i DECLARATION I declare that this thesis is my own, unaided work. It is being submitted for the degree of Doctor of Philosophy in the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other University. ??????????????.. (Signature of candidate) ??? day of ????????.2005 ii ABSTRACT The main aim of this thesis has been to study the way in which Fe(III) and Co(II) incorporation into Si-MCM-41 synthesis gels affects the properties of the unmodi- fied material. Another aim was to investigate the influence of these hetero-atoms on the dispersion and particle size distribution as well as the catalytic activity of supported Au nanoparticles in the CO oxidation reaction. Si-MCM-41 has been successfully synthesized in this work using mixtures conta- ining CTAB as a structure-directing agent (SDA) and water-glass as a SiO2 source. Replacement of water-glass with pre-calcined Si-MCM-41 for SiO2 source in the secondary synthesis step has produced Si-MCM-41 with improved structu- ral properties (XRD, HRTEM and Raman spectroscopy), including restructured and more crystalline pore walls (Raman spectroscopy). The conventional shortcomings of Si-MCM-41 as a support for catalytically- active (transition) metal components such as low hydrothermal stability, low PZC, lack of cation exchange capacity and no reducibility have been partially addressed by modification with Fe(III) and Co(II). The premodification was achieved both during framework synthesis and after synthesis by the incipient wetness impreg- nation (IWI) method. As opposed to the one-pot synthesis of metal-containing derivatives, the IWI method gave materials with high metal loadings and maximal retention of the properties of pristine Si-MCM-41. On the other hand, metal incorporation during synthesis to a loading of ~8.8 wt% using aqueous solutions of metal precursors showed some collapse of the mesostructure. Consequently methods were sought to incorporate this amount of metal (and up to double, i.e., 16 wt%) with maximal retention of the MCM-41 characteristics. These methods included (i) using Si-MCM-41 as a SiO2 source, (ii) dissolving the metal precurs- ors in an acid solution before inclusion into the synthesis gel, and (iii) using freshly precipitated alkali slurries of the metal precursors. The first method produced a highly ordered 16wt% Fe-MCM-41 material with excellent reducib- ility (TPR showed three well-resolved peaks) and pore-wall structure (Raman spe- iii ctroscopy). Like the aqueous route, the acid-mediated metal incorporation route did not produce ordered materials at metal contents of ~16 wt%. The base precipi- tate route produced highly ordered composite materials up to 16 wt% metal content, with characteristics similar to those of Si-MCM-41 (XRD, BET and HRTEM), although some metal phases were observed as a separate phase on the SiO2 surface. Thus, metal-containing MCM-41 materials could be obtained with conservation of MCM-41 mesoporosity. Raman spectroscopic studies have shown that the effect of transition metal incorporation in MCM-41-type materials is to strengthen the pore walls (shift of Si-O-Si peaks to higher frequencies), while TPR studies revealed that the essentially neutral framework of Si-MCM-41 could be rendered reducible by transition metal incorporation. Gold-containing mesoporous nanocomposites were prepared by both direct synth- esis and post-synthetically. Catalysts prepared by direct hydrothermal synthesis were always accompanied by formation of large Au particles because of the need to calcine the materials at 500 oC in order to remove the occluded surfactant template. The presence of transition metal components in Me-MCM-41 (Me = Fe and Co) has been found to play a significant role in the particle size distribution and also the dispersion of Au nanoparticles when these materials were used as supports. In general, a base metal-containing support was found to produce smaller Au nanoparticles than the corresponding siliceous support. It has been proposed that the transition metal components serve as anchoring or nucleation sites for the Au nanoparticles, which are likely to sinter during calcination. The anchoring sites thus retard the surface mobility of Au at calcination temperatures above their TTammann. The use of the Au/Me-MCM-41 materials as catalysts in the CO oxidation reaction has led to the following observations: (i) catalyst on metal-containing supports showed better activity than those on Si-MCM-41, probably due to the induced reducibility in metal-MCM-41, (ii) catalysts prepared by direct synthesis showed inferior activity owing to large Au particles, (iii) increasing Au content improves the catalytic performance, (iv) increasing the Fe content of the support iv at constant Au improves the catalytic performance, and (v) changing the base metal component of the support from Fe to Co led to a significant improvement in catalytic activity. The similarity of the apparent activation energies (Ea) for the 5 wt% Au-containing 5 wt% Fe- and 5 wt% Co-MCM-41 suggested that the difference in catalytic activity is associated with the number of active sites possessed by each catalyst system. The observed order of catalytic activity of these 5 wt% Au-containing systems in terms of the support type is: Co-MCM-41 > Fe-MCM-41 > Si-MCM-41. This was further supported by the average Au particle size, which, in terms of the support, followed the order Co-MCM-41 < Fe-MCM-41 < Si-MCM-41. Thus, metal-support interactions between Au and MCM-41 have been enhanced by introducing Fe(III) and Co(II), which also induced framework charge, ion exchange capacity (IEC) and reducibility in the neutral siliceous support. v DEDICATION This thesis is dedicated to the memory of my brother Malesela Simon Mokhonoana 1970-2003 vi ACKNOWLEDGEMENTS The extract from the late Brenda Fassie?s song, ?It?s nice to be with people? is key to success in life, because whatever we achieve in life depends on how we interact with each other. I would not have accomplished this work without the help from other people, and my sincere appreciation goes to the following people and institutions: My supervisor, Prof. N. J. Coville for his patience, guidance, support and suggestions Mr. Basil Chassoulas for his assistance with the autoclaves and TPR measurements Messrs. Barry Fairbrother and Steve Ganon for their remarkable glassblowing, fixing and making my TPR reactors. Manuel Fernandes and Prof. Schoning for their continued assistance with the XRD diffractometer, all the pains of changing receiving slits to adapt for low- angle scans. Prof. Abhaya K. Datye of the Chemical Engineering Department, University of New Mexico, Albuquerque, USA, for