Unveiling the critical role of p-d hybridization interaction in M13−nGan clusters on CO2 adsorption

Abstract

Inspired by conclusions of previous studies that Ga has the promoting effect on CO2 conversion, we performed density functional theory (DFT) investigations of CO2 adsorption on forty icosahedral (Ih) symmetry 13-atom clusters. They include M13, Ga-centered M12Ga, M-centered M12Ga, Ga-centered M11Ga2 and M-centered M11Ga2 clusters (M = Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag). Initially, the stabilities of these clusters were studied. The results show that Ga doped Cu, Pd, and Ag clusters are more stable than their pure metal analogues, and except Pd and Ag clusters, M-centered species are more stable than Ga-centered clusters. In addition, the activation of CO2 on these clusters was studied. The results show that most of M-centered M12Ga clusters transfer more electron density to CO2 than other corresponding Ga-doped analogues. The amount of Bader charge transfers has noteworthy linear relationship with the structural parameters of CO2. DOS analyses show that empty σ orbital of CO2 is acceptor of electrons from cluster. It is worth to mention that Ag13−nGan clusters have little interaction with CO2. To explain the effects of Ga on the adsorption of CO2, the electronic properties of clusters were studied. The projected density of states (PDOSs), charge density differences, Bader charge transfers and electron localization functions (ELFs) analyses show that Ga transfers electron density to M atom, and the effective interaction is attributed to the p orbitals of Ga with the d orbitals of M near Fermi level(0), mainly responsible for the activation of CO2.