Theoretical study about adsorbed oxygen reduction over χ-Fe5C2: formation of H2O and CO2

Abstract

The removal of surface oxygen adsorbed on iron carbides is essential to protect the nanoparticle from oxidation in heterogeneous catalysis. Herein, we explored the removal of pre-adsorbed oxygen on seven facets of χ-Fe5C2, and four pathways including both direct and indirect routes for generating H2O and CO2 were investigated. The removal mechanism shows diversity over different facets. On (010), the formation of CO2 through the reaction between surface oxygen and adsorbed CO is more favorable. While on (510), (001), (110), (11-1) and (-411), the elimination in the form of H2O through OH disproportionation dominates. In particular, surface oxygen can be removed facilely either in H2O or CO2 on (111) surface. What's more, surface with more carbons exhibits higher barriers to direct CO2 formation, like (110) and (111). Our work provides knowledge about mechanism of O removal and CO2 formation, which may be helpful in protecting the nanoparticle from further oxidation.