giving me the opportunity to research in his Group. Assistance from Hien Pham (Post-doc) and Mangesh Bore (PhD student) is also appreciated. Your guidance and suggestions are unforgettable. Prof. Harold H. Kung of the Chemical Engineering Department, Northwestern University, Evanston (Chicago), USA, for giving me a further research opportunity in his Group. Being with you was a pleasant research experience, and your approach to research will always be remembered. My parents, brothers and sisters for their support, encouragement and assistance (particularly Dr. Moses during my stay in the USA). The NRF (through the Staff Development Program) and the University of the Witwatersrand for financial support vii The NRF-NSF joint support for financing my visit and studies in the United States of America Last but not least, I would like to thank the University of the North for allowing me study leave for the period 2000-2002. viii TABLE OF CONTENTS Page DECLARATION i ABSTRACT ii DEDICATION v ACKNOWLEDGEMENTS vi TABLE OF CONTENTS viii LIST OF FIGURES xvi LIST OF TABLES xxix LIST OF ABBREVIATIONS AND ACRONYMS xxxii SCOPE AND CONTENT OF THE THESIS xxxvii APPENDICES 357 CHAPTER 1: GENERAL INTRODUCTION 1.1 Extension from Microporous to Mesoporous Dimensions 1 1.2 Synthesis and Fabrication of Mesoporous MCM-41 5 1.2.1 Liquid-Crystal Templating: Supramolecular Self-Assembly 5 1.2.2 Sol-Gel Synthesis Route (Alkali-free Synthesis) 7 1.2.3 Other Mesoporous Materials: Post-LCT Syntheses 9 1.2.3.1 Silica-Based Mesoporous Materials 9 1.2.3.2 Metal Oxide-Based Mesoporous Materials 14 1.2.3.3 Carbon-Based Mesoporous Materials 15 1.2.4 Methods of Template Removal from the Mesostructure 17 1.3 Characteristics of Mesoporous Materials (MCM-41) 18 1.3.1 Bulk and Textural features of MCM-41 18 ix 1.3.2 Morphologies and Shapes in Mesoporous MCM-41 Materials 21 1.3.3 Hydrothermal stability of MCM-41 Materials 22 1.3.3.1 Improving the thermal/hydrothermal stability of Si-MCM-41 23 1.4 Catalysis and Technical Applications of MCM-41 Materials 26 1.4.1 Organically-Modified MCM-41 Materials 26 1.4.1.1 Co-condensation or Direct Organic Modification of MCM-41 28 1.4.1.2 Post-synthesis Organic Modification of MCM-41 28 1.4.1.3 Decontamination of Ground Water: Heavy Metals and Oxyanions 29 1.4.2 Metal-containing Mesoporous Materials (Me-MCM-41) 34 1.4.2.1 Iron-containing Mesoporous MCM-41 (Fe-MCM-41) 35 1.4.2.2 Cobalt-containing Mesoporous MCM-41 (Co-MCM-41) 39 1.4.3 General Catalytic Reactions of Mesoporous Materials 45 1.5 Pollution Control Through Catalysis 46 1.5.1 Carbon Monoxide Poisoning 47 1.5.2 CO Oxidation and Catalysis by Gold 48 1.5.3 Commercial Applications of Gold Catalysts 51 1.5.4 Supported Au Catalysts 51 1.5.5 Preparation of Supported Au Catalysts 54 1.5.6 Controversy over the Active species in CO Oxidation 58 1.6 Hypotheses and Aims of the Study 59 1.7 Rationale/Motivation for Research in this Thesis 60 1.8 References 63 CHAPTER 2: MESOPOROUS SILICA MCM-41 (Si-MCM-41) 2.1 Introduction 95 x 2.1.1 Synthesis of MCM-41 96 2.2 Experimental section 99 2.2.1 Starting materials (chemicals, stock solutions and solvents) 99 2.2.2 Synthesis of the Si-MCM-41 Material (Procedure) 99 2.2.2.1 Unstirred Synthesis of Si-MCM-41 100 Room Temperature Synthesis of Si-MCM-41 100 Hydrothermal Synthesis of Si-MCM-41 100 2.2.2.2 Stirred Synthesis of Si-MCM-41 102 2.2.3 Characterization of Si-MCM-41 102 2.2.3.1 X-ray Powder Diffraction 102 2.2.3.2 BET surface area measurement 103 2.2.3.3 HRTEM studies of Si-MCM-41 103 2.3 Results and Discussion 103 2.3.1 Structural (Bulk) Characterization of Si-MCM-41 (XRD) 104 2.3.1.1 Room Temperature Synthesis 104 2.3.1.2 Hydrothermal Synthesis 113 2.3.1.3 Al-Si-MCM-41 Studies 131 2.3.2 BET surface area measurements 134 2.3.2.1 Room Temperature Synthesized Si-MCM-41 Materials 134 2.3.2.2 Hydrothermally-prepared Si-MCM-41 Materials 136 2.3.3 High Resolution Transmission Electron Microscopy (HRTEM) Studies 141 2.4 Conclusions 147 2.5 References 152 xi CHAPTER 3: IRON- AND COBALT-CONTAINING MCM-41: Synthesis and Characterization 3.1 Introduction 155 3.1.1 Probing the Fe environment in Fe-MCM-41 using ESR spectroscopy 158 3.1.2 Temperature-Programmed Reduction (TPR) 161 3.1.3 Synthetic Strategies used in this study 162 3.2 Experimental 162 3.2.1 Starting Materials 162 3.2.2 Synthesis Procedure 163 (a) Direct Synthesis: (Aqueous) Acid-mediated route 164 (b) Direct Synthesis: The hydroxide precipitate route 164 (c) Post-synthesis metal incorporation: Incipient Wetness Impregnation 164 3.2.3 Characterization of Fe- and Co-MCM-41 165 (a) X-ray Powder Diffraction (XRD) 165 (b) BET Surface Area Measurements 165 (c) High Resolution Transmission Electron Microscopy (HRTEM) 165 (d) Energy-Dispersive Spectrometry (EDS) 166 (e) Temperature-Programmed Reduction Using Hydrogen (H2-TPR) 166 (f) Electron Spin Resonance (ESR) Spectroscopy 166 (g) Raman Spectroscopy 167 (h) Infrared Spectroscopy 167 3.3 Results and Discussion 167 3.3.1 X-ray Powder Diffraction (XRD and BET) measurements 167 (a) Incipient wetness impregnation (IWI) with Fe or Co Precursors 168 (b) Direct Incorporation of aqueous Fe(III) and Co(II) During Synthesis 173 xii (c) Acid Mediated Incorporation of Fe during synthesis 178 (d) Acid-Mediated Incorporation of Co 183 (e) Simultaneous Incorporation of Fe and Co by the Acid-Mediated Route 184 (f) Base-Mediated Incorporation of Fe During Synthesis 185 1. Variation of the type of base used 185 2. Iron content 187 3. Temperature 188 (g) Base-mediated incorporation of Co 190 (h) Comparisons between Me-MCM-41 (Me = Fe, Co, Ru) prepared by the base precipitate 194 3.3.2 High Resolution Transmission Electron Microscopy (HRTEM) 196 3.3.3 Temperature-Programmed Reduction (TPR) 202 3.3.3.1 TPR studies of Fe-containing MCM-41 202 3.3.3.2 TPR studies of Co-containing MCM-41 212 3.3.3.3 TPR studies of bimetallic-derivatized MCM-41 215 3.3.4 Spectroscopic Methods 217 3.3.4.1 Electron Spin Resonance (ESR or EPR) Spectroscopy 217 3.3.4.2 Raman Spectroscopy 225 3.3.4.3 Infrared Spectroscopy 233 3.4 Conclusions 235 3.5 References 240 CHAPTER 4 SYNTHESIS AND CHARACTERIZATION OF Au- CONTAINING Me-MCM-41 (Me = Si, Co, Fe) 4.1 Introduction 247 4.1.1 Synthesis of Supported Gold Nanoparticles: General 249 xiii 4.1.2 Gold Nanoparticles on Haruta-type Supports 249 (i) Coprecipitation (CP) 251 (ii) Deposition-precipitation (DP) 252 4.1.3 Gold Nanoparticles on Conventional Zeolite Supports 252 4.1.4 Gold Nanoparticles on Mesoporous Zeolite Supports 253 4.1.5 Characterization of Supported Gold Nanoparticles 254 4.1.6 Aim of Study 256 4.2 Experimental 257 4.2.1 Materials 257 4.2.2 Synthesis of Mesostructured Au/Me-MCM-41 (Me = Si, Co, Fe) 257 4.2.2.1 One-pot Synthesis of Au-containing MCM-41: Direct 80-100 oC Synthesis 258 4.2.2.2 Post-synthesis Approach to Au-containing MCM-41: Ethylenediamine route 258 4.2.2.3 Post-synthesis Approach to Au-containing MCM-41: Coprecipitation route 259 4.2.2.4 Post-synthesi Approach to Au-containing MCM-41: Miscellaneous 259 4.2.3 Characterization of Au/Me-MCM-41 (Me = Si, Fe, Co) 259 4.3 Results and Discussion 260 4.3.1 X-ray Diffraction Studies 260 4.3.2 BET Surface Area Measurements 264 4.3.3 High Resolution Transmission Electron Microscopy (HRTEM) Studies 267 4.3.3.1 Gold Incorporation by Direct Hydrothermal Synthesis (One-pot Synthesis) 267 4.3.3.2 Post-synthesis incorporation of Au in Mesoporous Supports 270 xiv 4.3.3.3 Gold Incorporation by Precipitation with ethylenediamine solution and calcinations 270 4.3.3.4 Gold Incorporation by other Methods (Post-synthetically) 280 4.4 Conclusions 287 4.5 References 291 CHAPTER 5: CO OXIDATION OVER Au/Me-MCM-41 (Me = Si, Fe, Co) MATERIALS 5.1 Introduction 298 5.1.1 Gold Catalysts Supported on Mesoporous Silica Derivatives 302 5.2 Experimental 304 5.2.1 Starting Materials 304 5.2.2 Catalyst Preparations 305 Method A 305 Method B 305 Method C 306 5.2.3 Activity Testing Procedure 306 5.3 Results and Discussion 308 5.3.1 Gold Catalysts on Pure Silica MCM-41 Supports 308 5.3.2 Gold Catalysts on Co-functionalized Mesoporous Supports 312 5.3.3 Gold Catalysts on Fe-functionalized Mesoporous Supports 315 5.3.4 Gold catalysts on Fe-functionalized MCM-41: Ethylenediamine Synthesis route 317 5.3.5 Gold catalysts on Fe-functionalized MCM-41: Other Post-synthesis Methods 327 5.4 Conclusions 334 5.5 References 339 xv CHAPTER 6 SUMMARY AND CONCLUSIONS 6.1 Summary 343 6.2 Conclusions 345 APPENDICES Appendix A.1. The XRD patterns of Si-MCM-41 materials prepared at 80 oC for 6 h under magnetic stirring. The ratio RSiO2 represents molSiO2(TEOS) divided by molSiO2(water-glass) in the synthesis gel. 357 Appendix A.2. Table of lattice parameters of Si-MCM-41 (prepared at 100 oC for 2 days) as a function of the synthesis gel H2O content 358 Appendix A.3. XRD pattern of 20 wt% Fe-MCM-41 prepared at 100 oC for 2 days via the OH- precipitate route 359 Appendix A.4. XRD patterns of 16 wt% Fe-MCM-41 (100 oC, 2 d) using different precipitants (TEA and Na2CO3). 360 Appendix A.5 (i). The EDS spectrum of 5 wt% Au/14 wt% Fe-MCM-41 prepared via the (en) route on the Fe-rich support, followed by calcination at 380 oC for 6 h. Average particle size 3.55 nm. 361 Appendix A.5 (ii). EDS spectrum of 2.28 wt% Au/CTAB-MCM-41 prepared via the en route, and then calcined at 500 oC for 12 h to decompose the surfactant. Note that the Au content is relative to the as-synthesized material, and the actual Au content is actually higher than the stipulated value 361 Appendix A.6 Raw data for the CO oxidation reaction using 1.48 wt% Au.Co- MCM-41 as a catalyst, calcined at 325 oC for 6 h 362 Appendix A.7. The framework Raman spectrum of sec-Si-MCM-41 prepared at 100 oC for 48 h and then calcined at 560 oC for 6 h 363 Appendix A.8. Conferences Attended and Presentations 364 xvi LIST OF FIGURES CHAPTER 1 Figure 1.1 Three structure types observed for silica-surfactant mesophases: (a) MCM-41 (Hexagonal, 1-D), (b) MCM-48 (Cubic, bicontinuous, 3-D), (c) MCM- 50 (Lamellar, 2-D) 4 Figure 1.2 Liquid-crystal templating (LCT) mechanism for self-assembly proposed by Beck et al [26] showing two possible pathways for the formation of MCM-41: (1) liquid-crystal initiated and (2) silicate-initiated 6 Figure 1.3 SEM micrograph of SBA-2 showing different morphologies 12 Figure 1.4 (Left) Changes in powder XRD patterns during synthesis of the carbon molecular sieve CMK-1 with its silica template MCM-48: (a) The mesoporous silica molecular sieve MCM-48, (b) MCM-48 after completing carbonization within pores, and (c) CMK-1. (Right): Powder XRD patterns of CMK-3 carbon and SBA-15 silica used as template for the CMK-3 synthesis 16 Figure 1.5 TEM images of MCM-41 materials with Ar pore sizes of (a) 20, (b) 40, (c) 65 and (d) 100 ? 19 Figure 1.6 XRD pattern (a) of high-quality calcined MCM-41 reported by Huo et al [34], and N2 adsorption isotherm (b) reported by Branton et al [127] 20 Figure 1.7 SEM images of (a) BMS-1, (b) BMS-2, and (c) BMS-3. The length of the bar for (a, b) corresponds to 5 ?m and for (c) corresponds to 10 ?m. Varying amounts of ethyl acetate were added to the synthesis mixture for the preparation of the BMS materials, with BMS-1, BMS-2 and BMS-3 prepared by adding 15, 25 and 35 ml, respectively, of ethyl acetate to the synthesis gel [ref. 144] 21 Figure 1.8 Powder XRD patterns of Si-MCM-41 and Si-Al-MCM-41 (a) before and (b) after treatment in boiling water for 1 week 25 Figure 1.9 SBET of Si-MCM-41, Si-Al-MCM-41, and Al/Si-MCM-41 before and after treatment in boiling water for 1 week: ? fresh sample, ? in boiling water. The last material was prepared by Al impregnation of Si-MCM-41 25 Figure 1.10 Recipe for the formation of a silica sponge (A), and retention of the hexagonal structure (B) 31 Figure 1.11 Heavy metal removal by SAMMS 32 Figure 1.12 XRD patterns of Co/MCM-41 and MCM-41 40 Figure 1.13 Zeta potential of MCM-41 as a function of pH. The dotted line indicates the isoelectric point 42 xvii Figure 1.14 TPR patterns of CoMo/Al-MCM(x) catalysts, x is the weight % of MCM-41 in the support 43 Figure 1.15 TEM micrograph of Au-Fe (1 : 19) coprecipitate calcined at 400 oC: dispersion of gold over ?-Fe2O3 52 Figure 1.16 Conversions of H2 and CO in catalytic oxidation reactions as a function of catalyst temperature. CO or H2 1 vol% in air, SV = 2 ? 104 h-1.ml/g- cat: oxidation of H2 (?) and CO (?) on Au-Fe (1 : 19) coprecipitate calcined at 400 oC in air; oxidation of H2 (?) and CO (?) on Au powder prepared from colloidal metal particles with diameters around 20 nm; oxidation of H2 (?) and CO (?) on ?-Fe2O3 powder prepared by calcination of ferric hydroxide at 400 oC 53 Figure 1.17 Arrhenius plots for the rate of CO oxidation over supported catalysts: (?) Au (1.2 wt%)/Co3O4, (?) Au (0.66 wt%)/?-Fe2O3 and (?) Au (3.3 wt%)/TiO2 53 CHAPTER 2 Figure 2.1 XRD patterns of Si-MCM-41 samples: Different batches prepared on different days using gels of the same composition (mean ao = 46.7 ?) 