Computational investigation of Fe-Cu bimetallic catalysts for CO₂ hydrogenation

Density functional theory (DFT) calculations were carried out to investigate Fe-Cu bimetallic catalysts for the adsorption, activation, and initial hydrogenation of CO₂. CO₂ adsorption strength decreases monotonically as surface Cu coverage increases. For dissociation of CO₂, the reaction energy and activation barrier scale linearly with surface Cu coverage. The reaction energy becomes less exothermic, and the activation barrier increases with increasing surface Cu coverage from 0 to 1 ML. For initial hydrogenation of CO₂, formation of a formate (HCOO∗) intermediate is kinetically favored over carboxyl (COOH∗) at all surface Cu coverages. A substantial decrease of the kinetic barrier for HCOO∗ formation is observed when surface Cu coverage increases to 4/9 ML. CO∗ is the preferred intermediate from CO₂ dissociation at 2/9 ML surface Cu coverage or below; however, the favorable conversion path changes to CO₂ hydrogenation to a HCOO∗ intermediate when surface Cu coverage increases to 4/9 ML or higher. The composition and structure of the bimetallic catalysts determine the preferred intermediates and dominant reaction paths for CO₂ conversion, and thus, both impact the catalytic activity and selectivity.