Tuning the Reaction Mechanism toward Selective Hydrogenation of CO2 to Formic Acid on a Sn10O20 Cluster

Mitigation of CO2 and its conversion into valuable chemicals is obligatory as continuous emission of CO2 is a serious threat to global climate change and hence to living beings. Herein, we have studied the catalytic behavior of magic cluster Sn10O20 toward the reduction of CO2 to formic acid (FA) using the density functional theory (DFT) method. Two possible pathways have been explored for the conversion. First, the dissociation of H-2 on the cluster offers a route where Sn hydride triggers the selectivity of formic acid formation via a HCOO* intermediate. Second, in the coadsorption pathway, as a result of the polarization effects of the 'O' of the O-2C4 active site, H-2 gets activated and forms a stable six-membered ring in the transition state to give a direct HCOO* intermediate. In the transition state, the 'H' in the newly formed "C-H" bond is also characterized as a hydride with the Bader charge of -0.19 |e|, and it holds the selectivity of formic acid. Among the two pathways, the coadsorption pathway proves to have better catalytic efficiency by providing a lower energetic pathway than the Sn-hydride-assisted pathway. Our results and analyses reveal that the reduction pathway changes to get better selectivity from the small SnO2 to the larger-sized Sn10O20. It is also noteworthy to mention that catalytic efficiency depends upon the coordination number of "Sn" in the clusters.