101 Figure 2.2 XRD patterns of Si-MCM-41 materials synthesized at room tempera- ture for 47 days. Replicate syntheses were done using distilled water and deioni- zed water as solvent media 105 Figure 2.3 XRD patterns of some Si-MCM-41 materials prepared at room temperature 106 Figure 2.4 XRD patterns of Si-MCM-41 made at RT using templates of different alkyl chain lengths: aC14 represents tetradecyltrimethylammonium bromide, and C16 represents cetyltrimethylammonium bromide (a.k.a. CTAB) 108 Figure 2.5 The XRD patterns of Si-MCM-41 prepared at RT from gels of varying silicon/surfactant ratios 110 Figure 2.6 Variation of the lattice parameter with synthesis gel H2O content (RT, 5 days) 111 Figure 2.7 XRD patterns of secondary Si-MCM-41: (a) primary Si-MCM-41 (parent), and (b) 2o synthesis at RT for 2 days 112 Figure 2.8 XRD pattern of Si-MCM-41 prepared by aging at RT for 5 days, with water-glass first titrated with HNO3 prior adding to CTAB solution. Calcined at 560 oC for 6 h 113 xviii Figure 2.9 XRD patterns of Si-MCM-41 showing the effect of synthesis temperature (3 days synthesis) 114 Figure 2.10 A plot of ao versus synthesis temperature for Si-MCM-41, 3 days synthesis. Room temperature has been arbitrarily taken as 25 oC. 115 Figure 2.11 XRD patterns of Si-MCM-41 made from gels with different pH values (2 days) 116 Figure 2.12 The XRD pattern of Si-MCM-41 prepared by intermediate pH adjustment 117 Figure 2.13 XRD patterns of calcined Si-MCM-41 prepared at 100 oC for 12-72 h: (a) 1o ? 2? ? 10o, and (b) 3o ? 2? ? 10o (higher order region) 118 Figure 2.14 Variation of ao with synthesis time at 100 oC for Si-MCM-41 119 Figure 2.15 XRD patterns of Si-MCM-41, RT v/s 100 oC synthesis: (a) 3 days, (b) 5 days 120 Figure 2.16 A plot of lattice parameter versus gel H2O/SiO2 molar ratio (Si- MCM-41, 100 oC, 2 days) 121 Figure 2.17 XRD patterns of Si-MCM-41 prepared in a pH 10 buffer solution 121 Figure 2.18 XRD pattern of Si-MCM-41 prepared by doubling the gel composition 123 Figure 2.19 XRD patterns of Si-MCM-41 prepared using different acids 124 Figure 2.20 XRD patterns of Si-MCM-41 synthesized at 100 oC for 2 days 125 Figure 2.21 XRD patterns of Si-MCM-41, showing the effect of the silica precursor 126 Figure 2.22 XRD patterns of secondary Si-MCM-41: Effect of calcination temperature 127 Figure 2.23 The XRD patterns of secondary Si-MCM-41: Effect of synthesis time, (a) full range, and (b) 3o ? 2? ? 10o 129 Figure 2.24 XRD pattern of Si-MCM-41 prepared by heating the synthesis gel (97 oC for 45 minutes) made with pre-hydrolysis of water-glass with HNO3 before adding to CTAB solution. Calcined at 560 oC for 6 h 130 xix Figure 2.25 XRD patterns of (Al, Si)-MCM-41 (Si/Al = 30) prepared at 100 oC for 48 h: (a) Al source added to the gel after pH adjustment, (b) Al source added to the gel before pH adjustment, followed by 2 days aging prior to synthesis, and (c) Al source added to the gel before pH adjustment 132 Figure 2.26 XRD patterns of (Al, Si)-MCM-41 (Si/Al = 22) prepared by IWI of Si-MCM-41. (a) methanol as solvent, (b) water as solvent, and (c) ethanol as solvent. IWI abbreviates incipient wetness impregnation 133 Figure 2.27 XRD patterns of (Al, Si)-MCM-41 (Si/Al = 22) by different synthesis routes 134 Figure 2.28 Variation of the BET surface area of Si-MCM-41 with gel water content (RT, 5 days) 135 Figure 2.29 Variation of the BET surface area with synthesis time for Si-MCM- 41 (100 oC) 137 Figure 2.30 HRTEM images of Si-MCM-41 prepared at 100 oC for 5 days, and calcined at 560 oC for 6 h 142 Figure 2.31 HRTEM images of Si-MCM-41 made with CTAB/NaK-tartrate as template, calcined at 560 oC for 6 h: Images taken at different regions of the same sample 143 Figure 2.32 Different regions of Si-MCM-41 (2 days, 100 oC, C14TMAB as template, calcined at 560 oC for 6 h) as seen under HRTEM 144 Figure 2.33 HRTEM images of different regions of Si-MCM-41 prepared at 80 oC for 6 h, RSiO2 = 3.95, and calcined at 500 oC for 12 h 145 Figure 2.34 HRTEM images of different regions of Si-MCM-41 prepared at 80 oC for 6 h, with RSiO2 = 1.48, and calcined at 500 oC for 12 h 146 CHAPTER 3 Figure 3.1 TEM micrograph of 4 wt% Fe-MCM-41. Fe introduced during framework synthesis 157 Figure 3.2 Room temperature X-band EPR spectrum of the iron-containing Kenyaite 160 Figure 3.3 XRD patterns of 5 wt% Fe-MCM-41 (a) and the pure support (b) 168 Figure 3.4 The XRD pattern of 5 wt% Fe-MCM-41 prepared by IWI of sec-Si- MCM-41, calcined at 560 oC for 6 h. Insert: Expanded high-angle region, * represents Fe2O3 169 xx Figure 3.5 XRD patterns of Fe-MCM-41 prepared by IWI compared with that of bulk Fe2O3: (a) 16 wt% Fe-MCM-41, (b) 50 wt% Fe-MCM-41, and (c) bulk Fe2O3 171 Figure 3.6 XRD patterns of 16 wt% Co-MCM-41 prepared by IWI in 1 M HNO3 solution (a) and Co3O4 reference sample (b) 172 Figure 3.7 Effect of Co incorporation by IWI on XRD patterns: (a) parent Si- MCM-41 and (b) 10.2 wt% Co-MCM-41 172 Figure 3.8 Effect of synthesis gel pH on the XRD properties of hydrothermally- prepared 1.9 wt% Fe-MCM-41 173 Figure 3.9 XRD patterns of 8.8 wt% Fe-MCM-41: Solid NaOH versus aqueous NaOH for pH adjustment 174 Figure 3.10 XRD pattern of 8.9 wt% Co-MCM-41 prepared at 100 oC for 72 h (one-pot synthesis) 175 Figure 3.11 Low-angle (a) and high-angle (b) XRD patterns of 16 wt% Fe-MCM- 41: Fe3+(aq) added after 2 h stirring. Synthesis at 100 oC for 6 h, dried at 110 oC for 3 h, uncalcined 176 Figure 3.12 Variation of ao with calcination temperature for 5 wt% Fe-MCM-41 prepared at 100 oC for 2 days 178 Figure 3.13 XRD patterns of 5 wt% Fe-MCM-41 calcined at different tempera- tures 179 Figure 3.14 Lattice parameters for 8.8 wt% Fe-MCM-41 prepared at 100 oC for 2 days using various acids to add the Fe precursor 180 Figure 3.15 Variation of BET surface areas of 8.8 wt% Fe-MCM-41, prepared at 100 oC for 2 days, with acid identity. All samples were calcined at 560 oC for 6 h 181 Figure 3.16 Variation of the BET surface area (a) and lattice parameter (b) with Fe content for the Fe-MCM-41 materials prepared in HNO3 at 100 oC for 48 h. All samples were calcined at 560 oC for 6 h 182 Figure 3.17 XRD patterns of a bimetallic and monometallic Fe-MCM-41 prepared at 100 oC for 2 days with metal precursors in 1 M HNO3: (a) 8.8 wt% Fe-MCM-41 and (b) (7.8 wt% Fe, 11.5 wt% Co)-MCM-41 184 Figure 3.18 XRD patterns of Fe-MCM-41 prepared via the OH- route and calcined at 560 oC for 6 h: (a) 5 wt% Fe-MCM-41, (b) 10 wt% Fe-MCM-41, (c) 16 wt% Fe-MCM-41, and (d) bulk Fe2O3 187 xxi Figure 3.19 The XRD patterns of 5 wt% Fe-MCM-41 prepared by adding Fe(OH)3 to the synthesis gel and carrying out the synthesis (a) at 97 oC for 45 minutes and (b) at room temperature for 4 days 189 Figure 3.20 XRD patterns of Co-MCM-41 prepared by the OH- route at 100 oC for 48 h and calcined at 560 oC for 6 h 191 Figure 3.21 XRD patterns of 10 wt% Co-MCM-41 prepared hydrothermally via the hydroxide route: (a) calcined at 560 oC for 6 h, and (b) after the TPR experiment 192 Figure 3.22 XRD pattern of 16 wt% Co-MCM-41 (5 days at RT, OH- route) 192 Figure 3.23 High-angle