Mechanism of CO2 hydrogenation over θ-Fe3C catalyst: First-principles calculations combined with micro-kinetic modeling

Catalytic conversion of carbon dioxide into high-value compounds is a promising strategy for reducing carbon dioxide emissions. In the reduction of CO2 to hydrocarbons, the active point and reaction mechanism of iron-based catalysts are still unclear. Here, we systematically investigated the complete reaction path of carbon dioxide hydrogenation to methane, ethylene, ethane, and carbon monoxide over the theta-Fe3C(031) surface using first principles calculations. The electronic structure analysis shows that carbon dioxide tends to dissociate directly on the theta-Fe3C(031) surface to form CO* instead of COOH* and HCOO* intermediates. Due to the high energy barrier for CO* hydrogenation, it tends to desorb forming CO product instead of further transformation into hydrocarbons. In addition, the microkinetic model proved that the H* species coverage on the theta-Fe3C(031) crystal surface is highly, which could effectively inhibit the further oxidation of the catalyst, indicating the catalyst to be highly stable. Meanwhile, carbon monoxide behaved the highest relative selectivity. These results reveal the key intermediates and reaction paths of carbon dioxide hydrogenation over theta-Fe3C(031) catalyst surface and further illustrate the key factors affecting its product selectivity, providing a theoretical basis and guidance for the design and synthesis of the catalyst.