:   milliliter 
mol:   Mole 
MWNT(s):  Multi walled nanotube(s) 
nm:   Nanometers  
xvii | P a g e  
 
p-CNFs:  platelet carbon nanofibers 
r-CNFs:  ribbonlike carbon nanofibers 
SWNT(s):  Single walled nanotube(s) 
TCD:   Thermal conductivity detector 
TEM:   Transmission electron microscope 
TGA:   Thermal gravimetric analysis 
THF:   Tetrahydrofuran 
TPR:   Temperature programmed reduction 
TWC:   Three way catalyst 
UV-vis:  Ultra violet-visible spectroscopy  
WGS:   Water gas shift 
XRD:   X-ray diffraction 
 
 
 
 
 
 
 
 
 
 
 
 
 
1 | P a g e  
 
CHAPTER ONE 
INTRODUCTION 
 
1.1 Background 
Hydrogenation is the addition of molecular hydrogen to an unsaturated hydrocarbon. 
Unsaturated hydrocarbons possess either double bonds or triple bonds as found in alkenes 
and alkynes respectively. The importance of hydrogenation is seen in the petrochemical 
industry where compounds in crude oil containing multiple bonds are converted to saturated 
compounds before use in gasoline.1 The unsaturated compounds are not wanted because they 
are unstable and burn in air with a smoky flame.2 A typical olefin saturation reaction is 
shown below. 
C6H12 + H2 ? C6H14 
Hydrogenation is also essential in the fine chemicals and pharmaceutical industries, for 
example, in the production of sorbitol from glucose. Sorbitol is a sweetener in ?sugar free? 
food products intended for diabetics  and is used as a starting material for vitamin synthesis.3 
In the food industry hydrogenation is used to convert vegetable oils to margarine .4 A typical 
example is the conversion of oleic acid to stearic acid,5 which is shown below. 
 
CH3(CH2)7CH=CH(CH2)7COOH + H2 ? CH3(CH2)7CH2CH2(CH2)7COOH 
 
Hydrogenation is a process which can be performed by either heterogeneous or homogeneous 
catalysts.6 Heterogeneous catalysis is a two phase reaction in which the catalyst is a solid 
(either a finely divided metal such as platinum, palladium and nickel or supported metals 
such as palladium on activated carbon) and the reactants are gaseous or liquid substances 
(hydrogen gas and an unsaturated hydrocarbon). In homogeneous catalysis, the reaction 
occurs in one phase. Typically organometallic complexes of ruthenium, rhodium and iridium 
are used. In this project, hydrogenation using a novel heterogeneous carbon supported 
catalyst was used. 
Heterogeneous catalysts used for hydrogenation reactions are based on transition metals. 
These are  classified as base metals (Ni, Cu and Co) and platinum group metals (Pt, Pd, Rh, 
2 | P a g e  
 
Ru, Ir).7 The platinum group metals were selected for use over the base metals because they 
are more active and thus require milder conditions and a smaller amounts of catalyst. The 
disadvantage of the platinum group metals is that they are more costly. Platinum was selected 
because of its outstanding ability to catalyze the hydrogenation of alkenes. In contrast with 
palladium, isomerization and double bond migration almost never occur when platinum is 
used.8 
The hydrogenation of ethylene is one of the most common reactions used in organic 
chemistry. It was first studied by Sabatier and Senderens in an effort to understand this 
simple alkene hydrogenation reaction.9 The hydrogenation of ethylene was used to understand 
the mechanism of the reaction with the assumption that the data would apply to more 
complicated alkenes. For example, the principle involved in this reaction was used to 
understand the catalytic hydrogenation of unsaturated vegetable oils used in the production of 
margarine.10 In this project the hydrogenation of ethylene was used as a test reaction to study 
the effect of different catalyst supports on catalytic performance. 
1.2 Motivation 
Platinum is one of the most expensive platinum group metals. The role of platinum is 
attributed to its excellent chemical and physical properties. For instance, its resistance to 
oxidation and its ability to withstand high temperatures in the catalytic converters used in  
cars make Pt very useful.11 In 2006 the platinum demand by application was 50.4% for use as 
an autocatalyst in vehicles.12 It is very important to use such a precious metal very effectively 
and efficiently. Use of unsupported platinum in catalysis is very wasteful as only the outer 
layer will be involved in the reaction and the bulk will not used. Supported platinum will also 
reduce sintering and poisoning of the catalyst. The platinum nanoparticles can be dispersed 
evenly on a support thus increasing the surface area which in turn will increase the rate of the 
reaction. Carbon materials (CMs) come in many morphologies ranging from fullerenes to 
graphenes. In this project the CMs used include carbon nanofibers (CNFs), carbon 
nanospheres (CNSs) and carbon nanotubes (CNTs). CMs have been selected as the support 
because of their unique chemical and physical properties. The properties include their 
inertness and their ability to resist acidic or alkaline conditions. The catalysts used in the 
study will be as denoted as Pt/CM.  
Some examples of the use of Pt or Pd supported on CM have been described in the literature. 
Pt/CNF has been reported to have a better activity when compared to platinum on activated 
3 | P a g e  
 
carbon (Pt/AC) and platinum on alumina (Pt/Al2O3) for the hydrogenation of toluene.13 High 
activity and selectivity were obtained using a 2% Pt/CNT catalyst in the selective 
hydrogenation of citral.14 Functionalized carbon microsphere supported palladium has been 
shown to be effective in the hydrogenation of ethylene.15  
 Despite the good activity of the Pt/CM catalysts, the reports have suggested that sintering is 
a major problem leading to catalyst deactivation. It has been suggested that the addition of 
ceria to a Pt catalyst could reduce sintering.16 Ceria has been reported to be useful in the 
catalytic converters of vehicles where it stabilizes the precious metals (and alumina) against 
sintering and particle growth.17 Pt/ceria has been found effective in the selective 
hydrogenation of ?,? unsaturated aldehydes.18 Combining the beneficial aspects of CMs and 
ceria could yield a good catalyst for hydrogenation reactions. These catalysts are denoted as 
Pt-CeO2/CM. A Pt-CeO2/C catalyst has been studied in the citral hydrogenation reaction.19 
The results indicate that the presence of ceria was beneficial. The beneficial effect is brought 
about by interaction between ceria and Pt, forming a Pt-O-Ce bond which acted as an anchor 
to suppress sintering.16 In this work, further investigations of the beneficial effects of ceria in 
the hydrogenation of ethylene were studied. To fulfil this goal, ceria was added to the 
different Pt/CM catalysts. 
1.3 Objective of the project 
The main aim of this project is to study the effect of the addition of ceria to the Pt/CM catalytic 
system for the hydrogenation of ethylene. The objectives of this study include: 
1. To synthesize carbon materials (CNT, CNS, CNF) using the chemical vapour deposition 
(CVD) method. 
2. To synthesize and characterize platinum supported on the carbon materials. 
3. To synthesize Pt on CeO2/CM, Pt on ceria, Pt on activated carbon and Pt on titania to provide 
comparative data.  
4. To study the hydrogenation of ethylene by varying the active catalysts. 
 
This study will then provide results that will allow for the evaluation of the Pt/CM catalysts as 
potential olefin hydrogenation catalysts. 
 
 
 
4 | P a g e  
 
1.4        Outline of the dissertation  
The outline of the dissertation is given below: 
Chapter 1 (Introduction) ? This Chapter gives an insight, motivation and objectives of 
the study. 
Chapter 2 (Literature review) - A review of the literature pertaining to carbon materials, 
ceria, titania and activated carbon as catalyst support in the hydrogenation reactions is 
given. A brief discussion of the metals involved in hydrogenation reactions is also 
included. 
Chapter 3 (Experimental) - The experimental procedures and all analytical techniques 
that were used in this study are presented and described in this chapter. 
Chapter 4 (Results and discussions) - The results obtained in this study, together with 
their discussion and interpretation are presented in this Chapter. 
Chapter 5 (Conclusions) ? Conclusions are drawn from the results obtained in this 
project. 
 
 
 
 
 
 
 
 
 
 
 
 
 
5 | P a g e  
 
References 
1. http://science.jrank.org/pages/3465/Hydrogenation-Hydrogenation-in-industry.html 
(accessed 15 November 2010) 
2. http://www.faqs.org/faqs/autos/gasoline-faq/part1/ (accessed 15 November 2010) 
3. K. van Gorpa, E. Boermana, C.V. Cavenaghib, P.H. Berbena, Catal. Today 52 (1999) 
349-361 
4. http://www.isco.com/WebProductFiles/Applications/105/Application_Notes/Catalytic
 _Hydrogenation.pdf (accessed 15 November 2010) 
5. http://www.elmhurst.edu/~chm/vchembook/558hydrogenation.html (accessed 15 
November 2010) 
6. Morrison, Boyd, Organic Chemistry, Prentice-Hall International, (1992) 324-325  
7. H. F. Rase, Handbook of Commercial catalysts, CRS press, USA (2000) 108-109 
8. G.Ertl, H. Knozinger, J. Weitkamp, Handbook of heterogeneous catalysis, Wiley, 
Germany, volume 5 (1997) 2192-2193 
9. J. Horiuti and K. Miyahara, Hydrogenation of Ethylene on Metallic Catalysts, 
NSRDS-NBS, (1968) 13-14 
10. http://www.tutorvista.com/chemistry/hydrogenation-of-ethene  (accessed 15 
November 2010) 
11. http://www.chemistryexplained.com/elements/L-P/Platinum.html (accessed 15 
November 2010) 
12. http://www.unctad.org/infocomm/anglais/platinum/uses.htm (accessed 15 November 
2010) 
13. M. Zhou, G. Lin, H. Zhang, Chin. J. Catal. 28 (2007) 210-211 
14. E. Asedegbega-Nieto, A. Guerrero-Ruiz, I. Rodriguez-Ramos, Carbon 44 (2006) 804-
 805 
15. K. C. Mondal, L. M. Cele, M. J. Witcomb, N. J. Coville, Catal. Commun. 9       
(2008) 494?498 
16. H. Shinjoh, M. Hatanaka, Y. Nagai, T. Tanabe, N. Takahashi, T. Yoshida, Y. Miyake, 
Top Catal. 52 (2009) 1967?1971 
17. A.F. Diwell, R.R. Rajaram, H.A. Shaw, T.J. Truex, Studies in Surface Science and 
Catalysis, 71 (1991) 139-152 
18. J. Silvestre-Albero, F. Rodriguez-Reinoso, A. Sepulveda-Escribano, J. Catal. 210 
(2002) 127-128 
6 | P a g e  
 
19. J. C. Serrano-Ruiz, A. Sepulveda-Escribano, F. Rodriguez-Reinoso, D. Duprez, J. 
Mol. Catal. A: Chem. 268 (2007) 227-234 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
7 | P a g e  
 
CHAPTER TWO 
LITERATURE REVIEW 
2.1  Introduction 
This chapter focuses on the literature associated with solid catalyst involved in hydrogenation 
reactions. Solid catalysts can be classified as either unsupported catalysts or impregnated (or 
supported) catalysts. The different supports used for hydrogenation activities will be 
discussed. The chapter will conclude with literature associated with the hydrogenation of 
ethylene. 
Heterogeneous catalysts used for hydrogenation reactions are mostly based on transition 
metals. These are  classified as base metals (Ni, Cu and Co) and platinum group metals (Pt, 
Pd, Rh, Ru, Ir).1 The platinum group metals are more active as compared to the base metals 
and require milder conditions and smaller amounts of catalyst as compared to the base  
metals. The disadvantage of the platinum group metals is that they are more costly and for 
that reason they are usually supported to reduce the amount of precious metal used. Platinum 
metal was selected in this dissertation study because of its outstanding ability to catalyze the 
hydrogenation of alkenes. In contrast with palladium, isomerization and double bond 
migration in olefins almost never occurs when platinum is used.2 
Homogeneous catalysts used for hydrogenation reactions are mainly based on the organic 
complexes of ruthenium, rhodium and iridium. Their mechanism of reaction involves 
forming active complexes with the reactants that are unstable. The unstable complexes will 
breakdown to form the product and reform the catalyst. The major drawback of homogeneous 
catalysts is that they are difficult to separate from the products (and reactants). For this reason 
heterogeneous catalysts are preferred because of the ease to separate them from the product.  
2.2 Unsupported catalysts 
Unsupported catalysts are typically made by precipitation, hydrothermal synthesis and fusion. 
They can be (mixed) metals or oxides and, as their name suggests, the entire catalyst is made 
of active materials. Raney nickel and Adams? catalyst fall into this category and both are 
active in the hydrogenation of hydrocarbons. 
 
8 | P a g e  
 
2.2.1  Raney nickel 
Raney nickel was discovered by an American engineer Murray Raney in 1925.3 He 
discovered that metal alloy leaching gave a superior hydrogenation catalyst when compared 
to unleached metal. He made a 50:50 Ni/Al alloy by fusion and then leached out Al with 
aqueous NaOH. The resulting Ni sponge is the Raney nickel. The synthetic process is shown 
in Figure 2.1. The advantage of the catalyst is that it is ready for use, requiring no reduction 
or other activation and has a high surface area. The disadvantage of the catalyst is that high 
temperature is required for fusion, it is pyrophoric (will ignite instantaneously in air) and 
therefore it has to be stored under water. It is also a health hazard since acute exposure to 
Raney Ni may causes irritation of the respiratory tract, nasal cavities and it also causes 
pulmonary fibrosis if inhaled.4 Apart from safety concerns, a Raney Ni catalyst can have a 
slower of rate of reaction and requires high temperatures when compared to the platinum 
group metal catalysts.5 
 
 
 
 
 
 
 
 
 
Figure 2.1 The Raney process, in which a nickel/aluminium alloy is prepared by fusion and 
subsequently the Al is dissolved by NaOH, leaving a Ni sponge.6 
An example of a reaction catalyzed by Raney Ni is the conversion of benzene to cyclohexane. 
The reaction is a liquid phase reaction which occurs at a temperature between 200 - 225 oC 
and pressure of 50 bar. Li and Xu.7 have shown that silica-supported Ni?P amorphous 
catalysts had a higher activity than the Raney Ni catalyst. Liu et al, 8 also cited the lower 
efficiency and environmental pollution caused by Raney Ni and proposed the use of Ni/CNF 
(CNF=carbon nanofiber) as an alternative catalyst. A Ni/CNF catalyst presents high activity 
Ni 
Al 
Fusion at high 
temperature 
Ni/Al alloy Ni sponge 
(Raney Ni) 
- Al(OH)3 
NaOH 
9 | P a g e  
 
in the liquid phase benzene hydrogenation to cyclohexane, and gives 99.5% yield of 
cyclohexane.  In other words a supported catalyst would be preferred to an unsupported 
catalyst. 
2.2.2 Adams? catalyst 
Adam?s catalyst is made of platinum oxide (PtO2). Adams? catalyst was discovered by 
Voorhees and Adams.9 It was prepared by fusion of chloroplatinic acid (H2PtCl6) or 
ammonium chloroplatinate [(NH4)2PtCl6] and sodium nitrate. In the process platinum nitrate 
is heated to remove nitrogen oxides leaving behind platinum oxide. The equations for the 
synthesis of PtO2 are shown below. 
H2PtCl6 (aq) + 6 NaNO3 (aq) ? Pt(NO3)4 (s) + 6 NaCl (aq) + 2 HNO3 (aq) 
 
Pt(NO3)4 (s) ? PtO2 (s) + 4 NO2 (g) + O2 (g) 
An advantage of using the Adams? catalyst is that it is easy to prepare. Brown et al,10 
investigated the hydrogenation of cyclohexene using PtO2, unsupported Pt and supported Pt. 
They discovered that the platinum catalyst produced by borohydride reaction caused the 
absorption of hydrogen to proceed at nearly twice the rate observed with the commercial 
Adams? catalyst. The supported platinum showed the best activity, an activity 3-4 times that 
of an unsupported catalyst.  
2.3 Supported catalysts 
Supported catalysts are commonly used in the case of precious metals or unstable 
compounds. Here, the active metal precursor is deposited on a porous support. The support 
can be an oxide (e.g. silica, titania, alumina, ceria and magnesia), or a carbon (activated 
carbon, carbon nanotubes, carbon spheres and carbon nanofibers). A supported catalyst 
facilitates the flow of gases through the reactants and diffusion of reactants through the pores 
to the active phase to enhance the selectivity, retarding the sintering of the active phase and 
increasing the poison resistance of the metal.11 
2.3.1 Role of support 
The basic role of the support is to maintain the catalytically active phase in a highly dispersed 
state, stabilization of the active component and enlargement of the specific surface area.12 
10 | P a g e  
 
The role of the support is not limited to being a carrier, and it can also contribute to the 
catalytic activity and can react to some extent with other catalyst ingredients during the 
manufacturing process. The support can also play a crucial role in terms of providing either 
acidity or basicity to the reaction. 
2.3.2 Desirable characteristic of a support 
1. The support material should be inert towards the chemical reaction. The advantage is 
that it will not interfere with the reaction, but it can affect the shape selectivity due to 
the pore arrangement. Thus, the effect of addition of a promoter may be studied 
without interference from the support. 
2. Adequate structural properties to allow the transport of gases through the support 
structure. 
3. High surface area and a well-developed porosity are very important for achieving a 
high dispersion of the active phase in the catalyst.13 
4. Stability of the support at high temperature. 
2.3.3 Why supported catalysts? 
? Costs. The active components for a catalytic reaction are often expensive metals (e.g. 
Pt, Ru, Rh and Re) and through dispersion the cost of catalyst can be minimized. 
? Activity. A supported catalyst has a comparable activity to that of unsupported 
catalyst, which leads to fast reaction rates, short reaction times and maximum 
throughput, elimination of side products and lowering of purification costs. 
? Selectivity. Supported catalysts have a high selectivity towards the desired product. 
This means they facilitate generation of a maximum yield of a desired product. 
? Regenerability helps to keep process costs low. 
2.4 Carbon supports for hydrogenation reactions 
Carbon materials have been used for a long time in heterogeneous catalysis, because they can 
act as direct catalysts or more importantly they can satisfy most of the desirable properties 
required for a catalyst support.11 Carbon materials are good as catalyst supports owing to 
their specific properties: they are stable in both acid and basic media, and the carbon can be  
burnt off, allowing an economic and ecological recovery of the precious catalytic metal.14 
11 | P a g e  
 
The interaction of the active phase with the support (carbon) can be modified by pretreatment 
of the support. However carbon materials cannot be used in reactions that are carried out 
under the following conditions: hydrogenation at temperatures higher than 427 oC (methane 
will be formed) or oxidation above 227 oC (carbon dioxide will be given off).13  
The carbon materials can exhibit a range of different pore sizes (micro, meso, and macro) and 
pore distributions. According to IUPAC, micropores are smaller than 2 nm, mesopores are in 
the range between 2 and 50 nm, and macropores are larger than 50 nm. The different pores 
have different effects on catalytic reactions.13 Micropores show strong adsorption for small 
molecules. The mesopores allows access of reactants to the active phase of a catalyst. The 
macropores are useful for the transport of molecules between the liquid phase and the 
mesopores. Several studies have reported that for liquid-phase hydrogenation reaction, the 
use of CNT and CNF supports possessing large mesoporosity provides better catalytic 
activities than an activated carbon, for which mass-transfer limitations are in operation.13  
Mesoporous carbon spheres has been reported to exhibit a high specific activity compared to 
the monodisperse carbon spheres.15 
2.4.1 Carbon nanotubes 
The discovery of fullerene in 1985 by the Smalley research group at Rice University 
stimulated the research into other forms of carbon.16 In 1991 a Japanese scientist Ijima 
studied the carbons formed by an arc discharge process under a TEM. His findings of carbon 
nanotubes led to an explosion of other studies in the area.17 Carbon nanotubes (CNTs) can be 
thought of as narrow strips of graphene rolled up into seamless tubes.18 CNTs are allotropes 
of carbon with a cylindrical nanostructure. 
CNTs are  classified as single walled nanotubes (SWNTs), double walled nanotubes 
(DWNTs) and multi walled nanotubes (MWNTs) depending on the number of rolled up 
graphene layers that they possess. A typical MWNT is shown in Figure 2.2.19 
 
 
Figure 2.2. Image of a MWNT showing different graphene sheets rolled together.
  