XRD patterns of Co3O4 (a), 16 wt% Co-MCM-41 prepared at RT for 5 days (b), and 16 wt% Co-MCM-41 prepared at 100 oC for 2 days (c) 193 Figure 3.24 XRD patterns of 16 wt% Me-MCM-41 prepared via the NaOH precipitate route: Me = Co (a), Fe (b) and Ru (c). All materials calcined at 560 oC for 6 h 194 Figure 3.25 HRTEM micrograph (a) and EDS (b) of 16 wt% Fe-MCM-41 prepared by IWI method. After overnight drying at 110 oC, the sample was calcined at 560 oC for 6 h 197 Figure 3.26 HRTEM micrograph of 5 wt% Fe-MCM-41 prepared by IWI on sec- Si-MCM-41 198 Figure 3.27 HRTEM micrograph (a) and EDS (b) of 14 wt% Fe-MCM-41 material made from TEOS and urea at 80-90 oC for 24 h 199 Figure 3.28 HRTEM micrograph of 7.5 wt% Fe-silica material made by the aerosol route at 125 oC 200 Figure 3.29 HRTEM micrograph of 3 wt% Fe-MCM-41 prepared at 80 oC for 6 h. The material was then calcined at 500 oC for 12 h 200 Figure 3.30 HRTEM micrographs of two different regions of 5 wt% Fe-MCM-51 prepared via the OH- route at 100 oC for 2 days 201 Figure 3.31 TPR profiles of 16 wt% Fe-MCM-41 prepared by IWI: (a) calcined at 450 oC for 12 h, (b) calcined at 560 oC for 6 h, and (c) bulk Fe2O3 reference 202 Figure 3.32 TPR profiles of (a) 5 wt% Fe-MCM-41 prepared by IWI method using sec-Si-MCM-41 as a support, calcined at 560 oC for 6 h, (b) bulk Fe2O3 203 xxii Figure 3.33 TPR profiles of (a) 16 wt% Fe-MCM-41 prepared by adding Fe3+(aq) to the synthesis gel 2 h after mixing (but prior to hydrothermal synthesis and calcination at 560 oC for 6 h)), and (b) bulk Fe2O3 204 Figure 3.34 TPR profiles of (a) 16 wt% Fe-MCM-41 prepared hydrothermally from Fe3+(aq) and Si-MCM-41 as a SiO2 source followed by calcination at 560 oC for 6 h, (b) bulk Fe2O3 205 Figure 3.35 TPR profile of (a) Fe2O3 and (b) 8.8 wt% Fe-MCM-41 prepared by HNO3-mediated incorporation of Fe(III) (2 days at 100 oC) and calcined at 560 oC for 6 h 206 Figure 3.36 TPR profiles of Fe-MCM-41 prepared via NaOH precipitate (100 oC for 2 days): (a) 5 wt% Fe, (b) 10 wt% Fe, and (c) bulk Fe2O3 207 Figure 3.37 TPR profiles of 16 wt% Fe-MCM-41 prepared via the OH- route at 100 oC for 5 days: (a) calcined at 450 oC for 12 h, and (b) calcined at 560 oC for 6 h 208 Figure 3.38 The TPR profiles of (a) 16 wt% Fe-MCM-41 prepared by delayed addition of Fe(OH)3 to the synthesis gel (100 oC for 2 days) and (b) bulk Fe2O3 209 Figure 3.39 TPR profiles of 16 wt% Fe-MCM-41 prepared at 100 oC for 2 days via the OH- precipitate route: (a) Na2CO3 and (b) (HOCH2CH2)3N as precipitants 210 Figure 3.40 TPR profiles of (a) 5 wt% Fe-MCM-41 prepared via NaOH precipitation of Fe3+ at RT for 4 days and (b) bulk Fe2O3 211 Figure 3.41 TPR profiles of Co3O4: (a) synthesized in this work, (b) reported by Wu et al 212 Figure 3.42 TPR profiles of (a) 16 wt% Co-MCM-41 prepared by IWI with a 1 M HNO3 solution of Fe3+ and calcined at 560 oC for 6 h, and (b) bulk Co3O4 213 Figure 3.43 TPR profiles of Co-MCM-41 prepared via OH- precipitates at 100 oC for 2 days: (a) 5 wt% Co, (b) 10 wt% Co, and (c) bulk Co3O4. All Co-MCM-41 were calcined at 560 oC for 6 h 214 Figure 3.44 TPR profiles of 10 wt% Co-MCM-41 prepared via the OH- route at 100 oC for 2 days: (a) calcined at 560 oC for 6 h, (b) calcined at 450 oC for 12 h and (c) bulk Co3O4 215 Figure 3.45 TPR profiles of (a) Fe2O3 and (b) (7.8 wt% Fe, 11.5 wt% Co)-MCM- 41 prepared at 100 oC for 2 days using a HNO3 solution of the metal precursors, and calcined at 560 oC for 6 h 216 xxiii Figure 3.46 TPR profile of (1.9 wt% Au, 6.5 wt% Fe)-MCM-41 prepared by coprecipitation of Au(III) and Fe(III) with water-glass prior to hydrothermal synthesis at 100 oC for 5 days, calcined at 560 oC for 6 h 217 Figure 3.47 Room temperature X-band ESR spectra of 5 wt% Fe-MCM-41 prepared at 100 oC for 2 days, as a function of calcination temperature: (a) as- synthesized, (b) 300 oC for 6 h, (c) 400 oC for 6 h, and (d) 560 oC for 6 h 218 Figure 3.48 ESR spectrum of as-synthesized 8.8 wt% Fe-MCM-41 prepared by room temperature synthesis for 5 days with a HNO3 solution of Fe(III) 219 Figure 3.49 ESR spectrum of 8.8 wt% Fe-MCM-41 prepared at 100 oC for 2 days using Fe(III) in maleic acid solution, followed by calcination at 560 oC for 6 h 220 Figure 3.50 ESR spectrum of calcined (560 oC for 6 h) 8.8 wt% Fe-MCM-41 prepared at RT for 5 days with Fe(III) in oxalic acid solution 221 Figure 3.51 The ESR spectrum of 16 wt% Fe-MCM-41 prepared by IWI with a 1 M HNO3 solution of Fe(III), and calcined at 560 oC for 6 h 222 Figure 3.52 ESR spectrum of 16 wt% Ru-MCM-41 prepared at 100 oC for 2 days using the OH- synthesis route, and calcined at 560 oC for 6 h 222 Figure 3.53 ESR spectra of 16 wt% Co-MCM-41 prepared by IWI with HNO3 solution of Co(II): (a) dried overnight at 110 oC, and (b) calcined at 560 oC for 6 h 224 Figure 3.54 ESR spectra of 16 wt% Co-MCM-41 prepared by one-pot synthesis via the OH- route under different conditions: (a) 100 oC for 48 h, calcined at 560 oC for 6 h, (b) RT synthesis for 5 days, uncalcined 224 Figure 3.55 Raman spectra of Si-MCM-41 in the framework region: (a) primary Si-MCM-41 and (b) sec-Si-MCM-41 (prepared using calcined Si-MCM-41 as a SiO2 source) 225 Figure 3.56 Raman spectra of Si-MCM-41 showing the OH stretching region: (a) primary Si-MCM-41 and (b) secondary Si-MCM-41 226 Figure 3.57 Framework Raman spectra or 5 wt% Fe-MCM-41 (2 days at 100 oC): (a) as-synthesized, (b) calcined at 300 oC for 6 h, (c) calcined at 400 oC for 6 h, and (d) calcined at 560 oC for 6 h 227 Figure 3.58 Raman spectra of 5 wt% Fe-MCM-41 (2 days at 100 oC) in the OH region: (a) as-synthesized, (b) calcined at 400 oC for 6 h, and (c) calcined at 560 oC for 6 h 228 xxiv Figure 3.59 Variation of the Raman OH band (3476 cm-1) area of Fe-MCM-41 prepared at 100 oC for 2 days using HNO3 for iron incorporation. All samples were calcined at 560 oC for 6 h 229 Figure 3.60 Framework Raman spectra of 16 wt% Fe-MCM-41 prepared with Si- MCM-41 as a SiO2 source (100 oC for 2 days) and calcined at 560 oC: (a) sec-Si- MCM-41 reference sample, (b) calcined for 3 h, and (c) calcined for 6 h 230 Figure 3.61 Raman spectra of 16 wt% Fe-MCM-41 prepared by the TMAOH precipitate route: (a) as-synthesized, (b) calcined at 560 oC for 6 h 231 Figure 3.62 Comparative Raman spectra of 16 wt% Co-MCM-41 prepared by IWI from nitric acid solution, and hydrothermally via the Co(OH)2 route: (a) Frame-work region and (b) OH region. All samples were calcined at 560 oC for 6 h 232 Figure 3.63 IR spectra (KBr pellet) fo Fe-MCM-41 prepared at 100 oC for 48 h using HNO3-assisted incorporation of Fe(III): (a) Si-MCM-41, (b) 1.9 wt% Fe- MCM-41, (c) 5.5 wt% Fe-MCM-41, and (d) 8.8 wt% Fe-MCM-41. All materials calcined