Mechanistic Understanding of Hydrocarbon Formation from CO2 Hydrogenation over χ-Fe5C2(111) and the Effect of H2O and Transition Metal Addition

Converting CO2 into a range of chemicals and fuels is an effective approach to address excessive CO2 emissions. In this work, density functional theory (DFT) calculations were performed to investigate the reaction mechanism of hydrocarbons formation from CO2 hydrogenation on the surface of chi-Fe5C2 (111). Optimal energetic pathways, key reaction intermediates (such as CO*, H2COH*, and CH2*), and rate-liming steps were identified for the production of CH4 and C2H4. The calculation results revealed that H2O* species formed on the surface of chi-Fe5C2 (111) significantly reduced the barriers of the O-H bond formation step, altering reaction pathways and promoting CO2 conversion kinetics. Importantly, it was identified that the introduction of a second transition metal, such as Cr, Mn, Pd, or Zn, into chi-Fe5C2 (111) could regulate the surface C/H ratio and product desorption rate, effectively tuning the product selectivity.