There are various methods used to synthesize CNTs. The major methods used are arc 
discharge, laser ablation and chemical vapour deposition (CVD) methods. Arc discharge is 
the simplest method used to produce CNTs. It involves breaking down the reactant cont
 carbon by an electric current between two graphite electrodes. A disadvantage is that it is 
difficult to separate the CNTs
 crude product.20 Laser ablation involves the laser vaporization of graphite rods e.g. with a 
50:50 catalyst mixture of cobalt and nickel at 1200
 include difficulties in purifying and scaling up the CNT production.
 deposition (CVD) of hydrocarbons over a metal catalyst is a classical method that has been 
used for many decades to produce various carbon materials such as carbon fibers and 
filaments. Large amounts of 
acetylene over nickel, cobalt and iron
 carbonate and titania. The method is considered t
 synthesis of high quality CNTs using gaseous or liquid hydrocarbons as carbon source. The 
mechanism of synthesis involves decomposition of the carbon source, followed by 
dissolution of the carbon phase into me
 on the catalytic surface.21  
 
CNTs have been used to support metals in hydrogenation reaction. A 1
 catalyst deposited on CNTs was found to be active for the hydrogenation of nitrobenze
 yield of 90 % aniline was obtained. 
effective catalysts for the hydrogenation of benzene at room temperature.
 were found to be active for a cyclooctene  hydrogenation reaction.
 reported the hydrogenation of  benzene and its derivative at room temperature using a 
 
 from the soot and the residual catalytic metals present i
  ?C in flowing argon. Its drawbacks 
20
 CNTs can be formed by catalytic CVD of, for example, 
 catalysts supported on silica, alumina, calcium 
o be a low cost, large scale procedure for the 
tal catalytic nanoparticles and redeposition of carbon 
 
Pt, Rh and Pt-Rh particles supported by CNTs were 
23
 13
  Pan and 
12 | P a g e  
19
  
aining 
n the 
 Chemical vapour 
% (w/w) platinum 
ne.22 A 
 Pd/CNT catalysts 
Wai24 have 
13 | P a g e  
 
Rh/CNT catalyst. CNTs supported on palladium catalysts have been reported for the selective 
hydrogenation of cinnamaldehyde at atmospheric pressure. Ge et al25 have reported that the 
Pd/CNT catalyst has a good conversion of 92 % for cinnamaldehyde and 90.8 % selectivity 
of cinnamaldehyde to hydrocinnamaldehyde. Ju et al26 have found that depositing a NiP 
amorphous alloy on CNTs can improve catalytic activity, which is attributed to the dispersion 
produced by the support, an electron donating effect and the hydrogen storage ability of 
CNTs. Pt/CNT showed a higher activity in comparison to Pt/AC in the hydrogenation of 
trans-stilbene.27 The advantage of Pt/CNT was in avoiding the effect of the diffusion of the 
reactant and product molecules in the micropores. Yan et al28 have reported a high catalytic 
performance of a Pt-Sn-B/CNT catalyst in the liquid phase hydrogenation of 
chloronitrobenzene. The conversion of chloronitrobenzene could reach 99.9 % and the 
dechlorination of chloroaniline was less than 1.9 %. 
2.4.2 Carbon nanofibers 
The history of graphitic carbon nanofibers (CNFs) goes back more than a century. The first 
patent describing the production of carbon filaments was published in 1889.29 The fibers were 
often formed by metal-based catalysts used for the conversion of carbon-containing gases, 
such as in Fischer-Tropsch syntheses or steam reforming reactions. Their occurrence was 
considered a nuisance. In the 1980s researchers realised the potentials of the CNFs30 as 
unique materials suitable for various applications. 
There are three main types of CNFs,31 which differ in the alignment of the graphene layers: 
In ribbonlike CNFs (r-CNFs) the graphene layers are parallel to the growth axis. Platelet 
CNFs (p-CNFs) display graphene layers perpendicular to the growth axis, while herringbone 
or fishbone CNFs (f-CNFs) have layers stacked obliquely with respect to the growth axis. 
The schematic diagram for the three types of CNF are shown in Figure 2.3.32 In general CNFs 
have a larger diameter than those presented by CNTs.13 
14 | P a g e  
 
 
Figure 2.3. Schematic representation of different stacking shapes of graphene sheets of CNF. P-CNF: 
platelet carbon nanofibers; r-CNF: ribbon-like carbon nanofibers; f-CNF: fishbone carbon 
nanofibers32 
The methods of synthesizing the CNFs are similar to those used in CNT synthesis, which 
include arc discharge, laser ablation and chemical vapour decomposition (CVD). Owing to 
the low cost and ease of large scale production of CNFs, the CVD method is preferred over 
other methods. The mechanism of CNF synthesis is shown in Figure 2.4. 
 
 
 
 
 
 
 
Figure 2.4. Mechanism of CNF synthesis. The first step is the decomposition of carbon-containing 
gases on the metal surface, followed by carbon atoms dissolving in and diffusing through the bulk of 
the metal. Lastly the precipitation of carbon in the form of a CNF occurs  
 
CNFs have been used as a catalyst support in a number of reactions. Ni and Pd particles 
supported by CNFs have shown an excellent selective hydrogenation capacity for 
crotonaldehyde33to crotyl alcohol and cinnamaldehyde34 to cinnamyl alcohol. Rh 
Carbon source 
Metal particle 
H2/CO2/H2O 
Carbon nanofibers 
15 | P a g e  
 
nanoparticles on CNFs are highly active in the liquid-phase hydrogenation of cyclohexene.35 
Liang et al36 have reported that Pd/CNF has a high activity and stability in the hydrogenation 
of cyclooctene, presumably as a result of a special metal-support interaction and absence of 
micropores. Liu et al8 have reported the high activity of Ni/CNF in the liquid phase 
hydrogenation of benzene to cyclohexane. The high activity was attributed to the effective 
surface area, the skeletal structure and the metallic and semi-conductive properties of the 
CNFs. Among the different types of CNFs supporting platinum, p-CNFs were found to be the 
best support in the hydrogenation of nitroarenes to aromatic amines.37 The efficiency of the  
Pt/p-CNF was attributed to the steric and the electronic effects derived from the interaction 
between Pt nanoparticles and the p-CNF support. Similar results were obtained by Motoyama 
and co-workers.38 they showed that p-CNF was more effective as a support in comparison to 
other types of CNFs. They used ruthenium in their investigation and they concluded that the 
Ru/p-CNF catalyst was highly active and reusable for arene hydrogenation reactions.  Toebes 
et al39 studied the effect of the different concentrations of oxygen-containing surface groups 
on the CNF support for the hydrogenation of cinnamaldehyde. They found that the activity 
was strongly dependent on the amount of oxygen in/on the CNF support. The as synthesized 
Ni/CNF catalysts have been reported to show a very good activity and selectivity for the 
hydrogenation of chloronitrobenzene to the corresponding chloroanilines.40 
2.4.3 Carbon spheres 
The discovery of fullerenes in 1985 stimulated research effort into carbon materials. This 
included studies on the well known carbon spheres. Carbon spheres (CSs) have always 
attracted a lot of attention due to their unique properties and applications.41 Carbon spheres 
have similar properties to graphite or fullerene, and they have been used to fabricate diamond 
films, lubricating materials and special rubber additives.42 Carbon spheres can be used as 
electrodes, as a support for catalysts, capsules for magnetic nanoparticles, a template for 
synthesizing other hollow materials and for the delivery of drugs. Carbon spheres can be 
hollow or solid. 
 
Carbon spheres can be synthesized using various methods which include chemical vapour 
deposition, arc plasma techniques, catalyzed reduction and hydrothermal synthesis. Chemical 
vapour deposition can occur in the presence or absence of a catalyst. Carbon spheres have 
been obtained by pyrolysis of acetylene at temperature between 900 oC and 1000 oC.43 This 
16 | P a g e  
 
method does not require a catalyst hence there is no catalyst removal step required. In the 
hydrothermal synthesis method the carbon source is heated in an autoclave.44 Owing to the 
advantageous properties of carbon spheres as catalyst supports, several studies have been 
carried out on different catalytic reactions. Co45 and Pd46 nanoparticles supported on carbon 
spheres have shown high activity for the conversion of ethylene to ethane. Ni/CS catalysts 
were found to be active in the gas phase hydrogenation of nitrobenzene with aniline formed 
as the sole product.47 
2.4.4 Carbon helices 
Helical carbon materials such as carbon micro-coils or nano-coils have a relatively long 
history and have received increasing attention in recent years.48 Great efforts have recently 
been made to study single carbon nanofibers49 and nanotubes50 because of their coiled 
morphologies and potential applications. Some of the applications for the carbon helices 
include nano-scale mechanical springs and electrical inductors.50 Carbon helices are also 
ideal candidates for electromagnetic wave adsorbent tunable micro-devices, bioactivators, Li 
battery electrodes and hydrogen containers.51 Nano-coils are also interesting in that helices 
abound in nature e.g. DNA, proteins, etc., and a connection can be made at the nano-scale 
between carbon based inorganic and organic structures.52 For application of coils it is 
necessary to have control over the coil morphology and geometry, which to date has not been 
adequately achieved. It has been proposed that while the curvature in the case of helically 
coiled single walled nanotubes could possibly be due to the regular insertion of pentagon-
 heptagon pairs at the junction, it is however unclear whether a similar mechanism could hold 
for multi-walled nanotubes. Figure 2.5 shows a coiled carbon nanotube with pentagon-
 heptagon rings.53  
 
Figure 2.5. Coiled carbon nanotubes with pentagon-heptagon rings.53 
17 | P a g e  
 
CVD has been used to synthesize the helical carbon materials. By varying the experimental 
conditions it was established that it is possible to produce carbon nanostructures with 
significant structure differences such as straight, curved or helical morphologies. For 
example, coiled nanocoils with a twisted form can be grown from the Ni/Al2O3 catalysed 
pyrolysis of acetylene.54 
 
Not much is known about helical carbon materials as catalyst supports. Li and Zhang55 have 
reported the use of helical nano-coiled and micro-coiled carbon fibers as catalyst supports for 
the electrooxidation of methanol. They concluded that the platinum supported on the helical 
nano-coiled and micro-coiled carbon fibers exhibited superior electrocatalytic activity and 
anti-poisoning ability relative to the straight fibers. The use of helical carbon nanofibers as 
catalyst supports for the hydrogenation reactions is an area of interest as it has not been 
studied to date. 
2.4.5 Activated carbon 
Activated carbon (AC) is also known as activated charcoal and it refers to the type of carbon 
formed from a carbon source which is processed with oxygen in order to increase the number 
of pores in the product.56 The highly porous carbon materials with high surface area are used 
to absorb other substances for example the impurities  in sugar57. The surface area for an 
activated carbon is at least 500 m2g-1. 
For the production of activated charcoal, carbon sources (wood, charcoal, peat, lignite, coal 
and petroleum pitch) are used as the precursors or raw materials. The methodology used for 
the synthesis of activated charcoal involves either physical reactivation or chemical 
activation. In the former type, the raw material is activated by using specific gases, whereas 
in the latter case, the precursor is impregnated with certain chemicals (strong salt, base or 
acid), which is then carbonized at a lower temperature.56 One of the limiting factors in                 
chemical activation is the retention of the impregnated substances in the activated carbon 
product. Chemical activation is preferred over physical activation owing to the lower 
temperatures and shorter time needed to activate the carbon. 
AC has been used as a support for metal catalysts for a very long time. A 2.4 % Pt/AC has 
been reported to have a toluene conversion of 55 % to give methylcyclohexane.58 Jiang et 
al,59 showed that platinum catalysts supported on activated carbon with high purity, large 
18 | P a g e  
 
surface area, large pore volume and appropriate pore structure exhibited a high activity for 
the hydrogenation of ortho-nitrochlorobenzene to 2,2?-dichlorohydrazobenzene. Palladium 
supported catalysts on AC have been used to study the selective hydrogenation of 
cinnamaldehyde.60 Cabiac et al60, reported the presence of hydrocinnamaldehyde and that 
there was no sign of cinnamyl alcohol formation in the reaction. 
2.5 Metal oxides as support 
The conventional supports for hydrogenation catalysts include titania, silica, alumina and 
ceria. These supports have different morphologies and structures. Their influence on the 
hydrogenation activity varies depending on how they interact with the active phase. Only 
ceria and titania are discussed below. Ceria will be discussed since its effect on addition to 
the Pt/C systems is the one that will be examined in this dissertation. Titania was selected in 
order to compare the carbon supports with a conventional support. 
2.5.1 Ceria 
Ceria is an oxide of cerium and cerium is the most abundant of the rare earth elements. It is a 
pale yellow powder with chemical formula CeO2. CeO2 is stable at room temperature and 
atmospheric pressure. It can maintain its structure under intensive reduction at elevated 
temperatures. Ceria in the fluorite structure exhibits several defects depending on the partial 
pressure of oxygen. The defect structure is an intrinsic property required for its potential in 
catalysis, energy conversion etc.61 
 
There are various methods used to prepare cerium oxide particles, such as by precipitation, 
hydrothermal, sol-gel and microemulsion procedures.62 The sol-gel method has the advantage 
in that the ceria produced has the following attributes: purity, homogeneity and controlled 
porosity combined with an ability to form a large surface area at low temperatures.63 
 
Monyanon et al64 prepared ceria using a sol-gel method. Cerium nitrate was used as the 
source of ceria and urea as a precipitating agent. The mechanism of reaction is as follows: 
Urea in solution hydrolyses to give hydroxyl ions. Cerium nitrate reacts with hydroxyl ions to 
give cerium (III) hydroxide. In the presence of atmospheric oxygen, cerium (III) hydroxide is 
19 | P a g e  
 
oxidized to cerium (IV) hydroxide. The cerium (IV) hydroxide is dehydrated to give cerium 
(IV) oxide (ceria). The chemical equations for ceria formation are shown below: 
CO(NH2)2 (aq) + 3H2O (l)? CO2 (g) +2NH4+ (aq) + 2OH- (aq) 
Ce(NO3)3.6H2O (aq) + 3NH4+ (aq) + 3OH- ? Ce(OH)3 (s) + 3NH4NO3 (aq) + 6H2O (l) 
Ce(OH)3 (s) + O2 (g) + 2H2O (l) ? 4Ce(OH)4 (s) 
Ce(OH)4 -nH2O (s)? CeO2.xH2O (l) + yH2O (where x + y = n) 
Ceria has unique properties which include high mechanical strength, oxygen ion conductivity 
and oxygen storage capacity.65 It is used in fuel cells, optical films, polishing materials, gas 
sensors, promoting precious metals in the water gas shift (WGS) reaction and it is a crucial 
component of automotive, three way, emissions-control catalysts.66 The role of ceria in the 
three way catalyst (TWCs) of automotives is very attractive and important in utilising 
efficiently precious metals. Ceria is suggested to: 67  
? Promote the noble metal dispersion 
? Increase the thermal stability of the Al2O3  
? Promote water gas shift and steam reformation reactions 
? Favour catalytic activity at the interfacial metal-support sites 
? Promote CO removal through oxidation employing lattice oxygen 
? Store and release oxygen under lean and rich conditions respectively 
 
Ceria is a good catalyst support. Phenol has been hydrogenated to cyclohexanone at 180 oC 
and under atmospheric pressure on 3 % Pd/CeO2 and phenol conversion was 80 % (in which 
about 50 % was cyclohexanone, 35 % cyclohexanol and 15 % cyclohexane).68 For the 
conversion of propionitrile to n-proplyamine, a copper-lanthanide oxide catalyst has shown 
that CeO2 was more active than the other lanthanide oxides.69 The selective partial 
hydrogenation of acetylene to ethylene was reported on Au/CeO2 in the gas phase at 300 oC.70 
The selectivity towards acetylene was 100 %. Ni/CeO2 catalysts were reported to be effective 
for the conversion of benzene to cyclohexane at 100 oC and the reaction was reported to be 
stable for at least 20 h.71 Cerium-based platinum catalysts have been extensively studied for 
the hydrogenation of crotonaldehyde. On chlorine-free Pt/CeO2, a crotyl alcohol selectivity 
has been reported to be 83 % in the hydrogenation of crotonaldehyde.72 
 
 
20 | P a g e  
 
2.5.2 Titania 
Titania is an oxide of titanium. Its chemical formula is TiO2. It has many crystal forms. These 
forms include rutile, anatase and brookite.73 Rutile is the most stable form of titania. 
Commercial titania (Degussa, P25) typically contains 85 % anatase and 15 % rutile. 
 
Titanium dioxide is a white powder with high opacity, brilliant whiteness, excellent covering 
power and resistance to colour change. These properties have made it a valuable pigment and 
opacifier for a broad range of applications in paints, plastic goods, inks and paper.74 Titania 
shows photochemical properties, such as high refractive index, excellent transparency in the 
visible and near infra red region, as well as high performance in the photocatalysis of water 
splitting and for degradation of organic compounds under UV light irradiation.75 Also, TiO2 
is a widely used oxide semiconductor material used in dye-sensitized solar cells. 
 