at 560 oC for 6 h 233 CHAPTER 4 Figure 4.1 Variation of CO oxidation activity as a function of Au cluster size for the model Au/TiO2 (001)/Mo(100) system 248 Figure 4.2 XRD patterns of 1.92 wt% Au/6.5 wt% Fe-MCM-41 prepared by direct hydrothermal synthesis at 100 oC for 5 days, from a water-glass coprecipitate of the metal precursors 261 Figure 4.3 XRD pattern of 3 wt% Au/5 wt% Fe/MCM-41 prepared by coprecipi- tating Au(III) and Fe(III) with a Na2CO3 solution in the presence of calcined Si- MCM-41 that was synthesized at 120 oC for 3 days. The material was oven-dried at 120 oC for 15 minutes prior to XRD analysis 262 Figure 4.4 XRD patterns of 1.6 wt% Au/0.73 wt% Fe/MCM-41 (a) and 1.5 wt% Au/5 wt% Fe/MCM-41 (b) prepared by coprecipitating Au(III) and Fe(III) with Na2CO3 (aq) in the presence of calcined Si-MCM-41 that was synthesized at 120 oC for 3 days. Both materials were air-dried before XRD measurements 263 Figure 4.5 XRD pattern of 1.5 wt% Au/5 wt% Co/MCM-41 prepared by copreci- pitating Au(III) and Co(II) with Na2CO3 (aq) in the presence of preformed Si- MCM-41 that was synthesized at 120 oC for 3 days 264 Figure 4.6 HRTEM micrograph (a) and PSD (b) of 1.285 wt% Au/MCM-41 prepared by direct synthesis at 96 oC for 3 h. The synthesis gel was initially aged at room temperature in a PP bottle before carrying out the hydrothermal synthesis, and the final material was calcined at 500 oC for 12 h 268 xxv Figure 4.7 HRTEM image (a) and particle size distribution (b) of 2.6 wt% Au/2.96 wt% Fe-MCM-41 prepared in situ at 80 oC for 6 h and calcined at 500 oC for 12 h 269 Figure 4.8 HRTEM image (a) and PSD (b) of 5 wt% Au/Si-MCM-41 prepared by precipitating Au(III) with (en) in the presence of calcined Si-MCM-41, calcined at 400 oC for 4 h 270 Figure 4.9 HRTEM image (a) and PSD (b) of 1 wt% Au/3 wt% Fe-MCM-41 prepared by precipitating Au(III) with en solution in the presence of calcined 3 wt% Fe-MCM-41, calcined at 400 oC for 4 h 272 Figure 4.10 HRTEM image (a) and PSD (b) of 2.57 wt% Au/3 wt% Fe-MCM-41 prepared by precipitating Au(III) with en solution in the presence of calcined 3 wt% Fe-MCM-41, calcined at 400 oC for 4 h 273 Figure 4.11 HRTEM image (a) and PSD (b) of 5 wt% Au/3 wt% Fe-MCM-41 prepared by precipitating Au(III) with en solution in the presence of calcined 3 wt% Fe-MCM-41, calcined at 400 oC for 4 h 274 Figure 4.12 HRTEM image (a) and PSD (b) of 5wt% Au/5 wt% Fe-MCM-41 prepared by precipitating Au(III) with en solution in the presence of calcined 5 wt% Fe-MCM-41, followed by calcination at 400 oC for 4 h 275 Figure 4.13 HRTEM image (a) and PSD (b) of 5 wt% Au/5 wt% Fe-MCM-41 prepared by precipitating Au(III) with en solution in the presence of preformed 5 wt% Fe-MCM-41, then treated to incipient wetness with a dilute base solution (0.27 % NaBH4/0.89 % NaOH/8.85 % H2O) prior to calcination at 400 oC for 4 h 276 Figure 4.14 HRTEM image (a) and PSD (b) of 5 wt% Au/14 wt% Fe-MCM-41 prepared by precipitating Au(III) with en in the presence of calcined 14 wt% Fe- MCM-41, followed by calcination at 380 oC for 6 h 277 Figure 4.15 HRTEM image (a) and PSD (b) of 1 wt% Au/5 wt% Co-MCM-41 prepared by precipitating Au(III) with en in the presence of 5 wt% Co-MCM-41, followed by calcination at 400 oC for 4 h 278 Figure 4.16 HRTEM image (a) and PSD (b) of 5 wt% Au/5 wt% Co-MCM-41 prepared by precipitating Au(III) with en in the presence of preformed 5 wt% Co- MCM-41, calcined at 400 oC for 4 h 279 Figure 4.17 The HRTEM image of 2.28 wt% Au/CTAB-Si-MCM-41 prepared by ethylenediamine precipitation of Au(III). The material is in its uncalcined state 280 xxvi Figure 4.18 HRTEM image (a) and PSD (b) of 2.28 wt% Au/CTAB-Si-MCM-41 prepared by precipitating Au(III) with en in the presence of the as-synthesized Si- MCM-41, followed by calcination at 500 oC for 12 h 281 Figure 4.19 HRTEM image (a) and PSD (b) of 2.67 wt% Au/3 wt% Fe-MCM-41 prepared by precipitating Au(III) with urea in the presence of 3 wt% Fe-MCM-41, calcined at 400 oC for 4 h 283 Figure 4.20 HRTEM image (a) and PSD (b) of 1.1 wt% Au/3 wt% Fe-MCM-41 prepared by reducing Au(III) with sodium citrate in the presence of calcined 3 wt% Fe-MCM-41, calcined at 325 oC for 6 h 284 CHAPTER 5 Figure 5.1 CO conversion as a function of temperature for different supported Au catalysts: Au on wormhole mesoporous silica, Au on hexagonally ordered mesoporous silica, Au on mesoporous titania calcined at 150 oC, and Au on mesoporous titania calcined at 200 oC 304 Figure 5.2 The catalyst testing set-up for the CO oxidation reaction 307 Figure 5.3 Light-off curve for 1.285 wt% Au/Si-MCM-41 prepared by prior aging the synthesis gel at room temperature for 20 h, followed by treatment at 96 oC for 6 h and 500 oC calcination at 500 oC for 12 h 309 Figure 5.4 Light-off curve for 2.28 wt% Au/Si-MCM-41 prepared from AuCl4- and as-synthesized Si-MCM-41 via the (en) route. Material calcined at 500 oC for 12 h 310 Figure 5.5 Light-off curve for 5 wt% Au/Si-MCM-41 prepared by (en) deposition-precipitation of AuCl4- onto precalcined Si-MCM-41. The catalyst system was then calcined at 400 oC for 4 h 311 Figure 5.6 The light-off curves of Au/5 wt% Co-MCM-41 prepared by DP with (en) solution and calcination at 400 oC for 4 h: The effect of Au content 313 Figure 5.7 The light-off curves of 1.48 wt% Au/5 wt% Co-MCM-41 prepared via the (en) deposition route and subjected to two different calcination processes. Neither HRTEM nor BET analysis was done on these samples and therefore, no average Au particle diameter has been determined 314 Figure 5.8 The light-off curves for Au/3 wt% Fe-MCM-41 prepared by direct hydrothermal synthesis at 80 ? 2 oC for 6 h, followed by calcination at 500 oC for 12 h: The effect of Au content 315 Figure 5.9 TOS curve for CO oxidation using 5 wt% Au/3 wt% Fe-MCM-41 prepared by hydrothermal synthesis at 80 ? 