Theoretical study of CO2 hydrogenation to methanol on isolated small Pd clusters

Abstract

Abstract CO2 hydrogenation to methanol on small size Pdx clusters (x = 7, 9 and 13) has been studied using density functional theory calculations. It has been found that in contrast to metallic Pd system, these small Pdx clusters can interact well with CO2 molecule. CO2 molecule can be adsorbed with a bidendate configuration on the Pdx clusters. The formation of CO2 bidendate adsorption configuration facilitates the first step of CO2 hydrogenation reaction on the clusters. The energy profiles for formate pathway and reverse water gas shift + CO hydrogenation pathways on Pdx clusters are quite similar with Cu(111) surface, except for the first and last hydrogenation steps where the Pdx clusters have lower activation energies. This improvement causing the Pdx clusters to have a tolerable turn over frequencies values. In general, the usage of Pd in the form of small size cluster can improve the catalytic performance of metallic Pd for the CO2 hydrogenation to methanol because small size Pd cluster can act not only as an H2 dissociation center but also as a CO2 hydrogenation center.