Palladium nanoparticles supported on titania have been used in the hydrogenation of 
acetylene.76 These catalysts showed 66.8 % selectivity for ethylene after 10 h. In the 
hydrogenation of heptyne, Pd/TiO2 showed a very high selectivity of at least 90 % to 
heptene.77. The hydrogenation of propylene has been studied on Pt/TiO2, Pt?Au/TiO2 and 
Pt2Au4/TiO2 catalysts.78 It is also important to note that TiO2 has been implicated in strong 
metal support interactions.79 
2.6 Combination of ceria and carbon materials 
Several studies have been done on the enhancement of the catalytic activities when ceria has  
been added to metals supported on carbon materials. Most studies have focused on fuel cells. 
Wang et al80, reported a comparison between Pt-CeO2/CNTs and Pt supported on CNT in 
terms of their electrochemical active surface (EAS) areas, methanol electro-oxidation activity 
and chronoamperometry. The results indicated that CeO2 can enhance the catalytic activity of 
Pt for methanol electro-oxidation with no apparent decrease of EAS. Similar results were also 
obtained by Xu and Shen81 for the electrochemical oxidation of ethanol. It was shown that Pt-
 CeO2/C gave a better performance than Pt/C. Compared with Pt/CNT, Pt?CeO2/CNT 
exhibited higher catalytic activity for methanol electro-oxidation.82 
 
In the hydrogenation of citral, Pt?CeO2/C has been reported to have a good activity.83 The 
conversion of citral reached close to 100 %, when the catalyst was reduced at 200 oC. The 
21 | P a g e  
 
main products reported were citronellal, unsaturated alcohols (geraniol and nerol) and the 
saturated alcohol, citronellol. For hydrogenation reactions, not much has been done to 
examine the effect of adding ceria to a carbon material supported catalyst. 
2.7 Preparation methods for supported catalysts 
The purpose of this sub-section is to present a general overview of the most common 
synthetic methods used for fabricating supported catalysts. The methods include low 
temperature chemical precipitation, deposition precipitation, colloidal, sol-gel, impregnation, 
microemulsions, electrochemical methods and the microwave heated polyol method. It is 
important to note that there is no single method which is superior to any other. Methods 
depend on the end applications of the catalyst and chemicals available.84 
2.7.1 Low temperature chemical precipitation 
Platinum based catalysts can be made by chemical precipitation at low temperature. 
Supported and unsupported catalyst can be made and the process involves the addition of a 
reducing agent to a platinum salt solution. Bi-metallic catalysts can be made by co-
 precipitation of a solution of two metal precursor salts. The precursor salt is reduced to the 
metallic state and will precipitate out of solution. For supported catalysts, the support is 
added prior to metal precursor reduction. A typical example is the reduction of 
hexachloroplatinic acid using sodium borohydride.85 The advantage of this method is that the 
preparation occurs under mild conditions i.e. at low temperatures. 
2.7.2 Deposition precipitation 
Deposition of a precursor of an active component from a solution onto a support can be 
brought about by chemical reactions. This is done by adding an excess solution of the 
precursor with respect to the pore volume of the support and using the support in the form of 
a powder. Deposition precipitation can be realized in a number of ways: 
? Increase in solution pH 
? Change of valency of the metal ion 
? Removal of a stabilizing ligand surrounding the metal ion 
A typical example is the synthesis of nickel nanoparticles supported on CNFs. The increase 
in pH brought about by hydrolysis of urea has led to the deposition of nickel from aqueous 
solution.  
22 | P a g e  
 
The following reactions are envisaged: 
CO(NH2)2 (aq) + 3H2O ? CO2 (g) +2NH4+ (aq) + 2OH- (aq) 
Ni2+ (aq) + 2OH- (aq) ? Ni(OH)2 (s) 
The nickel hydroxide deposited on the CNF was reduced at elevated temperatures. Ni 
particles with sizes ranging from 6-8 nm were reported to be obtained by this method.86 The 
advantage of the deposition precipitation technique is: its reproducibility, high metal loadings 
can be achieved, high metal dispersion at high metal loading and a uniform distribution of the 
active component over the support. 
2.7.3 Colloidal methods 
The method is similar to the chemical precipitation method. However it involves the addition 
of a capping agent or protecting agent. A capping agent is a material that prevents 
agglomeration of the catalyst particles and can be used to control particle size. Common 
capping agents include ligands, surfactants or polymers. The experimental procedure entails 
combining the metal source, a reducing agent, support, and a capping agent and mixing the 
reagents together under appropriate reaction conditions. The colloidal metal particles 
obtained are stabilized by either steric hindrance or by electrostatic charges. A typical 
example is the synthesis of Pt/C using the surfactant SB12.87 
The advantage of using the colloidal method is that a narrow size distribution of metal 
nanoparticles is obtained. The major drawback is the presence of the protecting agent, which 
may hinder the catalytic performance of the nanoparticles. The protecting agent can be 
removed by decomposition at elevated temperatures. Due to a sintering effect the distribution 
of metal particles are affected by template removal, and can result in lowered catalytic 
performance.88 
2.7.4 Sol-Gel method 
The sol-gel technique begins with the formation of suspended particles (a sol) that is aged 
and dried to form a semi-solid suspension of particles in a liquid (a gel), which is finally 
calcined resulting in formation of a mesoporous solid or powder. There are four distinct steps 
involved in the sol-gel technique: 89 
1. Formation of the gel 
2. Aging to allow fine tuning of the gel 
23 | P a g e  
 
3. Drying to remove the solvent from the gel 
4. Calcination to permanently change the physical and chemical properties of the solid 
Hu et al90 reported the synthesis of Pt/Al2O3 using the sol-gel technique. The advantage of the 
sol-gel technique is that it allows the control of size through the aging and calcination steps. 
This method can be used to produce catalysts with a uniform metal distribution, tuneable 
particle size, high surface area, and stable dispersion.90 The major drawback associated with 
this method is that the catalytic nanoparticles may be buried within the structure rather than 
within the pores. If the particles are not located near the pores they will not be accessible to 
reactants and therefore will not generate efficient catalysts. 
2.7.5 Impregnation 
Impregnation is the most commonly used method to fabricate catalysts. The method involves 
the impregnation of the support material with the salt solution containing the metal to be 
deposited. This is followed by a reduction step. The reduction step can either be carried out 
by liquid phase reduction using borohydride, formic acid and hydrazine as a reducing agent, 
or gas phase reduction using hydrogen as a reducing agent under elevated temperatures. For 
example, Zhou et al91 synthesized Pt nanoparticles supported on XC-72R carbon black using 
formaldehyde as a reducing agent. 
The advantage of the impregnation method is that it is simple and can be used for mass 
production of supported catalysts. However its drawback is that the metal particles have a 
large size, a broad size distribution of the catalyst particles and a poor reproducibility.91 
2.7.6 Microemulsions  
Microemulsions are also known as reverse micelles. At high water concentration an emulsion 
consists of small oil droplets surrounded by a continuous water phase. At a high oil 
concentration an emulsion consists of small water droplets surrounded by a continuous oil 
phase. Since most metal precursors are inorganic salts they are soluble in water, hence 
emulsions made of high oil concentrations are used. Reverse micelles are water-in-oil 
droplets stabilized by a surfactant. A very commonly used surfactant is sodium bis(2-
 ethylhexyl)sulfosuccinate (Na(AOT)). The droplets are dispersed randomly in solution and 
are subject to Brownian motion. They exchange water content and re-form into distinct 
micelles. The size of the water-in-oil droplets increases with increasing water content. The 
24 | P a g e  
 
droplet size and the resulting particle size can be influenced by the chain length of the 
stabilizer. 
In order to obtain the catalyst nanoparticles, the metal salt is reduced by adding a reducing 
agent into the microemulsion system. When the nanoparticles are formed, they are deposited 
onto the support, which is done by adding a solvent such as tetrahydrofuran (THF) in 
conjunction with the support powder to the microemulsion system. For example, Pt-Ru 
catalysts can be formed using the microemulsion techniques and have been directly deposited 
onto carbon black without the need of an emulsion-breaking solvent (such as THF).92 The 
advantage of the  microemulsion method is the ability to control particle size easily by 
varying the synthesis conditions. Unfortunately, the catalyst fabrication by microemulsions is 
costly since expensive surfactants and oils are needed. Furthermore, both surfactants and the 
oils can have a negative environmental impact. 
2.7.7 Electrochemical deposition 
Electrochemical deposition occurs at the interface of an electronically conductive substrate 
and an electrolyte solution containing the salt of the metal to be deposited. There are five 
stages to the electrochemical deposition of metals: 
1. Transport of metal ions in solution to the electrode surface 
2. Electron transfer 
3. Formation of metal ad-atoms via adsorption 
4. Nucleation and growth of metal particles 
5. Growth of the three-dimensional bulk metal phase 
If growth is stopped at the fourth step it results in the production of nanoparticles and if 
growth is continued metal films will be produced. Deposition occurs when the substrate has 
been supplied with sufficient potential to reduce the metal salt to a zero valent state: 
Mz+ + ze- ? M0  
The electrochemical method has been used to deposit Pt onto carbon substrates at the anode 
and cathode of fuel cells to improve the Pt utilization and reduce the Pt loading.93 The 
advantage of using the electrochemical method is that nanoparticle size can be controlled by 
controlling the deposition potential and time. 
 
 
25 | P a g e  
 
2.7.8 Polyol method 
Microwave irradiation through dielectric heating loss is a fast, simple and uniform energy 
efficient method that has been used to synthesize metal catalysts. The microwave heating 
process has been used in place of a conventional heating method to produce supported 
catalysts.94 For example, in the conventional method, a polyol (most commonly ethylene 
glycol) solution containing the metal salt is refluxed at 160 oC for 3 h to decompose the 
polyol to yield an in situ generated reducing species for the reduction of the metal ions to 
their elemental state.88 The fine metal produced can be captured by the support material 
suspended in the solution. For the microwave method, a polyol solution containing the metal 
salt is put into a microwave oven and heated.94 A typical synthesis can be outlined as 
follows:94 an aqueous solution of H2PtCl6 is mixed with ethylene glycol and the pH of the 
solution adjusted by the addition of KOH. Then, the purified CNTs are uniformly dispersed 
in the mixed solution by ultrasound. After a period of microwave heating, the resulting CNTs 
are filtered and the residue washed with acetone. The residue is then dried at 100 oC 
overnight in a vacuum oven. 
The pH value of the Pt precursor solution is an important factor for the preparation of Pt/CNT 
catalysts by the polyol process. Li et al95 found out that at a lower pH range (pH 3.6-5.8), the 
Pt nanoparticles are agglomerated and not well dispersed on the CNT surface. On the other 
hand a more uniform dispersion of Pt nanoparticles were formed in the pH range 7.4-9.2. The 
proposed mechanism to explain the pH effect during the formation of the Pt nanoparticles in 
ethylene glycol solution is:  
CH2OHCH2OH (l)? CH3CHO (l) + H2O (l) 
2CH3CHO (l) + (PtCl6)2- (aq) + 6OH- (aq) ? 2CH3COO- (aq) + Pt (s) + 6Cl- (aq) + 4H2O (l) 
 
The acetate formed can act as a stabilizer by forming a chelate-type complex via the acetyl 
groups. The polyol method is very attractive as it is a simple and straightforward method to 
synthesize catalysts. 
2.8 Hydrogenation of ethylene 
The hydrogenation of ethylene involves the addition of molecular hydrogen to ethylene to 
yield ethane. The reaction is exothermic such that temperature control is essential.  
 
26 | P a g e  
 
The equation for the formation of ethane is shown below: 
C2H4 (g) + H2 (g) ? C2H6 (g) 
The reaction occurs in the presence of a catalyst. Most of the catalysts used contain transition 
metals or transition metal oxides. The hydrogenation catalysts frequently used are grouped 
into two types; base metals (Ni, Cu and Co) and platinum group metals (Pt, Pd, Rh, Ru and 
Ir). The advantage of the base metals is that they are cheap compared to the platinum group 
metals. However they require high temperature and pressure in their operation. The platinum 
group metals on the other hand can be used under milder conditions and small amounts of 
catalyst are used.  
2.8.1 Why hydrogenate ethylene? 
Ethylene hydrogenation has been selected to evaluate the catalytic properties of various 
catalysts because the reaction is structure insensitive96 and occurs at low temperature, 
yielding only one product ethane.97 Structure insensitivity implies that the activity of ethylene 
hydrogenation is independent of the catalyst particle morphology. In other words the particle 
size of the catalyst does not affect the activity of the reaction. Somorjai98 described structure 
insensitivity as a reaction in which the kinetics (rate, activation energy) are the same for a 
crystal surface, dispersed particles, films and metal foils. The difference in rate will be 
associated with different supports. The other advantage of using ethylene is that it has a high 
reaction rate when forming ethane. 
2.8.2 Studies undertaken using ethylene hydrogenation 
Hydrogenation of ethylene has been used as a probe reaction in many studies. The 
hydrogenation of ethylene has received much attention and a full understanding of its 
chemistry provides information about hydrogenation, exchange, dehydrogenation and 
isomerization of more complicated alkenes.99 For example, the principle involved in a 
hydrogenation reaction has been used to understand the catalytic hydrogenation of 
unsaturated vegetable oils used in the production of margarine.100  
Park and co-workers101 used the hydrogenation of ethylene to investigate the catalytic 
behaviour induced by supporting nickel on three different types of graphite nanofibers. In the 
process they managed to evaluate the potential of graphite nanofibers as a support medium 
and also the impact of the orientation of the graphite platelets on the catalytic activity and 
selectivity of the metal.  
27 | P a g e  
 
Ethylene hydrogenation has been studied as a probe reaction by Gao et al102 using MoAl 
alloy films to allow the straightforward comparison between the chemistry on the alloy, the 
carbide and oxycarbide phases. They reported that molybdenum oxycarbide materials were 
inactive for the hydrogenation of ethylene because of site blockage by oxygen on the surface 
of the catalyst.  
Grunes et al, 103 described the hydrogenation of ethylene as structure insensitive and used it to 
determine in situ the active metal surface area of a platinum nanoparticle array model 
catalyst. It has been reported that ethylidyne, di-? bonded ethylene, and ?-bonded ethylene 
were present during the ethylene hydrogenation reaction.104 Of interest was the fact that 
ethylene hydrogenation occurs at the same rate regardless of whether ethylidyne is present or 
absent. 
Several other studies have been conducted using the hydrogenation of ethylene which include 
reports on the activity of oxides (e.g. zinc oxide105), determining optimum conditions106 and 
the effect of particle size107 using Ni catalysts, kinetic studies (for example using a Pt (111) 
surface108), and the activity of supported Pt catalysts109. 
2.9 Mechanism of ethylene hydrogenation 
There are three main mechanisms that have been used to describe the hydrogenation of 
ethylene. These include the Horiuti-Polanyi mechanism, the Twigg mechanism and the 
Jenkins-Rideal mechanism. 
2.9.1 Horiuti-Polanyi mechanism 
The Horiuti-Polanyi mechanism110 states that the adsorption of ethylene occurs on the surface 
of a transition metal (for example Pt) by using one of the carbon-carbon double bonds. This is 
followed by hydrogenation with atomic hydrogen (formed from the dissociatively adsorbed 
molecular hydrogen) through an ethyl intermediate to ethane. The ethane is finally desorbed 
into the gas phase. The illustration of the Horiuti-Polanyi mechanism is shown in Figure 2.6. 
 
 
 
 
 
28 | P a g e  
 
 
 
Figure 2.6. Horiuti-Polanyi mechanism for hydrogenation of ethylene. (1) Diffusion of ethylene and 
hydrogen to the metal surface. (2) Ethylene and hydrogen adsorption on the metal surface. Hydrogen 
dissociates on the surface to form hydrogen atoms. (3) One of the surface hydrogen atoms reacts with 
adsorbed ethylene to form surface ethyl. (4) The other hydrogen atom reacts with the ethyl radical 
bound on the surface to form ethane. Ethane desorbs from the catalyst surface.99 
2.9.2  Twigg mechanism 
The Twigg mechanism111 suggests that the hydrogen molecules are first dissociated into 
atoms on the catalytic surface through reaction with ethylene and hydrogenation takes place 
after the addition of another hydrogen atom. The Twigg mechanism is shown in Figure 2.7.  
29 | P a g e  
 
 
Figure 2.7. Twigg mechanism of ethylene hydrogenation. (1) Diffusion of ethylene to the catalyst 
surface. (2) Ethylene is adsorbed on the catalyst surface. (3) Adsorbed ethylene reacts with hydrogen 
to give an ethyl group and adsorbed hydrogen atom. (4) The ethyl radical bound on the catalyst 
surface react with adsorbed hydrogen atom to form ethane which desorbs from the Ni surface.111 
2.9.3 Jenkins-Rideal mechanism 
The Jenkins-Rideal mechanism112 proposes that the gas phase ethylene reacts with adsorbed 
hydrogen to produce ethane. The first step in the mechanism involves hydrogen being 
chemisorbed on to the surface of the catalyst. The second step is the reaction between bulk 
ethylene with adsorbed hydrogen to produce ethane. The third step entails the flow of ethane 
out of the reaction zone. 
2.10 Hydrogen adsorption and surface migration 
During hydrogenation reactions, molecular hydrogen diffuses to the catalyst surface where it 
is adsorbed. After adsorption on the metal surface, it dissociates to form hydrogen atoms. The 
hydrogen atoms can migrate into the metal crystallite and in some cases react with the metal 
to form metal hydrides. The metal surface in which hydrogen has penetrated may be less 
reactive, since rearrangement of the surface is required to release the hydrogen atoms. The 
difficulties that may arise in releasing a hydrogen atom during a reaction are shown in Figure 
2.8. 
 
