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

CO2hydrogenation to methanol on small size Pdxclusters(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 Pdxclusters can interact well with CO2molecule. CO2molecule can be adsorbed with a bidendate configuration on the Pdxclusters. The formation of CO2bidendate adsorption configuration facilitates the first step of CO2hydrogenation reaction on the clusters. The energy profiles for formate pathway and reverse water gas shift + CO hydrogenation pathways on Pdxclusters are quite similar with Cu(111) surface, except for the first and last hydrogenation steps where the Pdxclusters have lower activation energies. This improvement causing the Pdxclusters 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 CO2hydrogenation to methanol because small size Pd cluster can act not only as an H2dissociation center but also as a CO2hydrogenation center.