The effect of metal support interactions between a cobalt catalyst and carbon dots (Cdots) in cobalt fischer-tropsch catalysts

Mokoloko, Lerato Lydia
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The aim of this study was to introduce functionalized carbon dots (Cdots) as potential support and reducing agents for cobalt-based Fischer-Tropsch catalysts. Cdots with different physicochemical properties were synthesized from natural-based product such as ascorbic acid, sucrose and chitosan, using microwave-assisted reactions. Two types of Cdots, namely N-free Cdots (or Cdots) and N-doped Cdots, with particle sizes < 10 nm were produced. Both Cdots and N-doped Cdots have an amorphous structure, containing both sp2 and sp3 type carbon. The surface of Cdots contained mainly hydroxyl and carboxyl functional groups, while N-doped Cdots contained hydroxyl, carbonyl, and nitrogen-based (mainly pyridinic and pyrrolic) functional groups. Spinel Co3O4 nanoparticles with 10 nm crystallite sizes were synthesized from the “benzyl alcohol route”. Both the spinel Co3O4 nanoparticles and functionalized Cdots were used to prepare the inverse Co3O4/Cdots and Co3O4/N-doped Cdots catalysts. The in-situ XRD results showed that under H2 gas reduction conditions, the Co3O4/Cdots and Co3O4/N-doped Cdots catalysts increased the reduction temperature of Co3O4 to CoO and metallic Co, and Co (fcc) is the predominant form of metallic Co formed. However, when N-doped Cdots were used as both support and reducing agents, Co3O4 was reduced to both Co (fcc) and Co (hcp). The increase in reduction temperature of Co3O4 on Co3O4/Cdots and Co3O4/N-doped Cdots suggest the presence of strong metal to support interactions (SMSIs) between Co3O4 and functionalized Cdots. Further studies on the activity and selectivity of these prepared catalysts will be conducted under F-T reaction process.
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment for the degree of Master of Science in Chemistry. University of the Witwatersrand, Johannesburg, January 2018
Mokoloko, Lerato Lydia (2018) The effect of metal to support interactions between a cobalt catalyst and carbon dots (Cdots) in cobalt Fischer-Tropsch catalysts, University of the Witwatersrand, Johannesburg, <>