Figure 2.8. Possible extremes in hydrogen adsorption. (i) Hydrogen is adsorbed without a chemical 
reaction. (ii) Hydrogen reacts with
 For the hydrogenation activity, Fi
 available for reaction. Surface migration of atomic hydrogen is a phenomenon of great 
interest, for it appears to have a si
 process has been called spillover when it involves surface diffusion from the metallic site to 
the support (C, Al2O3, SiO2). Hydrogen spillover has been observed in Pt/ZrO
 Pt/TiO2 systems.  
In hydrogenation, the supported metal may adsorb and activate hydrogen whilst the support 
may adsorb the substance to be hydrogenated and the reaction may proceed on the support 
surface as a result of hydrogen spillover. For example the increase
 hydrogenation on Pt/SiO2 catalyst diluted with SiO
 spillover.113  
It has been shown that the hydrogenation of pent
 Pt/SiO2 was very fast at 100  
effected by the hydrogen adsorbed on Pt and 
adsorbed on SiO2. 
 the metal surface to form a hydride.1 
gure 2.8 (i) is preferred as the atoms of hydrogen would be 
gnificant effect on catalysis in some reactions.
  in the rate of ethylene 
2 or Al2O3 has been attributed to hydrogen 
-1-ene to pentane by hydrogen adsorbed on 
oC.113 It has been suggested that at first the hydrogenation is 
later it is effected by the spillover hydrogen 
30 | P a g e  
 
113
  The 
2, Pt/SiO2 and 
 
Beside an increase in the rate of activity, hydrogen spillover offers other advantages
 include: 
? The hydrogen participating in the spillover can also interact with organic deposits and 
can ensure the removal of coke
 ? Hydrogen spillover can also promote an increase in the rate of adsorption of hydrogen
 Figure 2.9. Removal of carbonaceous deposit by reaction of spillover hydrogen, leading to restoration 
of catalytic site. 
2.11 Summary 
From the literature cited in the preceding sections, it is clear that they are many factors which 
affect hydrogenation reactions
 in turn will result in different catalytic activities. The hydrogenation of ethylene has been 
used as a probe reaction because of its simplicity and also to determine the possible 
mechanism of the hydrogenation reaction of more complicated alkenes. It is also important to 
note that during hydrogenation, hydrogen adsorption and surface migration can also occur 
and may have a negative effect if the hydrogen reacts with the metal surface.
  
 
 
 
 
 
 
 
114
  as shown in Figure 2.9. 
. The different supports possess different morphologies which 
31 | P a g e  
 which 
 
 
 
32 | P a g e  
 
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37 | P a g e  
 
CHAPTER THREE 
EXPERIMENTAL  
 
3.1 Introduction 
This chapter presents the detailed synthesis of carbon materials used in the study and the 
procedure used to deposit platinum onto the carbon materials, ceria and titania. The 
characterization techniques used in this project are also discussed. Finally, a discussion of the 
hydrogenation reactions performed using different platinum supported catalysts is given. 
3.2 Materials and chemicals  
All the chemicals used in this project were reagent grade. Solvents were obtained in high 
purity from the suppliers unless otherwise mentioned. The carbon materials (carbon 
nanotubes (CNTs), coiled carbon nanofibers (CCNFs) and carbon spheres (CS)) were 
synthesized in the laboratory using the chemical vapour deposition (CVD) method. Activated 
carbon and titania (Sigma Aldrich) were used without further purification. Ceria was 
synthesized in the laboratory using the sol-gel technique. 
3.3 Synthesis of carbon materials 
There are three major synthetic methods that are used to synthesis carbon materials. These 
methods include laser ablation, arc discharge and chemical vapour deposition (CVD). CVD 
has been selected for use in this study because it generates materials with a high purity and 
can be scaled up for mass production. The carbon materials were synthesized using the CVD 
method. A schematic experimental setup for CVD growth is shown in Figure 3.1. The growth 
process involves heating a catalyst material to high temperature in the tube furnace followed 
by passing hydrocarbon gas through the tube reactor for a period of time. The carbon 
materials grown over the catalyst were collected upon cooling the system to room 
temperature. Some key parameters in carbon material growth are the hydrocarbon, as well as 
the catalyst and temperature. 
 
Figure 3.1. A schematic CVD setup for carbon material synthesis.
 3.3.1 Catalyst preparation for CNTs
 The synthesis of carbon nanotubes was performed using 
deposition technique. The catalyst used for the 
the preparation of a 5 % Fe
 (Fe(NO3)3.9H2O and Co(NO3
 precursor solution. The solution was then added dropwise to 10 g of support (C
 stirred for at least an hour at room temperature. The mixture was then filtered and the slurry 
was allowed to semi-dry at room temperature for 30 minutes. The catalyst was then placed in 
an oven at 120 oC for 12 h and calcined at 400 
3.3.2 Synthesis of CNTs1 
The carbon nanotubes were obtained by the catalytic decomposition of acetylene over the 
supported Fe-Co/CaCO3 catalyst. The furnace was electronically controlled such that the 
heating rate, reaction time, reaction temperatu
 as desired. In a typical synthesis protocol, 1 g of Fe
 on a small quartz boat that was
 heated at 10 oC/min under the flow N
 temperature of 700 oC, the flow of N
 introduced at a flow rate of 90 m
 and the reactor was cooled under N
 1
  
the catalytic chemical vapour 
synthesis was Fe/Co supported on
 -Co supported catalyst, the selected Fe and Co precursors 
)2.6H2O) were dissolved in water (25 mL) to make a 50:50 
oC for 16 h in air. 
re and gas flow rate were accurately maintained 
-Co/CaCO3 catalyst was uniformly s
  placed at the centre of a horizontal furnace. The furnace was 
2 (40 mL/min) to 700 oC. After reaching the desired 
2 was increased to 240 mL/min and acetylene was 
L/min for 1 h. Thereafter the flow of acetylene was stopped 
2 at 40 mL/min to ambient temperatures. The small quartz 
38 | P a g e  
 
 
 CaCO3. For 
aCO3) and 
pread 
39 | P a g e  
 
boat was then removed from the reactor and the product was collected along with the  
catalyst. 
3.3.3 Catalyst preparation for CCNFs2 
The catalytic system used for CCNF synthesis involved copper supported on TiO2. For the 
preparation of 5% copper supported catalysts, the selected copper precursor (Cu(NO3)2?3H2O, 
Sigma-Aldrich) was dissolved in distilled water to form a homogeneous solution (0.262 M). 
The solution was then added dropwise (5 mL/min) to the support powder (TiO2, Degussa 
P25, Sigma-Aldrich) under stirring to form a suspension. After 90 minutes of stirring the 
suspension was heated to 60 ?C and isothermal evaporation under stirring was then carried 
out. The resulting product (Cu/TiO2) was finally ground and sieved using a 500 ?m mesh 
sieve. The catalyst was then placed in an oven at 100 ?C for 12 h and calcined at 400 ?C for 
16 h in air. 
3.3.4 Synthesis of CCNFs2 
The coiled carbon nanofibers were obtained by the catalytic decomposition of acetylene over 
the supported copper catalyst following the same path as of CNTs synthesis. The furnace was 
electronically controlled such that the heating rate, reaction temperature and gas flow rate 
were accurately maintained as desired. In a typical run, approximately 0.8 g of catalyst 
material was uniformly spread onto a small quartz boat, and placed in the centre of a 
horizontal furnace. The catalyst was then activated by heating at 10 ?C/min in H2 at 
100 mL/min to a temperature of 250 ?C. At 250 ?C acetylene at a flow rate of 100 mL/min 
was introduced for 1 h. Thereafter the flow of acetylene was stopped and the reactor was 
cooled under H2 to ambient temperature. The resultant material was then harvested for 
characterization and stored for later use.  
 
3.3.5 Purification of CCNFs 
The CCNFs produced were mixed with the residual titania from the catalyst (Cu/TiO2). 
Hydrofluoric acid (HF) was used to remove the titania. In a typical purification process, 100 
mL of 40% HF (the operation was carried in a fume hood) was placed into a 250 mL plastic 
beaker and 0.5 g of CCNFs was added. The mixture was sonicated for 5 minutes. Thereafter 
the mixture was left in the fume hood for 12 h. The mixture was then separated using a filter 
paper and washed with distilled water until the pH of the filtrate was around 7. The HF 
treated CCNFs were then dried in an oven at 120 oC for 12 h. 
40 | P a g e  
 
3.3.6 Synthesis of carbon spheres3 
The carbon spheres were obtained by decomposition of acetylene at high temperatures. The 
furnace (vertical) was electronically controlled such that the heating rate, reaction 
temperature and gas flow rate were accurately maintained as desired. The furnace was heated 
at 10 ?C/min in Ar at 100 mL/min to a temperature of 900 oC. At 900 oC acetylene was 
introduced for 1 h. Thereafter the flow of acetylene was stopped and the reactor was cooled 
under Ar at 100 mL/min to ambient temperature. The product was then harvested for 
characterization and stored for later use. 
3.3.7 Summary of the carbon materials synthesis procedures 
Table 3.1 shows the reaction conditions used for the synthesis of the different carbon 
materials. 
Table 3.1: Summary of the carbon materials synthesis conditions 
Carbon Materials CNTs CCNFs CSs 
Temperature 700 oC 250 oC 900 oC 
Catalyst Co-Fe/CaCO3 Cu/TiO2 No catalyst 
Carbon source Acetylene Acetylene Acetylene 
3.4 Functionalization of carbon materials 
The chemical structure of CMs consists mainly of carbon atoms and as such, they do not 
contain any functional groups. Chemical functionalization therefore plays an essential role in 
tailoring the properties and application versatility of CMs.4 Most of the functional groups are 
formed by oxidation of the carbon materials. Oxidation can be carried out in the gas phase 
using oxygen, ozone and carbon dioxide, or in the liquid phase using strong acids such as 
nitric acid, sulphuric acid or other oxidizing agents, such as NaOCl, H2O2, KMnO4, K2Cr2O7 
and OsO4.5 In this project functionalization was performed using nitric acid. 
3.4.1 Oxidation of carbon materials 
Prior to oxidation of the carbon materials, polyaromatic compounds were extracted for 12 h 
using 100 mL of toluene in a Soxhlet apparatus. During the Soxhlet extraction, the 
41 | P a g e  
 
hydrophobic graphite particles were dispersed and removed from the carbon materials. The 
thimble containing the residual carbon materials was collected and vacuum-dried at 333 K for 
12 h.6 The purified carbon materials were oxidized with concentrated nitric acid at 
temperatures of 50 oC (for 12 h) and 100 oC (for 3 h). In a typical oxidation process, 1 g of 
CNTs was placed in a 250 mL round bottom flask containing 100 mL of concentrated nitric 
acid. The mixture was sonicated for 15 minutes in a ultrasonic bath at room temperature. The 
mixture was then stirred for 12 h at a temperature of 50 oC. Thereafter the mixture was 
diluted with distilled water and filtered using a B?chner funnel and filter paper (MN 615, 110 
mm). The CNTs were then washed several times with water until the filtrate had a pH of 
approximately seven. Finally the CNTs were dried in an oven at 120 oC for 12 h. 
 
The amount of functional groups (hydroxyl, carboxyl, carbonyl, etc) attached to the walls of 
the CMs were estimated by using an alkalimetry titration method. In this method, the 
oxidized CMs were suspended in a NaCl (0.1 mol dm-3) electrolyte. Ion exchange occurs 
between the cations of the electrolyte and the active hydrogen of the functional groups 
leading to hydrogen ions being evolved. The change of the pH of the suspension during the 
addition of the titrant is due to the progressive dissociation of acidic groups. The quantities of 
strong acids detected correspond to the acid group dissociated in solution of pH less than 7. 
Stronger acids with pKa less than 7 mainly comprise of carboxylic acids and these can be 
titrated using a very weak base such as NaHCO3.  
3.5 Synthesis of ceria7 
Ceria was prepared by a sol-gel method. Cerium nitrate solution with a concentration of 0.1 
M was mixed with a 0.4 M urea solution. The mixture was aged at 100 oC for 50 hours. The 
precipitate that formed was washed with water and ethanol. Ceria was then dried overnight at 
100 oC and then calcined at 300 oC for 2 h.  
3.6 Synthesis of the supported platinum catalyst 
Platinum was deposited on the various supports (carbon materials, ceria and titania) using the 
polyol method. 
3.6.1 Synthesis of platinum supported on carbon materials (Pt/CM)8 
The synthesis was done using the microwave assisted polyol synthesis. Before the Pt/CM was 
synthesized, UV-vis spectroscopy was used to follow the formation of Pt from 
42 | P a g e  
 
hexachloroplatinic acid. The method used ethylene glycol as both a solvent and reducing 
agent. The method was chosen because it is a straightforward, inexpensive catalytic synthesis 
method of low toxicity. In the method, the CCNFs (0.2 g) were dispersed in 50 mL of 
ethylene glycol solution. The CCNFs in solution were sonicated for 15 minutes until all 
agglomerates were broken down and dispersed evenly. The solution was mechanically stirred 
for 30 minutes and 0.21 mL of 0.05 M H2PtCl6 was added dropwise and the solution was 
further stirred for 3 hours to ensure that the precursor ions would be distributed evenly 
throughout the solution and dispersed evenly on the support. The mixture was then irradiated 
in a microwave oven (input power 810 W) for 4 minutes with on?off cycle (60 s on ? 120 s 
off). For comparison, the mixture was refluxed for 3 h using an oil bath at a temperature of 
160 oC. The product was filtered and washed with acetone and distilled water. The residue 
(Pt/C) was then dried at 120 oC for 12 h. 
3.6.2 Synthesis of platinum supported on oxides 
The Pt/CeO2 and Pt/TiO2 were prepared by reduction of H2PtCl6 on CeO2 and TiO2 supports. 
The method is similar to the synthesis used to produce Pt/CM catalysts. Ceria and titania 
were used instead of the carbon nanomaterial.  
3.6.3 Synthesis of Pt-CeO2/CM9 
The Pt-CeO2/CM was prepared using the polyol process. The appropriate amount of cerium 
nitrate, H2PtCl6, and sodium acetate were added into a solution of ethylene glycol. The 
mixture was uniformly mixed with a carbon nanomaterial by sonication. The resultant 
mixture was irradiated in the microwave oven (input power 810 W) for 4 minutes with on?off 
cycle (60 s on ? 120 s off). Afterwards the suspension was filtered and the residue was 
washed with acetone and deionized water. The solid products were dried at 120 oC for 12 h in 
an oven.  
The Pt-CeO2/CM catalysts were also synthesized by making CeO2/CM first and then 
depositing platinum on the support (CeO2/CM). The CeO2/CM was synthesized by the polyol 
method. Cerium nitrate and sodium acetate were added to a beaker containing 50 mL of 
ethylene glycol. The mixture was then mixed for 30 minutes and CM was added into the 
mixture. Stirring was done for 3 h. The resultant mixture was irradiated in the microwave 
oven (input power 810 W) for 4 minutes with on?off cycle (60 s on ? 120 s off). Afterwards 
43 | P a g e  
 
the suspension was filtered and the residue was washed with acetone and deionized water. 
The solid products were dried at 120 oC for 12 h in an oven.  
The solid product (0.2 g) was dispersed in 50 mL of ethylene glycol solution. CeO2/CM in 
ethylene glycol solution was sonicated for 15 minutes until all agglomerates were broken 
down and dispersed evenly. The solution was mechanically stirred for 30 minutes and 0.21 
ml of 0.05M H2PtCl6 was added dropwise and the solution was further stirred for 3 hours to 
ensure that the precursor ions would be scattered throughout the solution and dispersed 
evenly. The mixture was then irradiated using a microwave oven (input power 810 W) for 4 
minutes with on?off cycle (60 s on ? 120 s off). The product was filtered and washed with 
acetone and distilled water. The residue (Pt-CeO2/CM) was then dried at 120 oC for 12 h. 
3.7 Characterization techniques used in this study 
The following techniques were used to characterise the supports and the catalysts: 
transmission electron microscopy (TEM) equipped with energy dispersion X-ray (EDX) 
capabilities, thermal gravimetric analysis (TGA), ultraviolet-visible spectrophotometry (UV-
 Vis), Raman spectroscopy, temperature programmed reduction (TPR), X-ray diffraction 
(XRD), Brunauer-Emmett-Teller N2 adsorption (BET), Fourier transform infrared (FTIR) 
spectroscopy and inductively coupled plasma atomic spectra emission spectroscopy (ICP-
 AES) 
3.7.1 Transmission electron microscopy 
Transmission electron microscopy (TEM) is a technique that is used to confirm the 
morphology of the materials. The beam of light is able to pass through the sample and the 
transmitted electrons produce an image of the sample. TEM is a useful tool and is used 
extensively for the characterization of organic and inorganic materials. In this study, the TEM 
analysis (FEI Tecnai G2 Spirit electron microscope at 120 kV) was used to determine the 
aggregate morphology, particle size and particle size distribution of either the support or the 
catalyst. The EDX was used to obtain the composition of the catalyst. 
 A small quantity of a sample to be analyzed was placed in a glass vial containing 5 mL of 
methanol. The mixture was then sonicated for 15 minutes to give a homogeneous suspension 
of the sample in the solvent. A drop of the suspension was then spread on a carbon copper 
grid (200 mesh) and allowed to dry at room temperature. The grid was then mounted onto an 
exchange rod and placed into the TEM chamber and was ready for viewing. 
44 | P a g e  
 