2 oC for 6 h, followed by calcination at 500 oC for 12 h. Measurements were performed at 22 oC 316 xxvii Figure 5.10 The light-off curves for Au/3 wt% Fe-MCM-41 prepared by (en) deposition of Au(III) onto 3 wt% Fe-MCM-41, showing the effect of Au content. All samples were calcined at 400 oC for 4 h 317 Figure 5.11 Light-off curves for 5 wt% Au-containing materials prepared by the (en) route, showing the effect of the amount of Fe in the support. All materials were calcined at 400 oC for 4 h 319 Figure 5.12 Light-off curves for differently treated 5 wt% Au/5 wt% Fe-MCM-41 materials prepared via the (en) route: Effect of NaBH4 treatment prior calcination at 400 oC for 4 h 321 Figure 5.13 CO conversion versus time on stream for 5 wt% Au/5 wt% Fe-MCM- 41 prepared by ethylenediamine deposition of Au(III) onto preformed 5 wt% Fe- MCM-41, treated with NaBH4 and then calcined at 400 oC for 4 h 322 Figure 5.14 The light-off curve for 10 wt% Au/5 wt% Fe-MCM-41 prepared by ethylenediamine deposition onto preformed 5 wt% Fe-MCM-41, calcined at 325 oC for 6 h 323 Figure 5.15 The light-off curve for 5 wt% Au/14 wt% Fe-MCM-41 prepared via ethylenediamine deposition of Au(III) onto preformed 14 wt% Fe-MCM-41, calcined at 350 oC for 6 h 324 Figure 5.16 Effect of metal identity on the light-off temperatures of 5 wt% Au catalysts prepared by ethylenediamine deposition of Au(III) on various supports. All materials calcined at 400 oC for 4 h 325 Figure 5.17 The Arrhenius plots for the CO oxidation reaction using 5 wt% Au catalysts supported on Si-MCM-41, 5 wt% Fe-MCM-41 and 5 wt% Co-MCM-41. The materials were prepared via the ethylenediamine deposition route and calcin- ed at 400 oC for 4 h 326 Figure 5.18 Light-off curves for the Au-containing materials prepared by urea deposition-precipitation of Au(III) onto preformed 3 wt% Fe-MCM-41, calcined at 400 oC for 4 h 328 Figure 5.19 Light-off curves for Au/5 wt% Fe-MCM-41 materials prepared by CP of Au(III) and Fe(III) with NaOH at 90 oC, calcined at 400 oC for 4 h 329 Figure 5.20 Light-off curve for 1.07 wt% Au/3 wt% Fe-MCM-41 prepared by sodium citrate reduction at 80 oC, calcined at 325 oC for 6 h 330 Figure 5.21 Light-off curves for uncalcined Au-containing materials prepared by coprecipitation in the presence of Si-MCM-41, showing the effect of Au loading 331 xxviii Figure 5.22 Light-off curves for uncalcined Au-containing materials prepared by coprecipitation of Au(III) and Fe(III) in the presence of preformed Si-MCM-41, showing the effect of Fe content 332 Figure 5.23 Light-off curves for uncalcined 1.5 wt% Au/Me-MCM-41 materials (Me = Fe or Co) prepared by coprecipitation in the presence of Si-MCM-41, showing the effect of metal identity on the activity of the catalyst 333 xxix LIST OF TABLES CHAPTER 1 Table 1.1 Composition of synthesis mixtures for the formation of various M41S phases 4 Table 1.2 Iron contents and H2 consumption of different Fe-MCM-41 samples 38 CHAPTER 2 Table 2.1 Room temperature synthesis of Si-MCM-41: ao versus synthesis time 107 Table 2.2 Effect of gel SiO2/CTAB mole ratio on the structure of Si-MCM-41 109 Table 2.3 XRD properties of sec-Si-MCM-41 (100 oC for 4 days) 128 Table 2.4 BET surface area (SBET) versus crystallization temperature (3 days synthesis) for Si-MCM-41 136 Table 2.5 Si-MCM-41 properties: Effect of mineral acid identity 139 Table 2.6 The effect of additives to the synthesis gel on the surface area of Si- MCM-41 140 Table 2.7 Effect of gel RSiO2 on SBET of Si-MCM-41 140 CHAPTER 3 Table 3.1 Effects of Fe loading on the XRD properties of Fe-MCM-41 prepared by IWI 170 Table 3.2 Effect of calcination temperature on impregnated 16 wt% Fe-MCM-41 170 Table 3.3 XRD data for 16 wt% Fe-MCM-41 made with calcined Si-MCM-41 (which was made from a mixture of fumed SiO2 and water-glass as SiO2 source) as SiO2 source 177 Table 3.4 XRD data for 16 wt% Fe-MCM-41 made with calcined Si-MCM-41 (which was made from only water-glass as SiO2 precursor) as SiO2 source 177 Table 3.5 HNO3-assisted Co(II) incorporation into the MCM-41 synthesis gel, and its effect on the properties of the resulting Co-MCM-41 materials 183 xxx Table 3.6 Variation of the lattice parameter (ao) of 16 wt% Fe-MCM-41 with the identity of the precipitant for Fe(III) 186 Table 3.7 Variation of the lattice parameter and BET surface area of Fe-MCM-41 with the Fe content. The materials were calcined at 560 oC for 6 h 188 Table 3.8 Variation of ao and SBET with Co content for Co-MCM-41 prepared via the OH- route at 100 oC for 2 days (calcined at 560 oC for 6 h) 190 Table 3.9 XRD and BET surface area data for 16 wt% Me-MCM-41 (Me = Si, Fe, Co and Ru) prepared by the metal hydroxide route at different temperatures 195 Table 3.10 A comparison of ao values of 16 wt% Fe- and Co-MCM-41 as influenced by the synthesis method 196 Table 3.11 Assignment of IR vibrational peaks in the Fe-containing MCM-41 materials in Figure 3.63 234 CHAPTER 4 Table 4.1 Representative characterization techniques for supported Au catalysts 255 Table 4.2 Variation of SBET for Au/Me-MCM-41 (Me = Si, Co and Fe) 265 Table 4.3 Surface areas of the Au-containing samples 266 Table 4.4 (a) One-pot synthesized Au-containing materials calcined at 500 oC for 12 h 284 Table 4.4 (b) Post-synthetically prepared Au-containing MCM-41 prepared via en route. Calcination was done at 400 oC for 4 h, unless stated otherwise 285 Table 4.4 (c) Other post-synthesis methods for Au-containing materials 285 CHAPTER 5 Table 5.1 WGC Reference Gold Catalysts 301 Table 5.2 Correlation of preparation method, Au particle size and catalytic activity for Au/Si-MCM-41 catalysts 312 Table 5.3 Activity and other properties of Au on 5 wt% Co-MCM-41 catalysts 314 Table 5.4 Activity and physical properties of 1-5 wt% Au/3 wt% Fe-MCM-41 318 xxxi Table 5.5 Activity and physical property data for 5 wt% Au on 0-5 wt% Fe- MCM-41 320 Table 5.6 Correlation of activity with physical properties of 5 wt% Au on different supports (Fe- and Co-modified MCM-41) 325 Table 5.7 Activation energy (Ea) for Au/ Me-MCM-41 (Me = Si, Fe and Co) 327 CHAPTER 6 Table 6.1 Lattice parameters and BET data for 16 wt% Me-MCM-41 (Me = Fe, Co, Ru) 352 xxxii LIST OF ABBREVIATIONS AND ACRONYMS AAS Atomic Absorption Spectrometry BET Brunnauer-Emmett-Teller BJH Barrett-Joyner-Halenda BMS Bimodal silica CIT-5 California Institute of Technology number 5 CO Carbon monoxide CMC Critical micelle concentration CMK Carbon Mesostructures at KAIST CP Coprecipitation COHb Carboxyhemoglobin CTAB Cetyltrimethylammonium bromide CTMAOH Cetyltrimethylammonium hydroxide CVD Chemical vapour deposition DAM-1 Dallas Amorphous Material # 1 DP Deposition-precipitation DRIFTS Diffuse Reflectance Infrared Fourier Transform Spectroscopy DRS UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis) DTA Differential Thermal Analysis EDS Energy-dispersive X-ray spectrometry EDTA Ethylenediamine tetraacetate EDX Energy-dispersive X-ray Analysis EHC Electrically heated catalyst en Ethylenediamine xxxiii EPA Environmental Protection Agency EPR Electron Paramagnetic Resonance ESR Electron Spin Resonance EXAFS Extended X-ray Absorption Fine Structure FMMS Functionalized Monolayers on Mesoporous Supports FMS-16 Folded Sheet Mesoporous material, 16 designates a 16 C surfactant template (FT)IR Fourier Transform Infrared FTS Fischer-Tropsch Synthesis g Lande factor or gyromagnetic ratio HCs Hydrocarbons HDP Homogeneous deposition-precipitation HDS Hydrodesulphurization HMS Hexagonal mesoporous silica (HR)TEM High resolution transmission