Computational identification of facet-dependent CO2 initial activation and hydrogenation over iron carbide catalyst

Abstract

χ-Fe5C2 is a promising candidate catalyst for hydrocarbons synthesis through CO2 hydrogenation, however, surface structure reconstruction of the catalyst occurs under reaction conditions which impacts the catalytic performance. In this work, the facet-dependent catalytic behavior of χ-Fe5C2 toward CO2 initial activation and hydrogenation was revealed by density functional theory calculations. Among the six studied facets of χ-Fe5C2, the (510) surface was found to be more active for CO2 activation via direct dissociation to CO* +O* (barrier of 0.24 eV) whereas on the (111) surface, CO2 hydrogenation to HCOO* intermediate was kinetically most favorable with a small barrier of 0.25 eV. Both (510) and (111) facets are good candidates for CO2 initial activation and transformation although the conversion pathways are different. The (110) facet of χ-Fe5C2 is inactive toward CO2 initial activation and conversion due to large barriers. As identified in the literature that the (111) facet of χ-Fe5C2 is more active toward C2 formation via C-C coupling in Fischer-Tropsch synthesis, this surface should also be a good candidate for hydrocarbons synthesis from CO2 hydrogenation as demonstrated in this work. This study fills in gaps in the understanding of facet and surface structure effect of single-phase iron carbide catalysts on CO2 activation and transformation, and offers important insight into the design of improved CO2 hydrogenation catalysts.