3.7.2 Thermal gravimetric analysis 
Thermal gravimetric analysis (TGA) is a technique that is used to study the changes in a 
sample with variation in heating temperature. The changes are usually associated with weight 
loss resulting from dehydration or decomposition of the sample as the temperature increases. 
The weight loss can also arise from the formation of physical and chemical bonds that can 
lead to the release of volatile compounds. In this study, the material?s thermal stability was 
studied using a Perkin Elmer Thermogravimetric Analyzer (TGA 4000). 
About 0.05 g of the sample was used for the thermal gravimetric analysis. The sample was 
placed into a high temperature alumina cup that was supported on an analytical balance 
located in the furnace chamber. The balance was zeroed, and the sample was heated from 
ambient temperature to 900 oC at the rate of 10 oC per minute. The weight loss with increase 
in temperature was automatically recorded. The TGA curve plots the TGA signal, converted 
to percent weight change on the Y-axis against the temperature on the X-axis. 
3.7.3 Ultraviolet-visible spectrophotometry 
UV-vis spectrophotometry is used to determine the absorption or transmission of UV-vis 
light (180 to 820 nm) by a sample.10 It is applicable to qualitative and quantitative 
determination of many organic and inorganic compounds in a solution. Compounds analysed 
by this technique must have chromophores (covalently bonded but unsaturated groups such as 
NO2, C=C and C=O) that absorb electromagnetic radiation in the ultraviolet and visible 
region of the spectrum. The amount of energy absorbed is directly proportional to the 
concentration of the compound in the solution. 
Samples were placed in a cuvette that was 1 cm wide and 4.5 cm long. The cuvette was then 
placed in the instrument and absorbances were measured. Water was used as a reference 
sample and also to re-zero the instrument. Spectra were then plotted of absorbance against 
wavelength using a Analytikjena, Specord 50 instrument. 
3.7.4 Raman spectroscopy 
Raman spectroscopy is used in chemistry and other branches of science to study vibrational, 
rotational and other low frequency modes in a sample. After a sample has been illuminated 
with a laser beam, some monochromatic radiation is scattered. The scattered light has 
45 | P a g e  
 
different energies depending on the type of molecular vibrations present in the sample. The 
backscattering radiation allows one to determine the structure and quality of the sample.11  
A Jobin-Yvon T64000 Raman spectrometer was used to measure the vibrations in the sample. 
It was operated in a single mode with 600 lines/mm grating. A 514.5 nm line of the argon ion 
laser was used as the source of excitation. Laser light was focused on to the sample using a 
20x objective lens of an Olympus microscope. The scattered light was collected in a 
backscattering configuration and was detected using a nitrogen cooled charge coupled 
detector. 
3.7.5 Temperature programmed reduction 
Temperature-programmed reduction (TPR) is a widely used tool used for the characterization 
of metal oxides, mixed metal oxides, and metal oxides dispersed on support.12 The TPR 
method yields quantitative information of the reducibility of the oxide?s surface, as well as 
the heterogeneity of the reducible surface. TPR is a method in which a reducing gas mixture 
flows over a sample. A thermal conductivity detector (TCD) is used to measure changes in 
the thermal conductivity of the gas stream. The TCD signal is then converted to the 
concentration of active gas using a level calibration 
TPR experiments on the prepared catalysts were carried out using an ASAP 2020 
Micrometrics analyzer in a 5 % H2/Ar gas mixture. Samples were pretreated with Ar at 150 
oC for 2 h. The hydrogen consumption was recorded with a TCD cell while the sample was 
linearly heated from 50 to 800 oC at 10 oC/min. 
3.7.6 X-ray diffraction 
Powder XRD is the most widely used X-ray diffraction technique to find the crystallization 
and morphology of materials. As the name suggests, the sample is usually in a powder form, 
consisting of fine grains of single crystalline material to be studied.13 The term 'powder' 
means that crystalline domains are randomly oriented in the sample. Therefore when the 2-D 
diffraction pattern is recorded, it shows concentric rings of scattering peaks corresponding to 
the various d spacings in the crystal lattice. The positions and the intensities of the peaks are 
used for identifying the underlying structure (or phase) of the material. This phase 
identification is important because the material properties are highly dependent on its 
structure. A D8 Bruker X-ray diffractometer was used for the analysis. 
46 | P a g e  
 
3.7.7 Brunauer-Emmett-Teller N2 adsorption (Surface area analysis) 
Brunauer-Emmett-Teller N2 adsorption (BET) is a technique that is used to measure surface 
area, pore volume and pore size distributions of a sample. The BET analysis was carried out 
using an automated gas adsorption analyser (Tristar 3000 V6.05) 
Samples were degassed using a Micrometrics Flow Prep 060 Sample Degas System at 120 oC 
for 12 h prior to nitrogen adsorption. The BET surface area was calculated based on the 
adsorption data in the relative pressure range of 0.001-0.20. 
3.7.8 Fourier transform infrared spectroscopy 
Fourier transform infrared (FTIR) spectroscopy is one of the most important tools used to 
identify functional groups present in a molecule or compound. FTIR spectroscopy provides 
information about the chemical bonding or molecular structure of materials. It can be utilized 
to quantify components of an unknown mixture. It can be applied to the analysis of solids, 
liquids, and gases. 
FTIR measurements were performed using a Bruker-Tensor 27-ATR FTIR spectrometer in 
the range from 4000-400 cm-1. The FTIR spectra were recorded at room temperature when 
the infrared light was passed through the sample. 
3.7.9 Inductively coupled plasma atomic spectra emission spectroscopy 
Inductively coupled plasma atomic spectra emission spectroscopy (ICP-AES) is a very 
important tool which is used to determine the percentage loading of platinum. The samples 
for ICP-AES analysis were digested in an microwave oven for 2 h with aqua regia in order to 
collect platinum ions in solution. Then, the aliquots of solution were diluted to 50 mL using 
distilled water and analyzed using inductively coupled argon plasma emission spectrometer, 
(GENESIS ICP-AES SPECTRO Analytical Instruments) 
3.8 Hydrogenation reactions 
Hydrogenation reactions were used in this study to determine the effect of adding ceria on to 
platinum supported on carbon materials. In the process, the effect of various supports was 
also determined. 
 
47 | P a g e  
 
3.8.1 Experimental set up 
The catalytic hydrogenation reactions were performed at atmospheric pressure by passing 
continuously, a gas feed containing 5 % hydrogen in argon or a 5 % ethylene in argon stream 
over the catalyst (100 mg) packed in a fixed bed steel micro-reactor. The micro-reactor was 
fitted with a thermocouple for controlling temperature. Inside the micro-reactor, there is a frit, 
which allows a passage of the gases from the micro reactor to the gas chromatograph (GC). 
During a hydrogenation reaction, the frit is covered with quartz wool in order to keep the 
catalyst in place. The sample size (amount of catalyst used) was 0.1 g. The experimental set 
up is shown in Figure 3.2. 
 
Figure 3.2. Schematic representation of the hydrogenation reaction set up 
Gas chromatography (GC) was used to characterize the products of the hydrogenation of 
ethylene. The use of the GC is to separate volatile components of a reaction mixture prior to 
GC analysis.  The separated components were detected by the GC detectors. The most 
common detectors used for gas chromatography are the flame ionization detector (FID) and 
the thermal conductivity detector (TCD). Both are sensitive to a wide range of components 
and both work over a wide range of temperatures. TCD can be used to detect any component 
48 | P a g e  
 
other than the carrier gas as long as the thermal conductivities are different from the carrier 
gas. The TCD used a Porapak Q column. 
The conditions of the GC: the column temperature was 80 oC, injector temperature was 200 
oC and the detector temperature was 100 oC. The carrier gas was Argon with a pressure of 
100 Kpa. 
The following investigations were conducted in the project: the effect of increasing the 
temperature, flow rate of gases, metal loading and the ratio of hydrogen to ethylene. The 
conversion of ethylene to ethane was calculated as follows: 
 
 
Where (t) is the time at which the conversion was taken and (0) is the initial time. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Conversion (t) = ([C2H4 (0)]-[C2H4 (t)]) x 100 % 
[C2H4 (0)] 
49 | P a g e  
 
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9. J. Zhao, W. Chen, Y. Zheng, Mat. Chem. Phys. 111 (2009) 591-595  
10. http://www.ptli.com/testlopedia/tests/UV-VIS-SPEC.asp (accessed 23 June 2009) 
11. L. A. Lyon, C. D. Keating, A. P. Fox, B. E. Baker, L. He, S. R. Nicewarner, S. P. 
Mulvaney,  M. J. Natan, Anal. Chem. 70 (1998) 341-361 
12. www.vscht.cz/kat/download/lab_tpr_eng.doc (accessed 23 June 2009) 
13. http://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.html#x2 
(accessed 23 June 2009) 
 
 
 
 
 
 
 
50 | P a g e  
 
CHAPTER FOUR 
RESULTS AND DISCUSSION 
 
4.1 Introduction 
This chapter presents the results obtained from the various experiments performed in this 
study. This includes the characterization of the carbon materials (CMs) as well as the 
platinum supported on the CMs and oxides (CeO2 and TiO2). Finally, the results for the 
hydrogenation of ethylene using the different platinum supported catalysts are discussed. 
4.2.1 TEM analysis of the carbon materials  
The carbon materials [coiled carbon nanofibers (CCNFs), carbon spheres (CS) and carbon 
nanotubes (CNTs)] were synthesized using the chemical vapour deposition method as 
described in Chapter 3. The as-synthesized CMs were characterized by transmission electron 
microscopy (TEM) and the results are shown in Figure 4.1. It was observed that the as- 
synthesized CMs (Figure 4.1 a and c) had some impurities which were suspected to be the 
remains of the catalysts used in their synthesis. There were no impurities observed in the 
TEM image of the CSs (Figure 4.1 b) as the synthesis was done in the absence of a catalyst. 
       
a b 
51 | P a g e  
 
  
 
4.2.1.2 Purification of CCNFs 
The CMs produced in this study were investigated as catalyst supports. A catalyst works best 
in the absence of impurities. The CCNFs were believed to be contaminated by titania which 
was used as a catalyst support for the Cu/TiO2 catalyst. Hydrofluoric acid (HF) was used to 
remove the residual titania and its advantage is that it does not react with CCNFs. The 
probable reaction that takes place is as follows: 
4HF (aq) + TiO2 (s) ? TiF4 (aq) + 2H2O (l) 
Therefore the TiF4 produced in solution would be removed by filtration and the CCNF would 
remain as a residue. The HF treated CCNFs were characterized by TEM in order to verify the 
disappearance of the titania residue on the CCNFs. Figure 4.2 shows the TEM images for the 
HF treated CCNFs. It was observed from TEM images that all the TiO2 was successfully 
removed by HF. Of interest is the fact that the morphology of the CCNFs were not affected 
by the HF treatment though it cannot be observed from TEM if the properties of the CCNF 
were affected by the HF treatment. Figure 4.2 shows that the material contains both coiled 
and uncoiled fibers. The estimated ratio of coils to uncoiled fibers is 60/40. 
 
 
Figure 4.1: TEM images of the as synthesized (a) CCNFs (b) CSs (c) CNTs 
c 
52 | P a g e  
 
   
Figure 4.2. TEM images of the HF treated CCNFs (a) uncoiled fibers and (b) a coiled fiber 
4.2.1.3 The effect of functionalization on the carbon materials 
Prior to functionalization (by oxidation using nitric acid), Soxhlet extraction was performed 
on the CMs. This process was performed in order to remove all the polyaromatic compounds 
left behind in the synthesis. All the carbon materials contained polyaromatic compounds as 
the colour of toluene changed from colourless to a brown solution as the Soxhlet extraction 
preceded. The intensity of the brown solution was mostly observed after extraction of the CSs 
when compared to the other carbon materials.  
There are two major reasons as to why functionalization of carbon materials was performed. 
The first reason was to improve the hydrophilic nature of the carbon materials. The as-
 synthesized carbon material does not dissolve/disperse in water, but they are rather observed 
to be suspended above the solvent. However, after oxidation the CMs could be well dispersed 
in water. The second reason was to introduce functional groups on the CMs in order to 
improve anchoring of metals onto the carbon during catalyst synthesis. Some of the potential 
functional groups introduced on the CMs are shown in Figure 4.3.1 These include oxygenated 
groups such as the COOH, OH, OR groups etc. The degree of oxidation indicates the effect 
of the severity of the oxidation treatment on the CMs. 
 
a b 
53 | P a g e  
 
 
Figure 4.3. Different oxygen-containing surface groups on the carbon materials. a) carboxyl groups, 
b) carboxylic anhydride groups, c) lactone groups, d) phenol groups, e) carbonyl groups, f) quinone 
groups, g) xanthene or ether groups.1 
 
The masses of the CMs produced were measured before and after functionalization using two 
different conditions and are shown in Tables 4.1 a and 4.1 b. 
Table 4.1a: Yield of CMs remaining after reflux for 3 h at 100 oC in nitric acid 
Carbon materials Mass before reflux 
(g) 
Mass after reflux 
(g) 
Yield (%) 
CNTs 1.025 0.9486 92.5 
CSs 1.048 0.5670 54.1 
CCNFs 1.018 0.4352 42.8 
 
Table 4.1b: Yield of CMs remaining after reflux for 12 h at 50 oC in nitric acid 
Carbon materials Mass before reflux 
(g) 
Mass after reflux 
(g) 
Yield (%) 
CNTs 1.037 0.9979 95.8 
CSs 1.069 0.9699 90.7 
CCNFs 1.034 0.9735 94.1 
 
54 | P a g e  
 
A comparison of the yields from the two functionalization modes show that there were large  
mass losses for CSs and CCNFs when the CMs were heated under reflux for 3 h at 100 oC 
(Table 4.1 a) compared to when the CMs were functionalized at 50 oC for 12 h (Table 4.1 b). 
Under reflux at 100 oC for 3 h the yields for CSs and CCNFs were 54.1 % and 42.8 % 
respectively. This suggests that CSs and CCNFs were destroyed under these conditions. This 
was confirmed by TEM analysis. Figure 4.4 shows the effect of functionalization at 100 oC 
for 3 h on the CCNFs. 
  
Figure 4.4. TEM image of CCNFs functionalized at 100 oC for 3 h 
A prolonged or high temperature reflux induces opening of CM tips or damage to the walls of the 
carbons.2 Because of this drawback, products produced after functionalization was limited to 
50 oC for 12 h and these conditions were used in later studies. It is important to note that the 
CNTs were resistant to the harsh conditions. This confirms that the CNTs have a well defined 
aromatic structure that is less readily oxidized. The TEM images of the three CMs refluxed at 
50 oC for 12 h are shown in Figure 4.5. 
55 | P a g e  
 
   
 
Figure 4.5. TEM images of (a) CNTs (b) CCNFs (c) CSs functionalized by reflux at 50 oC for 12 h.  
A marked difference between the as-synthesized CNTs (Figure 4.1) and the functionalized 
CMs (Figure 4.5) can be seen. Impurities associated with the CNTs were removed by nitric 
acid in the functionalization process. The remains of the catalyst (Fe-Co/CaCO3) used in the 
synthesis of the CNTs were removed from the external CNT surface. Changes on the CCNFs 
and CSs surfaces could not be seen by TEM. 
 The amount of acid groups attached to the CMs was estimated using alkalimetry and the 
results are shown in Table 4.2. The results show small but measurable differences for the 3 
samples. 
 
 
a b 
c 
56 | P a g e  
 
Table 4.2: Estimates of the acid groups on the carbon materials (50 oC/12 h) 
Carbon materials Acid groups (mequi/g) 
CNTs 9.2 x 10-2 
CCNFs 8.9 x 10-2 
CSs 8.3 x 10-2  
CNTsa  3.4 x 10-1 
a-acid treated at 100 oC/3 h 
From the alkalimetry results it is clear that functional groups were attached to all three of the 
CMs. CNTs functionalized at 100 oC for 3 h had more acid groups (3.4 x 10-1) than CNTs 
functionalized at 50 oC for 12 h (9.2 x 10-2). This means that the harsher the oxidation 
treatment, the more acid groups that can be attached. 
4.2.1.4 Thermal gravimetric analysis of the carbon materials 
Thermal gravimetric analysis (TGA) can be used quantitatively to evaluate the purity of the 
carbon materials, in particular the content of the residual metal and the degree of 
functionalization. The residual metal content in the carbon materials can be obtained by 
oxidizing the carbon materials in air. The carbon materials are converted to CO/CO2 in air 
and the metal or metal oxide remains at the end of the process.3 To confirm that TiO2 was 
removed from the CCNFs, TGA analysis was performed.  
Figure 4.6a show the TGA plot of the CCNFs before and after purification with HF. It can be 
clearly seen from the TGA plots that TiO2 was completely removed from the carbon. The 
residual mass before purification was 23.62 % and after purification it went down to ca. 0 %. 
It was also observed that the TGA profile of the purified CCNF showed changes at around 
200 oC. The mass loss between 200-300 oC is due to the presence of the acid groups. It can 
also be noted that both curves show a change in rate at about 400 oC suggesting two types of 
carbon are formed with CCNFs i.e. this could be related to the presence of the linear and 
coiled fibers. 
57 | P a g e  
 
0 200 400 600 800 1000
 -10
 0
 10
 20
 30
 40
 50
 60
 70
 80
 90
 100
 110
 W
 ei
 gh
 t (
 %
 )
 Temperature (?C)
 TGA
 after purification
 before purification
  
Figure 4.6a. TGA profile of CCNFs before and after purification 
Functionalization of the CNTs had a dual purpose. The first was to remove the residual metal 
after synthesis from the CNTs and the second was to introduce functional groups. TGA was 
used to determine the successful removal of Fe and Co (from Fe-Co/CaCO3). Figure 4.6b 
shows the TGA profile of the as-synthesized and functionalized CNTs. The residual mass 
before functionalization was 13 % which dropped to close to ca. 0 % when the CNTs were 
functionalized with concentrated nitric acid at 50 oC for 12 h. Therefore the majority of the 
impurities in the CNTs were successfully removed and the minority of the residual was Fe 
trapped inside the CNTs. 
0 200 400 600 800
 0
 20
 40
 60
 80
 100
 Temperature (oC)
 W
 ei
 gh
 t (%
 )
 as-synthesized CNTs
 functionalized CNTs
   
Figure 4.6b. TGA profile of the as-synthesized and functionalized CNTs 
58 | P a g e  
 
The thermal stability of the CNTs also decreased (figure 4.6 b) after purification. These 
observations suggest that an increase in the amount of defects created on the CNTs surface 
upon purification aids in the oxidation reaction. Thus, the position of the decomposition peak 
is affected by the amount of residual catalyst in the sample, the defect content created on the 
surface of the CNTs and the amount of amorphous carbon present. 
 The TGA profiles of CSs are presented in Figure 4.6c. The thermal stability of the 
functionalized CSs decreased because the functional groups added to the carbon make them 
more easily oxidized material. 
0 200 400 600 800 1000
 0
 20
 40
 60
 80
 100
 W
 e
 ig
 ht
  
(%
 )
 Temperature (oC)
  as-synthesized CS
  functionalized CS
  
Figure 4.6c. TGA profile of the as-synthesized and functionalized CSs 
4.2.1.5 Raman spectra of the carbon materials 
Raman spectra of CCNFs showing the D and G bands associated with the C-C bonds are 
presented in Figure 4.7. In the Raman spectra, there are two prominent peaks namely the D 
band and the G bands that are associated with carbon materials. The D band is related to the 
disorder structure and attributed to the defects in the curved graphene sheet, the tube ends or 
amorphous carbon. The G band is related to the structural integrity of the sp2-bonded carbon 
atoms in the two dimensional hexagonal lattice, indicating the presence of crystalline 
graphitic carbon.4 The ratio of the intensity of these bands or the ratio of their areas provides 
(ID/IG) crucial information on the graphicity or lack of defects on the carbon materials. Table 
4.3 shows that the peaks in the higher frequency region (at 1562 cm-1) correspond to the G 
band for both the as-synthesized and functionalized CCNFs and peaks at 1435 and 1425  cm-1 
are for the as-synthesized and functionalized CCNFs respectively. 
59 | P a g e  
 
1000 1500 2000
 0
 2000
 4000
 6000
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 Raman shift (cm -1)
  Functionalized CCNF
  As synthesized CCNF
 D-Band G-Band
  
 
1000 1500 2000
 0
 5000
 10000
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 Raman shift (cm -1)
  functionalized CNT
  as-synthesized CNT
 1352 cm -1
 1587 cm -1
 1342 cm -1
 1587 cm -1
   
