Transition Metal Carbides for Thermocatalytic Conversion of Carbon Dioxide via Reverse Water Gas Shift and Sabatier Reactions

Abstract

The conversion of carbon dioxide (CO2) to synthetic fuels and chemicals is seen as a promising approach for reducing greenhouse gas emissions. Syngas (a mixture of CO and H2) that can be obtained from CO2 via the reverse water gas shift (RWGS) reaction can be further processed through the Fischer Tropsch process to produce higher hydrocarbons. Synthetic natural gas (CH4) produced from the Sabatier reaction can help reducing consumption of fossil fuel and also can serve as an energy reservoir for renewable electricity via power-to-gas. However, utilization of the abovementioned reaction pathways is still limited due to various challenges including catalyst activity, selectivity, and stability. This thesis focuses on the development of catalytic materials for the RWGS and Sabatier reactions.

The first part of this thesis first focuses on a literature overview of recent developments in CO2 conversion through the RWGS and Sabatier reaction. Then, the experimental setup, catalyst synthesis procedures, catalytic performance evaluation, and characterization techniques are outlined.

The second part discusses the results of the two transition metal carbides tested, namely molybdenum carbide (Mo2C) and cobalt carbide (Co2C). The catalytic performance of these catalysts was evaluated as a function of operation parameters for different synthesis procedures. The mechanisms of catalytic reactions are postulated and catalyst characterization results are provided.

To briefly outline the most important findings, the Mo2C catalyst showed nearly complete selectivity towards CO formation at all temperatures tested, whereas the Co2C catalyst appeared to be highly selective towards CH4 formation. The performance of the corresponding metal oxides are also evaluated to evaluate the effect of carburization on the performance of the catalyst. The transitions metal oxides of molybdenum and cobalt both showed a substantial improvement in both conversion and selectivity after the carburization process. The performance of the catalysts supported on Al2O3 at a 1:4 metal-to-support basis was also analyzed. During the stability tests of supported catalysts, CO2 conversions of 84% and 74% were recorded over the Mo2C and Co2C catalysts, respectively, with a negligible drop in catalytic performance after 42 and 64 h time on stream.