CO2 conversion and reuse technology are crucial for alleviating environmental stress and promoting carbon cycling. Reverse water gas shift (RWGS) reaction can transform inert CO2 into active CO. Molybdenum carbide (MoC) has shown good performance in the RWGS reaction, and different crystalline phases exhibit distinct catalytic behaviors. Here, we performed a systematic study on the RWGS reaction mechanism on the hexagonal-phase γ-MoC(100) surface by using density functional theory (DFT). It is found that the redox mechanism, i.e. the direct dissociation of CO2, is the dominant pathway. CO2 firstly adsorbs on the surface with an adsorption energy of -2.14 eV, and then dissociates into CO* and O* with a barrier of 0.83 eV. Surface O* hydrogenating into OH* has a high barrier of 2.15 eV. OH* further hydrogenating into H2O* has a barrier of 1.48 eV, and the disproportionation of OH* considerably lowers this value to 0.06 eV. However, the desorption of product CO is particularly challenging due to the large energy demand of 3.06 eV. This characteristic, in turn, provides feasibility and opportunity for CO2 to serve as a potential alternative carbon source for CO on the γ-MoC(100) surface. In contrast, other Mo-based catalysts such as hexagonal MoP and cubic α-MoC have better RWGS catalytic efficiency.
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