1200 1600 2000
 0
 2000
 4000
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 Raman shift (cm -1)
  as-synthesized CSs
  functionalized CSs
 1351 cm -1 1582 cm -1
 1352 cm -1 1582 cm -1
  
Figure 4.7. Comparison of the Raman spectra of functionalized and as-synthesized (a) CCNFs, (b) 
CNTs and (c) CSs. 
(a) 
(b) 
(c) 
60 | P a g e  
 
The ratios of the D band to the G band (ID/IG) for the as-synthesized and functionalized 
CCNF were found to be 0.99 and 1.71 respectively. This indicates that functionalization of 
the CCNFs introduced some defects onto the materials.  The Raman spectra for the CNTs and 
CSs were well pronounced as they have distinct D and G bands. The ID/IG ratios for the as-
 synthesized and functionalized CNTs are 2.04 and 2.51 respectively while the ID/IG ratios for 
the as-synthesized and functionalized CSs are 2.7 and 3.02 respectively. This suggests that 
more disorder has been created in the CSs after acid treatment. 
Table 4.3: Raman data for as-synthesized and acid-treated CCNF and CNTs 
Sample ID Peak position (cm-1) 
          D-band                      G-band 
ID/IG 
As-synthesized CCNFs 1425 1562 0.99 
Functionalized CCNFs 1435 1562 1.71 
As-synthesized CNTs 1342 1587 2.04 
Functionalized CNTs 1352 1587 2.51 
As-synthesized CSs 1352 1582 2.70 
Functionalized CSs 1351 1582 3.02 
 
4.2.1.6 Infrared spectroscopy 
Infrared (IR) spectroscopy was used to determine the presence of functional groups on the 
CMs before and after functionalization. Figure 4.8A. shows the peaks at 1000-1100 cm-1 that 
can be attributed to C-O symmetrical stretching, at 1401 cm-1 to O-H bending5 and at 1639 
cm-1 is related to the COOH vibrational mode6. Comparing the IR spectra in Figure 4.8 for 
the three different CMs, significant differences are revealed indicating that functional groups 
have been attached to all the CCNFs, CSs and the CNTs but to different degrees. Two distinct 
peaks are observed at 1424 cm-1 and 1639 cm-1 for CCNFs. The CNTs  shows the 
disappearance of the peak at 1398 cm-1, as well as peaks at 1598 cm-1 and 1734 cm-1 (Figure 
4.8B). The CSs also show differences between the functionalized and the as-synthesized 
materials. A peak is found at 1289 cm-1. In conclusion the functionalization of carbon 
materials has created a change on the surfaces of the different carbon materials. However, 
little else can be added to the information above; it is known that quantification of the IR 
spectra of solid materials e.g. solid carbon materials is not easy. 
61 | P a g e  
 
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
 0.0
 0.2
 0.4
 0.6
 0.8
 1.0
 Wavenumber (cm-1)
 Tr
 an
 sm
 itt
 an
 ce
  
(a.
 u
 )
 1624 cm-1
 1463 cm-1
 (a)
 (b)
 1047 cm-1
  
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
 0.2
 0.3
 0.4
 0.5
 0.6
 0.7
 0.8
 0.9
 1.0
 Wavenumber (cm-1)
 Tr
 a
 n
 sm
 itt
 an
 ce
  
(a.
 u
 )
 1398 cm-1 1593 cm-1
 1734 cm-1
 (a)
 (b)
  
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
 -1.0
 -0.8
 -0.6
 -0.4
 -0.2
 0.0
 0.2
 Wavenumber (cm-1)
 Tr
 a
 n
 sm
 itt
 a
 n
 ce
  
(a.
 u
 )
 1289 cm-1
 (a)
 (b)
  
Figure 4.8. IR spectra of (A) CCNFs , (B) CNTs and (C) CSs with (a) as-synthesized (b) 
functionalized samples are shown in all the three figures 
A 
B 
C 
62 | P a g e  
 
4.2.1.7  Surface area and pore volume measurements 
Nitrogen adsorption at boiling temperature (77 K) is a technique that is used to determine the 
surface area of materials and to characterize their porous structure.7 The surface area and pore 
volume of the catalyst supports are given in Table 4.4. The surface area and pore volume 
increased when the carbon materials were functionalized. This is attributed to the creation of 
defects by the action of acid. Both as-synthesized and functionalized CSs have low surface 
areas and negligible porosity (Table 4.4). The low surface area is a direct consequence of the 
spherical morphology, i.e. the sphere is the geometrical body with lowest exposed surface 
area per unit volume.8  
Table 4.4: Surface area and pore volume of the catalyst supports 
Sample ID BET surface areaa 
(m2/g) 
Pore volume 
(cm3/g) 
As-synthesized CCNFs 89 0.31 
As-synthesized CNTs 80 0.27 
As-synthesized CSs 7 0.02 
CCNFs 94 0.34 
CNTs 90 0.32 
CSs 9 0.03 
AC 688 0.41 
CeO2 76 0.40 
0.5 % Pt/CCNF  113 0.41 
0.5 % Pt/CNT 112 0.40 
0.5 % Pt/CS 9 0.03 
0.5 % Pt/AC 532 
 
0.33 
0.5 % Pt/CeO2 71 0.28 
0.5 % Pt- CeO2/CCNF 115 0.42 
 Spent catalyst 0.5 % Pt- 
CeO2/CCNF 
 
115 
 
0.41 
a  Error bar ? 2%  
4.2.2 Characterization of ceria by TEM 
Ceria was synthesized using the sol-gel method.9 The ceria produced was characterized using 
TEM, in order to determine its morphology. Figure 4.9 shows the TEM image of a ceria 
sample. It was observed that the ceria produced was feather-like with rough edges. This 
property is ideal for ceria?s function as a catalyst support. Mak et al10 described the 
63 | P a g e  
 
morphology of ceria as that of a lamellar meso-structure due to the existence of ?lines? on the 
structure of the ceria particles, as can also be seen in Figure 4.9. 
 
Figure 4.9. TEM image of ceria 
4.2.3 Characterization of activated carbon and titania by TEM 
Activated carbon (AC) and titania (Degussa P 25) were used as catalyst supports in this 
study. They were used as purchased without further treatment. Their morphology was 
characterized by TEM. Figure 4.10. shows the TEM images of AC and titania. The 
information that can be obtained from TEM of AC is its morphology (solid carbonaceous 
material); while titania possess cube like particles. 
   
Figure 4.10. TEM images of (a) AC and (b) titania 
 
(a) (b) 
 
4.3 Analysis of the Pt supported catalysts
 Platinum was deposited on to the support materials using the polyol method. The synthesis 
method involves the reaction of hexachloroplatinic acid (Pt precursor) with the support 
materials in ethylene glycol (EG).
 reducing species. The reducing species (such as CH
 metal particles.11 
4.3.1  Mechanism of polyol synthesis
 The mechanism of polyol synthesis is illustrated in cartoon fo
 materials (Figure 4.11a) were first exposed to an oxidation environment where negatively 
charged groups are attached to the carbon (Figure 4.11b). The Pt
 functional sites via electrostatic attract
 temperature EG decomposes to form reducing species which in turn reduces Pt
 metallic grains formed further agglomerate to form nanoparticles (Figure 4.11d).
 Figure 4.11. Schematic representation of the mechanism behind the polyol synthesis method 
The mechanism for the deposition of Pt on other supports (ceria, AC, titania) is the same 
except that the reaction does not require an acid treatment step.
  
 
 
 When heat is supplied to EG, it decomposes to form 
3CHO) then reduce the metal ions to 
 
rm in Figure 4.13. The carbon 
4+
  ions then diffused to these 
ion to form nucleation sites (Figure 4.11c). At high 
 
64 | P a g e  
4+
  to Pt0. The 
 
 
 
65 | P a g e  
 
4.3.2 Formation of Pt: UV-vis spectroscopy 
The UV-vis spectra of H2PtCl6 in ethylene glycol was recorded and the reduction process was 
monitored through measurement of the Pt absorbance at different times (Figure 4.12). The 
solution of a mixture of hexachloroplatinic acid, ethylene glycol and water exhibited a peak 
at 260 nm (Figure 4.12a). For a 0.5 % Pt loading, the solution was placed in a microwave 
oven for 1 minute and the solution analyzed by UV-vis spectroscopy; the peak intensity 
decreased (Figure 4.12b). The solution was then exposed to another 1 minute in the 
microwave oven. The spectrum recorded showed that the Pt peak at 260 nm disappeared 
completely (Figure 4.12c). Luo and Sun12 attributed the disappearance of the Pt peak in a 
related study to the reduction of the PtCl62-.  This indicates the complete reduction of Pt+4 to 
Pt0. Therefore 2 minutes was enough to reduce Pt ions and Pt nanoparticles in the samples 
under study. 
200 300 400
 -0.5
 0.0
 0.5
 1.0
 1.5
 2.0
 2.5
 3.0
 3.5
 Wavelength (nm)
 Ab
 so
 rb
 a
 n
 ce
 a
 b
 c
  
Figure 4.12. UV-vis spectra of 0.5 % loading of Pt (a) before reduction, (b) after 1 minute in the 
microwave oven and (c) 2 after minutes in the microwave oven. 
4.4 0.5 % Pt loaded catalysts. 
Platinum was loaded on the as-synthesized and functionalized carbon materials (CCNFs, CSs 
and CNTs), activated carbon (AC), ceria and titania. The platinum supported catalysts were 
66 | P a g e  
 
characterized by TEM. These catalysts were denoted as Pt/CCNF, Pt/CNT, Pt/CS, Pt/AC, 
Pt/CeO2 and Pt/TiO2.  
4.4.1 TEM analysis for the 0.5 % Pt loaded on to the as-synthesized CMs 
Figure 4.13 shows the TEM images of Pt loaded onto the as-synthesized CCNFs, CSs and 
CNTs. From the TEM images it can be observed that the Pt nanoparticles were well dispersed 
despite the occurrence of some impurities in the CCNF (Figure 4.13a). A possible 
explanation for the good deposition of Pt is that the materials have a highly disordered 
surface as shown from the TGA plot in Figure 4.6a. On the other hand the TEM images of the 
as-synthesized CNTs and CSs showed that Pt was barely visible. This indicates that some of 
the Pt nanoparticles were not adsorbed onto as-synthesized CNTs and CSs. This observation 
was not a surprise because the samples of the filtrates collected for Pt/CCNF, Pt/CS and 
Pt/CNT showed the existence of dark solutions for Pt/CS and Pt/CNT   (Figure 4.14b and c). 
A possible explanation for this is that Pt nanoparticles (black) are in solution because the 
attraction between carbon and Pt is low as the carbon materials are hydrophobic in nature. An 
almost colourless solution for Pt/CCNF (Figure 4.14a) is observed implying that most of the 
Pt nanoparticles have been adsorbed onto the CCNF.  
     
a b
 
Figure 4.13. Pt loaded to the as-synthesized (a) CCNFs, (b) CNTs and (c) CSs
 Figure 4.14. Filtrates obtained from (a) Pt/CCNF, (b) Pt/CNT and Pt/CS 
4.4.2 TEM analysis for the 0.5
 Representative TEM micrographs of 0.5
 histograms) prepared by microwave heati
 observed that the different supports have different sizes of Pt. Titania has the smallest particle 
size of Pt particles with a mean of 1.6 nm and AC has the largest particle size of Pt, with a 
mean of 2.9 nm. The histograms indicate that Pt has a narrow distribution range on the 
various supports. A summary table with mean sizes of Pt on the various supports is presented 
in Table 4.5. 
 
c 
 
 
 
 % Pt loaded catalysts (polyol method)
  % Pt supported catalysts (and their corresponding 
ng methods are shown in Figure 4.15. It can be 
67 | P a g e  
 
 
68 | P a g e  
 
  
1.0 1.5 2.0 2.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
%
 Particle size (nm)
 mean=1.8 nm
  
  
1.5 2.0 2.5 3.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.3 nm
  
  
2.0 2.5 3.0 3.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.6 nm
  
ba
 fe
 dc
69 | P a g e  
 
  
2.0 2.5 3.0 3.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.9 nm
  
  
2.0 2.5 3.0 3.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.7 nm
  
  
1.0 1.5 2.0 2.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=1.6 nm
  
Figure 4.15. TEM images and size distributions of 0.5 % Pt supported on (a) and (b) CCNF; (c) and 
(d) CNT; (e) and (f) CS; (g) and (h) AC; (i) and (j) CeO2;  (k) and (l) TiO2. 
 
j
 hg
 i
 lk
70 | P a g e  
 
Table 4.5: Summary table of the mean particle size of catalyst with different Pt loading. 
Catalyst Mean particle size (nm) 
     0.5 % Pt loading                  1 % Pt loading                   5 % Pt loading 
Pt/CCNF 1.8 2.5 3.8 
Pt/CNT 2.3 3.0 4.3 
Pt/CS 2.6 3.3 4.6 
Pt/AC 2.9 3.6 6.9 
Pt/CeO2 2.7 3.4 5.0 
Pt/TiO2 1.6 2.3 3.3 
Error bar= 1 % 
4.4.3 Determination of presence of Pt in the catalyst. 
The EDS analysis confirmed the presence of platinum in the catalyst sample 0.5 % Pt/CCNF. 
Figure 4.16 shows the EDS spectrum of 0.5 % Pt/CCNF. The copper that is observed in the 
spectrum is due to the copper grid.  
    
Figure 4.16. EDS spectra of Pt/CCNF 
The Pt quantification was achieved by ICP AES. The results of the analysis ascertained the 
loading of Pt in the catalysts. Table 4.6 shows the metal loading in the catalysts and that they 
agree with the expected loadings. This contrast with the Pt loading on the as-synthesized 
CMs. 
 
71 | P a g e  
 
Table 4.6: Pt loading in the catalysts obtained from ICP AES analysis 
Catalysts Theoretical  Pt/CCNF Pt/CNT Pt/CS Pt/AC Pt/CeO2 Pt/TiO2 
Pt loading (%) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 
Pt loading (%) 1.0 1.0 1.1 1.0 1.2 1.0 1.0 
Pt loading (%) 5.0 5.1 5.0 5.0 5.1 5.1 5.0 
 
4.4.4  Surface area and pore volume measurements of 0.5% Pt catalysts 
The BET surface areas were measured for the 0.5 % Pt supported catalysts and the results are 
presented in Table 4.4. The BET surface areas have increased with Pt loading for CCNFs, 
CNTs and CSs. This is attributed to the absence of micropores which can get blocked and 
reduce the BET surface area. Pt/CS with low surface area and low total pore volume did not 
experience any appreciable change upon Pt introduction. The BET surface area of ceria and 
AC decreased with Pt introduction. This is attributed to a partial pore blockage by the Pt 
particles. 
4.5 1 % Pt loaded catalysts 
The Pt nanoparticles were synthesized using the microwave polyol method and Pt was 
successfully loaded onto five different catalyst supports (CNTs, CSs, AC, ceria and titania). 
Figure 4.17 shows the TEM images of the Pt supported on the different catalyst supports. The 
mean sizes are 2.5, 3.0, 3.3, 3.6, 3.4 and 2.3 nm for Pt supported on CCNF, CNT, CS, CeO2, 
AC and titania respectively. The microwave heated polyol synthesis is hence effective in 
depositing small platinum particles on the support. Data are shown in Table 4.5. In all cases 
the Pt particle size has increased with loading. 
   
2.0 2.5 3.0
 0
 5
 10
 15
 20
 25
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.5 nm
  
b a 
72 | P a g e  
 
 
 
2.0 2.5 3.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.5 nm
  
  
2.0 2.5 3.0 3.5 4.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.0 nm
  
 
2.5 3.0 3.5 4.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.3 nm
  
g 
e f 
h 
d c 
73 | P a g e  
 
 
3.0 3.5 4.0 4.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.6 nm
  
 
2.5 3.0 3.5 4.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.4 nm
  
  
1.5 2.0 2.5 3.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=2.3 nm
  
Figure 4.17. TEM images and size distributions of 1 % Pt supported on (a) and (b) CCNF prepared 
by conventional heating and the rest were  prepared by microwave heating; (c) and (d) CCNF; (e) and 
(f) CNT; (g) and (h) CS; (i) and (j) AC; 
 
(k) and (l) CeO2; (m) and (n) TiO2. 
n 
l 
j i 
k 
m 
74 | P a g e  
 
4.5.1 Microwave versus conventional heating 
Different heating methods were used to prepare 1 and 5 % loading of Pt/CCNFs. A summary 
of the comparison between particles formed using either microwave or conventional heating 
method is presented in Table 4.7. It can be seen that the conventional method and the 
microwave heating method both produce similar Pt size distributions. This is surprising since 
in the conventional method, stirring is continuous until the experiment is performed while in 
the microwave oven there is no stirring. Despite the lack of differences, the microwave 
method offers uniformity, speed, energy efficiency and implementation simplicity.13 
 
Table 4.7: Comparison of the mean particle size obtained using different heating method  
Heating method Pt loading (%) Mean particle size (nm) 
Microwave 1 
5 
2.5 
3.8 
Conventional 
(reflux) 
1 
5 
2.5 
3.6 
Error bar ? 0.8 nm  
4.6 5 % Pt loaded catalysts 
Platinum was deposited on CCNF, CNT, CS, AC, ceria and titania using the polyol method. 
These samples have a metal loading of 5 %. TEM micrographs of the supported Pt catalysts 
are presented in Figure 4.18. The corresponding histogram are also shown in Figure 4.18, 
they show a narrow distribution of Pt on the various supports (see also Table 4.5). The 
comparison of the heating methods is also given for Pt/CCNFs. The conventional heating has 
a mean Pt size of 3.6 nm whilst the microwave heating has a mean Pt size of 3.8 nm. In 
conclusion microwave heating is a better choice as it produces roughly the same size of 
particles as conventional heating at a faster rate with energy efficiency. 
75 | P a g e  
 
 
3.0 3.5 4.0 4.5
 0
 5
 10
 15
 20
 D
 ist
 rib
 u
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.6 nm
  
 
2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.8 nm
  
  
3.5 4.0 4.5 5.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=4.3 nm
  
b 
c d 
a 
f e 
76 | P a g e  
 
  
4.0 4.5 5.0 5.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=4.6 nm
  
    
6.0 6.5 7.0 7.5
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=6.9 nm
  
  
4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=5.0 nm
  
l 
j i 
h g 
k 
77 | P a g e  
 
  
2.5 3.0 3.5 4.0
 0
 5
 10
 15
 20
 D
 is
 tri
 bu
 tio
 n
  
(%
 )
 Particle size (nm)
 mean=3.3 nm
  
Figure 4.18. TEM images and size distributions of 5 % Pt supported on (a) and (b) CCNFs prepared 
by conventional heating and the rest were  prepared by microwave heating; (c) and (d) CCNFs; (e) 
and (f) CNTs; (g) and (h) CSs; (i) and (j) AC; 
 
(k) and (l) CeO2; (m) and (n) TiO2.  
4.6.1 Effect of loading on the particles size 
There is a general trend that can be observed in Table 4.5 in terms of the relationship of 
particle size to metal loading i.e. an increase in metal loading results in an increase in the size 
of the Pt nanoparticles. The mean Pt particle size followed a similar trend, for example, 0.5 % 
Pt/CCNFs have a mean size of 1.8 nm while the 5 % Pt/CCNF had a mean size of 3.8 nm.  
Knupp et al5 obtained a similar trend for the effect of increasing metal loading on the size of 
Pt particles and they suggested that it was due to the fact that when the loading is increased, 
agglomeration is more apparent and large particles begin to form. The mean Pt nanoparticle 
size thus gets larger.  
4.6.2 Temperature programmed reduction 
Temperature programmed reduction (TPR) analysis was done prior to any further reduction 
treatment to determine whether the Pt catalyst (Pt/CS, Pt/CCNF and Pt/CNT) was already in 
its reduced state. The TPR profiles of Pt/CS, Pt/CCNF and Pt/CNT (5 % loading) after 
synthesis and drying are depicted in Figure 4.19. Plomp and co-workers14 state that the 
reduction of Pt occurs between 177 and 302 oC. Figure 4.19 clearly showed that there is no 
peak in that temperature range. This indicates that Pt on CSs, CCNFs and CNTs were 
successful reduced using the microwave assisted polyol synthesis. The profile at temperature 
above 500 oC is ascribed to the gasification of the supports. The gasification of the support 
n m 
78 | P a g e  
 
can result in the formation of methane. Methane is formed under the hydrogenation 
conditions when temperatures are above 427 oC.15 At high temperature, methane could 
decompose to generate carbon deposits on the CCNFs. This is due to the fact that the CCNFs 
were synthesized at low temperature (250 oC). Thus a high temperature could result in the 
graphitization of the materials. TEM was used to confirm the material deposited on to the 
CCNF was carbon as shown in Figure 4.20. 
 
