Adsorption and activation of CO2 over the Cu–Co catalyst supported on partially hydroxylated γ-Al2O3

A multi-component catalyst offers an opportunity to regulate the conversion of CO2 toward the desired product through the synergistic effect of different active components. Herein, the effect of incorporating Cu into a cobalt-based cluster, supported on the partially hydroxylated γ-Al2O3 (1 1 0) surface, on CO2 adsorption has been studied using periodic density functional theory calculations. Three CO2 adsorption modes were identified on these Co–Cu bimetallic clusters: (a) CO2 symmetrically binds the bridge site of the metals through mixed carbon/oxygen coordination with the metal atoms; (b) CO2 asymmetrically adsorbs at the interfacial site via carbon/oxygen–metal coordination and hydrogen bonding to the surface hydroxyl; and (c) protonated CO2 at the interface. The incorporation of Cu into a cobalt-based cluster reduces the binding strength of the adsorbed CO2 and changes the favorable site of CO2 adsorption: the most favorable adsorption site for CO2 adsorption changes from the bridge site of the Co4 cluster to the interfacial sites of the Co3Cu and CoCu3 clusters. The interfacial structure is stabilized by hydrogen bonding with the surface hydroxyl group, resulting in an asymmetrically activated CO2 adsorption complex. This complex may be hydrogenated directly by the co-adsorbed hydrogen atoms, leading to the oxygenate products.