electron microscopy (HR)SEM High Resolution Scanning Electron Microscopy ICP Inductively-coupled plasma IEC Ion exchange capacity IEP Isoelectric point IUPAC International Union of Pure and Applied Chemistry IWI Incipient wetness impregnation KAIST Korea Advanced Institute of Science and Technology LAT Ligand-assisted templating LCT Liquid-crystal templating MCM Mobil?s Composition of Matter xxxiv MFI Mobil Five MSU-G, -X Michigan state university-G or X MTS Micelle-templated silica NOx Nitrogen oxides NMR Nuclear Magnetic Resonance O2Hb Oxyhemoglobin OMS Ordered Mesoporous Silica ORMOSILs Organically-Modified Silicas PE Polyethylene PP Polypropylene PGMs Platinum Group Metals PHCs Porous Clay Heterostructures PILCs Pillared Clays PNNL Pacific Northwest National Laboratory PSD Particle size distribution PVD Physical Vapour Deposition PZC Point of Zero Charge RS Raman spectroscopy SAMMS Self-Assembled Monolayers on Mesoporous Supports SBA Santa Barbara SCTA Sample Controlled Thermal Analysis SDA Structure-directing agent SFE Supercritical Fluid Extraction SIB Ship-in-a-bottle xxxv SMSIs Strong metal-support interactions SV Space velocity T50 Light-off temperature TBHP Tertiarybutylhydroperoxide TCD Thermal conductivity detector TEA Triethanolamine TEOS Tetraethyl orthosilicate TGA Thermogravimetric analysis TIE Template ion-exchange TMCS Trimethyl chlorosilane TMMPS Tris(methoxy)mercaptopropylsilane TMOS Tetramethyl orthosilicate TMS-1 Transition-metal mesoporous molecular sieves TOS Time on stream TPGS ?-Tocopheryl polyethylyne glycol 1000 succinate TPR Temperature-Programmed Reduction TUD-1 Technical University of Delft # 1 TWC Three-way catalyst USY Ultrastable Y zeolite UTD University of Texas at Dallas UV-Vis Ultraviolet and Visible spectrophotometry VAM Vinyl acetate monomer VPI-5 Virginia Polytechnic Institute # 5 XANES X-ray Absorption Near-Edge Spectroscopy xxxvi XPS X-ray Photoelectron spectroscopy XRD X-ray diffraction XRF X-ray fluorescence WGC World Gold Council WGS Water-gas shift ZSM-5 Zeolite Saucony Mobil # 5 xxxvii SCOPE AND CONTENT OF THE THESIS Pure silica has a neutral framework in which the Si4+ is tetrahedrally bonded to four bridging O atoms, and consequently cannot show cation exchange properties. Metal components can be introduced into the silica to induce cation exchange capacity, redox properties and nucleation sites for the growth or development of metal nanoparticles. This thesis examines Si-MCM-41 and metal-containing variants, i.e., Fe- and Co-MCM-41 as supports for Au catalysts. Au catalysts have recently gained popularity because of their ability to catalyze a wide range of reactions at low temperature. Chapter 1 covers the literature on inorganic porous materials, with particular reference to addressing the issue of shape selectivity in microporous materials and improving the surface area of the resulting materials. The survey includes a discussion of the first templated synthesis of a mesoporous family of zeolitic materials, designated M41S, to which belong a range of interesting materials such as MCM-41, MCM-48 and MCM-50. The survey includes the synthesis, characterization, catalytic and technical applications of the Si-MCM-41 materials. Chapter 2 presents the results of the work carried out on pure silica MCM-41 materials that were prepared in this thesis. Covered in this study are the role of various synthetic variables (i.e. optimization of the synthesis conditions) that lead to a highly ordered Si-MCM-41 with improved structural integrity, as well as enhanced thermal and hydrothermal stability. These variables include the crystallization time and reaction temperature, the synthesis gel composition (SiO2/CTAB molar ratio and the water content), inclusion of additives as co- templates in the synthesis gel, the pH of the synthesis gel, and the nature of the silica source. These materials were characterized using X-ray diffraction (XRD) to assess structural integrity, High Resolution Transmission Electron Microscopy (HRTEM) to evaluate the microstructure of the pores, and Brunauer-Emmett- Teller (BET) surface area analysis. Conclusions at the end of the chapter are based on the findings of these characterization techniques. The optimized Si-MCM-41 xxxviii materials so obtained were used as benchmarks in the synthesis of base metal- containing mesoporous MCM-41 materials described in chapter 3. Chapter 3 focuses on Fe- and Co-MCM-41 materials, with particular emphasis on their synthesis and characterization. The metal precursors were introduced at various stages of the synthesis, and in various forms (i.e., as solutions or as freshly-prepared gelatinous precipitates). The synthesis was carried out under both ambient and hydrothermal temperature conditions, and the amount of the heterometal that was incorporated into the mesostructure with structural retention has been optimized. Incipient wetness impregnation was also used for the synthesis of Fe- and Co-MCM-41 derivatives. Physicochemical characterization of the resulting materials included XRD, HRTEM, BET, temperature programmed reduction (TPR), ESR spectroscopy and Raman spectroscopy. Conclusions are also included at the end of this chapter, based on the observations from these characterization techniques. These heteroatom-containing mesoporous materials, with their associated redox and cation exchange properties, were used as supports in the preparation of supported Au catalysts discussed in chapter 4. Chapter 4 focuses on an investigation of different methods used to prepare supported gold nanoparticles. These methods range from deposition-precipitation, co-deposition-precipitation (both Fe(III) or Co(II) and Au(III) deposited simultaneously on Si-MCM-41), co-precipitation of Au(III) with either Fe(III) or Co(II) in the presence of a preformed Si-MCM-41, or direct one-pot hydrothermal synthesis where the metal components form part of the initial synthesis gel. Characterization of the final materials involved XRD, HRTEM, BET and EDS techniques. These materials and other related materials were evaluated for catalytic activity as described in chapter 5. Chapter 5 describes the catalytic properties of the Au/Me-MCM-41 materials, with Me = Si, Fe and Co, in the reaction: 2 CO(g) + O2(g) ? 2 CO2(g), ?G298 K = -257.1 kJ/mol xxxix The results are interpreted in terms of the light-off temperature, i.e., the temperature at which the catalyst starts converting carbon monoxide into carbon dioxide. Conclusions based on the observed catalytic behaviour are found at the end of the chapter. Chapter 6 presents the summary of the work done, and the main conclusions of the study entailed in this thesis.