0 200 400 600 800 1000
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 Temperature (oC)
 5% Pt/ CS
  
0 200 400 600 800 1000
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 Temperature (oC)
 5% Pt/CCNF
  
 
0 200 400 600 800 1000
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 Temperature (oC) 
5% Pt/CNT
  
Figure 4.19. TPR profile of (a) Pt/CS, (b) Pt/CCNF and (c) Pt/CNT 
From the TEM image, the morphology of the deposited carbon material seems to suggest the 
formation of carbon spheres which are accreted.  
79 | P a g e  
 
  
Figure 4.20. TEM image of Pt/CCNF (a) before and (b) after TPR analysis 
TPR was also used to obtain information about the onset of reduction of the ceria and the 
Pt/CeO2. The significance of the information is to help to control the eventual hydrogenation 
parameters of the catalyst. Figure 4.21 shows the TPR profiles of ceria and Pt/CeO2. From 
Figure 4.20, ceria shows a peak at 475 oC which corresponds to the reduction of ceria 
particles from Ce4+ to Ce3+. This is in agreement with studies reported by Zhang and co-
 workers16 who stated that the reduction of ceria occurs at 475 oC. When Pt was introduced on 
to the surface of ceria, the reduction of ceria shifted to lower temperatures (367 oC). This 
indicates that the reduction of ceria is effectively promoted by Pt. This is attributed to the 
ability of Pt to activate H2 and spill it over to the support. For catalytic purposes, the working 
temperature should be below 300 oC to avoid the effect of this CeO2 reduction. 
0 100 200 300 400 500 600 700 800 900
 Temperature (oC)
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 5% Pt/CeO2
 CeO2
  
Figure 4.21. H2-TPR profile of Pt/CeO2 and CeO2 
b a 
80 | P a g e  
 
4.6.3 X-ray diffraction studies on Pt supported catalysts 
X-ray diffraction (XRD) was done to determine the phases in the Pt supported catalysts. XRD 
spectra of the standard Pt peaks are located at 39o (111), 46o (200), 67o (220) and 81o (311).17 
The peaks indicate that the Pt nanoparticles produced are face centred cubic. The XRD 
patterns for the CM and Pt/CM are presented in Figure 4.22. 
30 60 90
 0
 1000
 2000
 3000
 Pt
  
(31
 1)
 Pt
  
(22
 0)
 Pt
  
(20
 0)In
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (o)
  CCNF
  Pt/CCNF
 Pt
  
(11
 1)
  
30 60 90
 0
 3000
 6000
 Pt
 (31
 1)
 Pt
 (22
 0)
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (o)
  CS
  Pt/CS
 C(002) Pt(111)
 Pt
 (20
 0)
  
30 60 90
 0
 3000
 6000
 Pt
 (20
 0)
 Pt
 (31
 1)
 Pt
 (22
 0)P
 t(1
 11
 )
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (o)
  Pt/CNT
  CNT
 C(
 00
 2)
  
Figure 4.22. XRD patterns of (a) CCNF and Pt/CCNF, (b) CS and Pt/CS and (c) CNT and Pt/CNT 
The CCNF is amorphous since it did not show a carbon graphite peak at 25.5 o (Figure 4.22a) 
while both CS and CNT possessed this peak at 25.5o indicating that they are more crystalline. 
All the Pt peak positions suggest that it is crystalline with a face centred cubic structure.  
 
a b 
c 
81 | P a g e  
 
XRD spectra were also recorded for AC, ceria, titania, Pt/AC, Pt/CeO2 and Pt/TiO2. The 
XRD spectra are presented on Figure 4.23. 
30 60 90
 0
 8000
 16000
 Pt(311)Pt(220
 Pt(200)
  
In
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (o)
  Pt/AC
  AC
 Pt(111)
  
30 60 90
 0
 700
 1400
 Ce
 O
 2(3
 31
 )
 Ce
 O
 2(4
 22
 )
 Ce
 O
 2(4
 00
 )
 Ce
 O
 2(3
 11
 )
 Ce
 O
 2(2
 20
 )
 Pt
 (11
 1)
 Ce
 O
 2(2
 00
 )
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (oC)
  Pt/CeO2
  CeO2
 Ce
 O
 2(1
 11
 )
  
30 60 90
 0
 2000
 4000
 Ti
 O
 2(2
 20
 )
 Ti
 O
 2(1
 16
 )
 Ti
 O
 2(1
 18
 )
 Ti
 O
 2(2
 11
 )
 Ti
 O
 2(1
 05
 )
 Ti
 O
 2(2
 00
 )
 Ti
 O
 2(0
 04
 )
 In
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (oC)
  Pt/TiO2
  TiO2
 Ti
 O
 2(1
 01
 )
  
Figure 4.23. XRD patterns of (a) AC and Pt/AC, (b) CeO2 and Pt/CeO2 and (c) TiO2 and Pt/TiO2 
a 
b 
c 
 
A graphite peak is observed at around 25.5 
The characteristic diffraction peaks of the face centred cubic crystalline Pt in the Pt/AC 
catalyst, namely (111), (200) and (220) in the region of 39
 presence of Pt in metallic form.
 Pt. Only one peak of Pt can be observed (Figure 4.2
 in the face centred cubic crystalline in Pt/CeO
 essentially the same as that of the TiO
 line of Pt for Pt/TiO2 indicates that Pt is in a high degree of dispersion.
 4.6.4 Particle size from XRD
 The particle sizes of 5 % Pt catalysts were calculated using the Scherrer equations. The 
Scherrer equation is given below:
 where L is the average particle size, 
maximum of the peak position and 
4.8 shows the particle size obtained from both TEM and XRD for the 5
 materials. The results of particle size from the TEM study are in agreement with what can be 
observed from the XRD patterns. The broad peaks o
 that the Pt particles have a small size (4.4 nm) and the narrow peaks on the Pt/AC (Figure 
4.22a) indicates a big particle size (8.2 nm)
 Table 4.8: Summary table of the mean particle size of catalyst with different P
 Catalyst 
Pt/CCNF 
Pt/CNT 
Pt/CS 
Pt/AC 
Pt/CeO2 
Pt/TiO2 
Error bar= 1 % 
oC in the XRD spectrum of AC (Figure 4.2
 o
 , 46o and 67
 18
  Ceria did not change its cubic structure in the presence of 
3b) at Pt(111) indicating that Pt is present 
2. The XRD patterns of the Pt/TiO
 2 sample (Figure 4.23c). The absence of the diffraction 
19
   
 
  
 
? is the sources wavelength, B is the full width at half 
? is the angle at which the diffraction peak arises. Table 
n the Pt/CCNF (Figure 4.21a), indicates 
 
t loading.
 Mean particle size (nm) for 5 % Pt loaded on supports
                   TEM                                            XRD
 3.8 
4.3 
4.6 
6.9 
5.0 
3.3 
82 | P a g e  
3a). 
o
  demonstrates the 
2 catalyst was 
 % Pt loaded 
 
 
 
4.1 
4.5 
4.9 
8.2 
5.3 
- 
83 | P a g e  
 
4.7 Ceria supported on carbon materials 
A Pt-CeO2/CM catalyst was made in two steps. The first step entailed depositing ceria on to 
carbon materials and the second step was the addition of Pt to CeO2/CM. The synthesis 
method involves the reduction of cerium nitrate using ethylene glycol as a solvent and 
reducing agent, while sodium acetate was used as the stabilizing agent. Ceria particles were 
deposited on the CM with loadings of 5 % and 10 %. The TEM images for the CeO2/CM are 
shown in Figure 4.24. Ceria particles are well distributed on the CCNF, CS and CNT surfaces 
as shown in Figure 4.24. This indicates that the polyol method of synthesis is quite good for 
ceria deposition. The average particle size of ceria particles on CeO2/CCNF is 4.8 nm, 
CeO2/CNT is 5.3 nm and CeO2/CS is 5.5 nm.  
  
 
 
Figure 4.24. TEM images of (a) CeO2/CCNF, (b) CeO2/CS and (c) CeO2/CNT 
a b 
c 
84 | P a g e  
 
The percentage of ceria loaded on to the carbon materials was confirmed by TGA. Figure 
4.25 shows the TGA profiles of CCNFs loaded with 5 % and 10 % ceria. The residual 
amounts of ceria were 5.2 % and 10.3 % respectively. The loading of ceria on the CNTs and 
CSs are presented in Table 4.9. The loading of ceria was successfully determined and the 
values are very close to the expected loadings. 
0 200 400 600 800 1000
 0
 20
 40
 60
 80
 100
 W
 e
 ig
 ht
  
(%
 )
 Temperature (?C)
 5.2%
  
0 200 400 600 800 1000
 0
 20
 40
 60
 80
 100
 W
 e
 ig
 ht
  
(%
 )
 Temperature (?C)
 10.3 %
  
Figure 4.25. TGA profile of 5 % and 10 % loading of ceria on CCNF. 
 
Table 4.9: Ceria loading obtained using TGA 
Material Residual amount of ceria (%) 
           Theoretical                             Experimental 
CeO2/CS 5.0 
10.0 
5.1 
10.2 
CeO2/CNT 5.0 
10.0 
5.0 
10.1 
 
4.7.1 XRD profile of ceria supported on carbon materials 
The XRD technique was used to confirm the presence of ceria in the carbon materials and 
also to check if it retained the fluorite structure. The peaks in the region 28.5o (111), 32.9o 
(200) and 56.3o (311) can be indexed for CeO2 with a fluorite structure.18 Figure 4.26 shows 
the XRD patterns of ceria and ceria supported on carbon materials. It can be clearly seen that 
there is no shift in any of the diffraction peaks of ceria at all compositions indicating that 
85 | P a g e  
 
carbon materials have no effect on the crystallographic orientations of ceria particles. 
Because of the nature of CCNFs, the peaks of ceria are not well pronounced. In conclusion, 
ceria was successful deposited on the carbon materials and it was in its fluorite structure. 
30 60 90
 0
 1000
 2000
 3000
 4000
 (d)
 (c)
 (b)
 CeO2/CS
 CeO2/CNTI
 n
 te
 n
 si
 ty
  
(a.
 u
 )
 2 Theta (o)
 CeO2
 CeO2/CCNF
 (a)
  
Figure 4.26. XRD patterns of (a) CeO2/CCNF, (b) CeO2, (c) CeO2/CNT and (d) CeO2/CS 
4.7.2 Platinum deposited onto CeO2/CM 
Platinum (0.5 %) was deposited onto the CeO2/CM using the polyol method. The platinum 
precursor (H2PtCl6) was reduced with ethylene glycol at temperatures of 160 oC and the Pt 
nanoparticles formed were deposited onto the support (CeO2/CM). TEM analysis was used to 
determine the morphology of Pt-CeO2/CM catalyst formed. Figure 4.27 shows the TEM 
images of the 0.5% Pt-CeO2/CM catalysts. 
  
a b 
86 | P a g e  
 
 
Figure 4.27. TEM images of (a) Pt-CeO2/CCNF (b) Pt-CeO2/CNT and (c) Pt-CeO2/CS 
It can clearly be seen from Figure 4.26 that ceria is well distributed across the entire surface of 
CCNFs, CNTs and CSs though it is difficult to locate the Pt nanoparticles. EDS was used to show that 
Pt was present in the catalysts. Figure 4.28 shows the EDS spectrum of Pt/CCNF 
 
Figure 4.28. EDS spectra of Pt-CeO2/CCNF 
The copper that is observed in the spectrum is due to the copper grid. Pt quantification was 
achieved by ICP AES. The results are shown in Table 4.10. 
 
 
c 
87 | P a g e  
 
Table 4.10: Pt loading in the catalysts 
Catalyst Pt loading (%)a 
Pt- CeO2/CCNF 0.50 
Pt- CeO2/CNT 0.50 
Pt- CeO2/CS 0.51 
a
  theoretical= 0.5 % Pt 
4.8 Catalytic activity 
The hydrogenation of ethylene over the Pt catalyst supported on carbon materials (CNTs, 
CCNFs, CSs and AC), oxides (TiO2 and CeO2) and CeO2/CM was performed at 30 oC. The 
hydrogenation activity was first tested on the supports to check the inertness of the supports. 
The results of the experiments showed that all the supports showed no activity for the 
hydrogenation of ethylene. 
4.8.1 Effect of functionalization 
The activity of the as-synthesized CCNF and the functionalized CCNF loaded with 1 % Pt 
was tested for the hydrogenation of ethylene and the results are presented on Figure 4.29. The 
functionalized CCNF gave a 100 % conversion indicating that all the ethylene was converted 
to ethane while the conversion (67 %) of the as-synthesized CCNF decreased with time on 
stream as shown in Figure 4.29a. Characterization of the spent catalyst by TEM revealed that 
the as-synthesized CCNFs sintered rapidly. Figure 4.30a show the TEM image of the spent 
catalyst (Pt supported on as-synthesized CCNF). There is evidence of Pt agglomerates which 
are located at the curves of the CCNFs. 
88 | P a g e  
 
0 50 100 150 200 250 300
 0
 20
 40
 60
 80
 100
 Time (min)
 Co
 n
 ve
 rs
 io
 n
  
(%
 ) (a)
 (b)
  
Figure 4.29. Ethylene conversion over Pt supported on (a) as-synthesized CCNFs and (b) 
functionalized CCNFs at 30 oC. [H2/C2H4 = 2; flow rate = 100 mL/min; catalyst mass = 0.1 g] 
  
Figure 4.30a. TEM images of the Pt/as-synthesized CCNFs  (a) before and (b) after hydrogenation of 
ethylene  
The possible explanation for the rapid sintering of the Pt on the as-synthesized CCNFs relates 
to the lack of strong anchoring of the Pt on the as-synthesized CCNFs. As a result the Pt 
nanoparticles move freely and then aggregate. The view about no strong anchoring is 
supported by reports from Yang et al20, who indicated that the as-synthesized CNTs do not 
possess a large quantity of functional groups on their surface. There was no observable TEM 
change on the size of the Pt particles on the spent catalyst of Pt/functionalized CCNFs 
(Figure 4.30b).    
a b 
89 | P a g e  
 
 
      
Figure 4.30b. TEM images of (a) before and (b) after hydrogenation of ethylene using 
Pt/functionalized CCNF 
The initial and final activity of Pt supported on the as-synthesized CNT and CS is shown on 
the Table 4.11. 
Table 4.11: Conversion rates of the 1 % Pt supported for the as-synthesized and 
functionalized CNTs and CSs in 300 mins 
Catalyst Conversion (%) 
                   Initial                                          Final 
Pt on as-synthesized CNT 22 0 
Pt on functionalized CNT 100 100 
Pt on as-synthesized CS 31 0 
Pt on functionalized CS 100 100 
The low initial activity for both Pt supported on as-synthesized CNTs and CSs is attributed to 
poor deposition of Pt during synthesis (see Figure 4.13). This was caused by lack of 
anchoring sites on the surface of CNTs and CSs. The conversion decreased to zero in 300 
mins due to sintering. When there is no strong anchoring of Pt nanoparticles, they easily 
move and agglomerate. The decrease in conversion can also be due to metal leaching. In 
conclusion functionalization of carbon materials is crucial as it leads to strong anchoring of 
the active Pt phase.  
a b 
90 | P a g e  
 
4.8.2 Effect of metal loading  
A series of Pt/CCNF catalysts were prepared with different Pt loadings (0.5, 1, 5 %). Figure 
4.31 shows the ethylene conversion as a function of time for the Pt/CCNF catalysts. The 5 % 
Pt loaded catalyst showed 100 % conversion for the entire catalytic reaction. The 1 % loaded 
Pt catalyst gave a 100 % conversion for 3500 mins and then it began to decrease. The activity 
of 0.5 % Pt/CCNF catalyst was the lowest with a 80 % initial conversion. Generally the 
higher the loading implies more catalyst particles to interact with the reactants and thus the 5 
% Pt loaded material has the highest activity as compared to the 1 % and 0.5 % Pt loaded 
CCNFs. The deactivation of the reaction as time increased might be due to coke deposition or 
sintering. The smaller the particles (0.5 % Pt) the more easily they can be covered with the 
coke.  
0 2000 4000 6000 8000 10000
 0
 20
 40
 60
 80
 100
 Time (min)
 Co
 n
 ve
 rs
 io
 n
  
(%
 )
 (c)
 0
 20
 40
 60
 80
 100
 (a)
 (b)
  
Figure 4.31. Effect of Pt loading on the conversion of ethylene, (a) 0.5 %, (b) 1 %, (c) 5 % [H2/C2H4 
= 2; flow rate = 100 mL/min; catalyst mass = 0.1 g] 
The same trend was observed with Pt/CNT and Pt/CS catalysts; increasing Pt loading resulted 
in an increase in the rate of hydrogenation. Table 4.12 shows the conversion of ethylene to 
ethane using different Pt/CNT and Pt/CS catalysts. In both catalysts, the 5 % Pt loading 
remain unaltered for the duration of the experiment. The decrease in metal loading resulted in 
decrease in the activity this was attributed to a small amount of Pt particles that get in contact 
with the reactants. 
 
