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

Abstract

Converting CO 2 into a range of chemicals and fuels is an effective approach to address excessive CO 2 emissions. In this work, density functional theory (DFT) calculations were performed to investigate the reaction mechanism of hydrocarbons formation from CO 2 hydrogenation on the surface of χ-Fe 5 C 2 (111). Optimal energetic pathways, key reaction intermediates (such as CO*, H 2 COH*, and CH 2 *), and rate-liming steps were identified for the production of CH 4 and C 2 H 4 . The calculation results revealed that H 2 O* species formed on the surface of χ-Fe 5 C 2 (111) significantly reduced the barriers of the O−H bond formation step, altering reaction pathways and promoting CO 2 conversion kinetics. Importantly, it was identified that the introduction of a second transition metal, such as Cr, Mn, Pd, or Zn, into χ-Fe 5 C 2 (111) could regulate the surface C/H ratio and product desorption rate, effectively tuning the product selectivity.

Mechanistic Study on the Possibility of Converting Dissociated Oxygen into Formic Acid on χ-Fe5C2(510) for Resource Recovery in Fischer–Tropsch Synthesis

“…There are two ways to attempt to remove dissociated oxygen in the form of formic acid, based on the reaction mechanism that limits the formation of formic acid. Firstly, the ability of the catalyst to adsorb carbon dioxide and the possibility of a carbon dioxide hydrogenation reaction can be improved by modifying the iron-based catalyst with other elements, which can be considered as the introduction of elements such as Cr, Mn, and Pd [52]. Secondly, by increasing the CO coverage on the catalyst surface while decreasing the hydrogen coverage, the likelihood of OH species undergoing a hydrogenation reaction is reduced.…”