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.