91 | P a g e  
 
Table 4.12: Conversion of ethylene using different loadings of Pt on CNTs and CSs 
Catalyst Pt loading (%) Conversion (%) 
             Initial                             Final 
Pt/CNT 5 
1 
0.5 
100 
100 
68 
100 
81 
50 
Pt/CS 5 
1 
0.5 
100 
100 
65 
100 
78 
43 
 
4.8.3 Effects of increasing the ratio of H2:C2H4  
The ratio of H2 to C2H4 was increased to 5:1 and the results are shown in Table 4.13. 
Table 4.13: Effect of increasing flow rate of H2:C2H4. (H2/C2H4 = 5) 
Conversion (%) 
0.5 % Pt/CCNF 0.5 % Pt/CNT 0.5 % Pt/CS 
100 100 100 
 
Increasing the flow of hydrogen caused an increase in the stability of the reaction. (Figure 
4.30, and Table 4.13). This was explained by Neurock and Mei21, who reported that when the 
partial pressure of hydrogen is greater than that of ethylene, the rate of decomposition of 
ethylene is slower than ethylene hydrogenation. This leads to a very slow rate of formation of 
ethylidyne and CHx intermediates which hinders the hydrogenation of ethylene and therefore 
the stability of the reaction. 
4.9 Effect of catalyst supports 
A range of supports (Pt/CCNF, Pt/CNT, Pt/CS, Pt/AC, Pt/CeO2 and Pt/TiO2) were used for 
the hydrogenation of ethylene. The results of the experiment are depicted in Figure 4.32. 
92 | P a g e  
 
0 2000 4000 6000 8000 10000
 0
 20
 40
 60
 80
 100
 Time (min)
 Co
 n
 ve
 rs
 io
 n
  
(%
 )
  0.5% Pt/CCNF
  0.5% Pt/TiO2
  0.5% Pt/CeO2
  0.5% Pt/AC
  0.5% Pt/CNT
  0.5% Pt/CS
  
Figure 4.32. Effects of the supports on the conversion of ethylene.
   
[H2/C2H4 = 2; Flow rate = 100 
mL/min; Catalyst mass = 0.1 g] 
It can be observed from Figure 4.32 that titania was the best support. Pt/TiO2 had an initial 
activity of 72 % whilst Pt/CCNF (70 %), Pt/CNT (68 %), Pt/CS (65 %), Pt/AC (62 %), 
Pt/CeO2 (60 %). These activities are good considering that only 0.5 % loading of Pt is being 
used. Another interesting feature that can be obtained from Figure 4.32, is that it takes a lot of 
time for the catalyst to start to deactivate. Deactivation starts at ca. 3000 mins for Pt/CeO2 
and Pt/AC whilst Pt/CCNF, Pt/CNT and Pt/CS extend up to ca. 4000 mins. The high activity 
of Pt/TiO2 can be attributed to the small particle sizes of Pt formed on its surface (Table 4.4) 
and also the high dispersion noted from the XRD data. Amongst the carbon materials, the 
CCNFs was the best support. This can be explained in terms of the size of Pt nanoparticles. 
The small particle size of Pt leads to an enhancement of its catalytic properties22 as large 
fractions of the active metal atoms are on the surface and thus are accessible to reactant 
molecules and available for catalysis.23 The Pt supported on carbon materials (CCNFs, CNTs, 
CSs) had a higher rate of reaction than ceria and AC because they possess mesopores which 
are suitable for catalytic reactions. The relatively lower activity of Pt/AC can be attributed to 
the existence of micropores. Bitter,24 reported that microporosity hampers fast diffusion of 
reactants and products to and from active sites making these less productive. The stability of 
the Pt supported catalysts can be attributed to strong anchoring of the Pt nanoparticles on the 
different supports. In other words the method of depositing Pt on the support (polyol method) 
was effective in ensuring that Pt is firmly held on the support. The deactivation which 
93 | P a g e  
 
occurred may be a result of sintering as well as the formation of carbon deposits which in 
turn block the active sites of Pt.  
4.9.1 Effect of adding ceria on the Pt/CM catalyst 
Ceria (5 %) was added to the Pt/CM to make Pt-CeO2/CM. This was done in order to 
improve the surface area of the active phase. When the surface area of the active phase 
increases, the rate of reaction will also increase. The results for the hydrogenation of ethylene 
using Pt-CeO2/CM catalyst are presented in Figure 4.33. The addition of 5 % ceria onto 
Pt/CM caused an increase in the rate of reaction. Figure 4.33 shows that when ceria is added 
to the CCNFs it gives a have higher activity that when ceria is absent. This was due to a ceria 
effect. 
0 2000 4000 6000 8000 10000
 0
 20
 40
 60
 80
 100
  Pt/CCNF
  Pt-CeO2/CCNF
  Pt/CNT
  Pt-CeO2/CNT
  Pt/CS
  Pt-CeO2/CS
 Time (min)
 Co
 n
 ve
 rs
 io
 n
  
(%
 )
  
Figure 4.33. Effect of adding ceria to the Pt/CM catalyst.
   
[H2/C2H4 = 2; flow rate = 100 mL/min; 
catalyst mass = 0.1 g] 
The catalysts were stable for the entire hydrogenation reaction. The stability of the ceria 
based catalyst was also attributed to the fact that ceria suppresses the sintering of the active 
metal25 and also preserves the catalyst surface area26. The catalyst surface area of the 0.5 % 
Pt-CeO2/CCNF and the BET surface area (Table 4.4) did not change on the spent catalyst. 
The proposed mechanism of suppressed sintering of Pt particles is shown in Figure 4.34. The 
ceria particles are thought to be situated between the Pt nanoparticles. It is therefore difficult 
for the Pt nanoparticles to agglomerate. The TEM image in Figure 4.35 shows the 0.5 % Pt-
 CeO2/CCNF catalyst in which Pt is situated between the ceria particles. Figure 4.35 shows 
that both ceria and Pt particles are on the surface of CCNF. 
 
Figure 4.34. Cartoon showing a possible mechanism for suppression of Pt sintering. (CM stands for 
the carbon materials, CeO2 represent ceria particles and 
 
Figure 4.3
 4.9.2 Effect of temperature
 Figure 4.36 displays the effect of temperature on the activity of a 0.5
 The temperature increase caused a small increase in the initial rate of reaction. A reaction 
temperature of 30 oC for the hydrogenation of ethylene over Pt/CCNF catalyst gave results 
indicative of a moderately stable catalyst. The final
 was low, presumably due to a sintering effect which is more pro
 temperatures. Mondal reported the same results for a Pd/CNT catalyst used in the 
hydrogenation of ethylene. The decrease in activity
 surface area which resulted in formation of larger Pd particles.
 characterize the spent Pt/CCNF catalyst (reaction temperature: 100 
the TEM image of the spent catalyst. 
Only the results for Pt/CCNF catalyst are shown in this study. In future work the Pt/CNT and 
Pt/CS will be investigated. CNTs
 Mondal et al using Pd. 
Pt represents platinum
   
5. TEM image of Pt-CeO2/CCNF 
 
 % Pt/CCNF catalyst. 
 rate of reaction at a temperature of 100 
 was due to sintering and loss of Pd 
26
  TEM analysis was used to 
oC). Figure 4.3
 It was observed that the particles have increased in size. 
27
  and CSs28 have been studied as catalyst supports by 
94 | P a g e  
 
 particles) 
oC 
nounced at high 
7 shows 
95 | P a g e  
 
0 2000 4000 6000 8000 10000
 0
 20
 40
 60
 80
 100
   30 oC
  100 oC
 Time (min)
 Co
 n
 ve
 rs
 io
 n
  
(%
 )
  
Figure 4.36. Effect of temperature on ethylene conversion over 0.5 % Pt/CCNF. [H2/C2H4 = 2; flow 
rate = 100 mL/min; catalyst mass = 0.1 g]  
  
Figure 4.37. TEM image of (a) before and (b) after hydrogenation of ethylene 
4.9.3 Effect of ceria loading 
Figure 4.38 shows the effect of different ceria loadings on the hydrogenation activity for Pt 
supported on CCNFs. An increase in ceria loading did not result in an increased rate of 
reaction. The 1 % Pt-10 % CeO2/CCNF catalyst showed ca. 70 % conversion of ethylene up 
to 3030 minutes and then the activity began to decrease. This might be due to Pt particles 
interacting with CeO2 and not the CCNFs. If the Pt nanoparticles are on the surface of ceria it 
may be easy for them to agglomerate as they are free to move. The TEM image shown in 
a b 
96 | P a g e  
 
Figure 4.39 indicates the well distributed ceria particles on the CCNFs and Pt on the surface 
of ceria. 
0 2000 4000 6000 8000 10000
 0
 20
 40
 60
 80
 100
  1% Pt-5% CeO2/CCNF
  1% Pt-10% CeO2/CCNF
 Time (min)
 Co
 n
 ve
 rs
 io
 n
  
(%
 )
  
Figure 4.38. Effect of ceria loading. .
   
[H2/C2H4 = 2; flow rate = 100 mL/min; catalyst mass = 0.1 g] 
 
Figure 4.39. TEM image of 1 % Pt-10 % CeO2/CCNF  
In conclusion, functionalization of carbon materials is an important methodology used to 
improve the anchoring of Pt nanoparticles. The polyol method was very effective in 
depositing Pt on to the support materials as the Pt nanoparticles formed were well dispersed 
with a narrow size distribution. The effects of the catalyst supports were studied using the 
hydrogenation of ethylene as a test reaction. The addition of ceria to Pt/CM catalyst proved to 
be effective in enhancing of stability and activity of the hydrogenation reaction. 
97 | P a g e  
 
References 
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1151-1162 
2. P. Serp, J. Fugueiredo, Carbon Materials for Catalysis, Wiley, USA, (2009) 132-538 
3. A.R. Harutyunyan, B.K. Pradhan, J. Chang, G. Chen, P.C. Eklund, J. Phys. Chem. B 
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4. S. Z. Mortazavi, A. J. Novinrooz, A. Reyhani, S. Mirershadi, Cent. Eur. J. Phy. 8 
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5. S. L. Knupp, W. Li, O. Paschos, T. M. Murray, J. Snyder, P. Haldar, Carbon 46 
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6. J. Wei, J. Ding, X. Zhang, D. Wu, Z. Wang, J. Luo, K. Wang, Mater. Lett. 59 (2005) 
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7. G. Leofanti, M. Padovan, G. Tozzola, B. Venturelli, Catalysis Today 41 (1998) 207-
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14. A. Plomp, T. Schubert, U. Storr, K. P. de Jong, J. H. Bitter, Top Catal. 52 (2009) 
424?430 
15. F. Rodr?guez-Reinoso, Carbon 36 (1998) 159-175 
16. Y. Zhang, Z. Wang, J. Zhou, J. Liu, K. Cen, Inte. J. Hydrogen Energy 33 ( 2008 ) 602 
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17. W. Zhang, J. Chen, G. F. Swiegers,  Z. Ma, G. G. Wallace, Nanoscale 2 (2010) 282-
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18. J. Zhao, W. Chen, Y. Zheng, Mater. Chem. Phys. 113 (2009) 591-595 
19. C. Zhang, H. He, K. Tanaka, Appl. Catal. B 65 (2006) 37?43 
20. S. H. Yang, W. H. Shin, J. W. Lee, S. Y. Kim, S. I. Woo, J. Kang, J. Phys. Chem. B 
110 (2005) 13941-13946 
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21. M. Neurock, D. Mei, Topics in Catalysis, 20 (2002) 5-23 
22. C. B. Hwang, Y. S. Fu, Y. L. Lu, S. W. Jang, P. T. Chou, C. R. Wang, S. J. Yu, J. 
Catal. 195 (2000) 336-341 
23. C. W. Chen, T. Serizawa, M. Akashi, Chem. Mater. 11 (1999) 1381-1389 
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CHAPTER FIVE 
CONCLUSIONS  
 
5.1 Introduction 
The first objective of this study was to synthesize carbon materials (CNTs, CCNFs and CSs) 
and ceria. The carbon materials (CM) were made by the chemical vapour deposition method 
(CVD) while ceria was made by the sol-gel method. The second objective was to deposit Pt 
on the carbon materials (including activated carbon (AC)), oxides (ceria and titania) and 
CeO2-CMs. The third and last objective was to test the various Pt supported catalyst for the 
hydrogenation of ethylene. The characterization techniques employed in the study included 
the use the following: TEM, TGA, BET, Raman spectroscopy, XRD, EDS, TPR, IR 
spectroscopy, UV-vis spectroscopy and ICP-AES. The study was successfully conducted and 
the following conclusions were drawn from the results. 
5.2.1 Carbon materials  
The TEM images revealed that the carbon materials were successfully produced using the 
CVD methods. For the carbon materials, acetylene was used as the carbon source and the 
catalysts employed were 5 % Fe-Co/CaCO3 (for CNT synthesis), 5 % Cu/TiO2 (for CCNF 
synthesis) and no catalyst (for the CS synthesis).  
The as-synthesized carbon materials contained some impurities. The impurities in the CCNFs 
were removed using hydrofluoric acid. The polyaromatic compounds in the carbon materials 
were removed using the Soxhlet extraction technique. Further removal of impurities was 
carried out during the functionalization of the carbon materials. Nitric acid was used to 
functionalize the carbon materials in order to introduce hydroxyl and carboxyl groups onto 
the carbon materials? surfaces. The success of the functionalization was confirmed by 
alkalimetry titration and IR spectroscopy data. 
 
 
100 | P a g e  
 
Analysis of the as-synthesized and functionalized carbon materials using Raman 
spectroscopy showed the presence of disorder in the materials whilst TGA showed the 
successful removal of impurities in the carbon materials. 
5.2.2 Ceria 
Ceria was successfully synthesized using the sol-gel method. The ceria synthesis was 
confirmed using TEM and TPR results. TEM showed the morphology of the ceria whilst TPR 
studies showed the temperature at which it reduces, which confirmed the ceria particles had 
been prepared. 
5.2.3 Titania and activated carbon 
Titania and activated carbon (AC) were obtained from Sigma-Aldrich and used without 
further purification. TEM image analysis confirmed the morphology of titania and AC. 
5.3 Deposition of platinum 
A microwave assisted polyol method was used to deposit Pt on to the various supports. The 
synthesis was successfully monitored using UV-vis spectroscopy; the disappearance of the 
peak at 260 nm in the spectrum indicated the formation of Pt nanoparticles. TEM images 
showed that the Pt nanoparticles were uniform in size and well dispersed. The presence of Pt 
and Ce were confirmed using EDS and metal loading was confirmed using ICP-AES (and 
TGA for the carbon materials). It was found that all the catalysts displayed the diffraction 
patterns of the Pt fcc structure. TPR was used to confirm that Pt was reduced fully as there 
was no peak in the profile between 177 and 302 oC, typical of Pt in a high oxidation state.  
Increasing the Pt loading on a fixed surface area of a support material resulted in an increase 
in the particle sizes. This was due to the agglomeration of the Pt nanoparticles. BET surface 
area analysis showed two trends. The first was that the BET surface area increased when Pt 
metal was loaded on the carbon materials (CCNF, CNT and CS). The second was that the 
BET surface area decreased when Pt was deposited on ceria and AC.  
 
 
 
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5.4 Hydrogenation activities of the Pt supported catalysts 
The effect of functionalization of the carbon materials was investigated and it was found that 
the functionalized carbon materials had a higher rate of reaction than the as-synthesized 
carbon materials. This was attributed to strong anchoring of Pt on the functionalized carbon 
materials. 
The hydrogenation activity increased with increased Pt metal loading. This is because when 
the loading has been increased, there are more Pt nanoparticles that are available to react with 
the reactants. The other possible reason is that the large particles produced by the high metal 
loading are less prone to sintering than the smaller particles obtained at low metal loadings. 
It was found that increasing the ratio of hydrogen to ethylene in the reactant stream resulted 
in an increase in the rate of reaction. This was attributed to the fact that at high hydrogen 
concentration, the rate of formation of carbon deposit is slow and the rate of hydrogenation is 
high. No carbon deposits are thus expected on the Pt catalyst particles. 
Titania was the best catalyst support in terms of activity results. This was attributed to the 
small particle size of platinum that was obtained on the titania surface. The small particle size 
indicates that a large fraction of active Pt atoms are on the surface and thus accessible to 
reactant molecules and available for hydrogenation reactions. Amongst the carbon materials, 
CCNF had the highest activity. This was related to the Pt particle sizes which were slightly 
smaller than found on the other carbon materials. Pt/AC had the least activity. This could be 
related to the presence of micropores, which limit the rate of diffusion of reactants to and 
from the active phase. 
The addition of ceria onto Pt/CM caused an increase in the rate of the ethylene hydrogenation 
reaction. The ethylene conversions of ceria based catalysts were higher than the Pt/CM 
catalysts. This was attributed to the role that was played by ceria of preserving the surface 
area of Pt as well as suppressing the sintering of Pt nanoparticles. However, when the CeO2 
content was too high (10 %) the hydrogenation activity decreased.  
It was found that temperature increased the rate of reaction but at high temperatures, the 
activity continually decreased. This again relates to sintering effects that are enhanced at high 
temperature. 
 
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5.5 Recommendations for future work 
Since the Pt-CeO2/CM catalyst was effective for the hydrogenation of ethylene, it will be 
good to test it for higher alkenes such as propene so that we can gain more information about 
the enhancement of catalytic activity brought about by ceria. 
Platinum is a good oxidation catalyst. It can catalyse the oxidation of CO to CO2. A high CO 
conversion occurs at high temperatures. So for the future work, it will be fascinating to work 
with Pt-CeO2/CM catalysts in the carbon monoxide oxidation reaction and establish whether 
temperature can be lowered and still maintain a high activity for oxidation reactions. 
Replacing Pt with other platinum group metals (Pd, Ru, Rh and Os) in Pt-CeO2/CM. The aim 
of the project will be to find out if ceria can maintain the enhancement of catalytic activity as 
well as to compare the different catalysts in the hydrogenation of ethylene.