The increasing concentration of CO2 in the atmosphere has caused global warming, ocean acidification and many environmental issues. Among the different approaches to convert CO2, the hydrogenation of CO2 to valuable products such as gasoline and liquid fuels has attracted great attention. Iron based catalysts are widely used for hydrocarbon synthesis from CO2 hydrogenation. The iron oxide is considered as the active site for water-gas shift reaction. The χ-Fe5C2 and θ-Fe3C are the main active species in Fischer-Tropsch synthesis. In the previous work by Pham and Wang, their DFT results showed low C-C coupling barriers for C2 hydrocarbon formation over χ-Fe5C2 and θ-Fe3C catalysts during FTS. The active sites for CO2 activation and hydrogenation over Fe-based catalysts remains unclear. In this work, we performed density functional theory (DFT) calculations to investigate CO2 adsorption, activation and hydrogenation over iron carbide and oxide catalysts, in combination with micro-kinetic modeling. The reaction pathways and elementary energetics for CH4 and C2 hydrocarbons formation on χ-Fe5C2(510) and θ-Fe3C(031) were discussed in terms of C-O bond activation, C-H bond formation, and C-C coupling. The potential energy surface for CO formation from CO2 hydrogenation on Fe3O4(111) was established. Based on DFT-determined energies, the micro-kinetic modeling was conducted to unravel the rate limiting step and reaction rates for CO2 hydrogenation to hydrocarbons. We will discuss the active sites and reaction pathways. These results will aid for future design of the selective Fe-based catalysts for CO2 conversion.

Activation and hydrogenation of CO2 over iron carbide and oxide catalysts: Insight from DFT

255th National Meeting (2018)

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