CO2 DISSOCIATION ON Ni-RICH MULTIMETAL CLUSTER: EFFECT OF Pt AND Mg

Density functional theory (DFT) calculations were used to perform the mechanistic studies of CO2 dissociation into CO and O on Ni4, Ni3Pt, and Ni2PtMg clusters. Optimizations of initial, transitional, and final states were performed for all cases. Molecule orbital analysis showed that Pt and Mg possess fine electron donating ability while Ni possesses fine electron accepting ability. CO can chemisorb on all metallic sites and binds more weakly on the Mg atom of a Ni2PtMg cluster, with adsorption energy of -0.42 eV. Energy barrier for CO2 dissociation on Ni4 is 2.07 eV. However, this value can scarcely decease to 1.85 eV when a Pt atom replaces one Ni atom in the Ni4 cluster. The addition of Mg could decrease the energy barrier of CO2 dissociation on the Ni2PtMg cluster without Mg directly involved in the reaction, and the energy barrier decreased to 1.23 eV. When Mg atom is directly involved in the reaction, the energy barrier for CO2 dissociation is as low as 0.48 eV. However, the weak binding energy of CO with Mg is not beneficial to the subsequent reactions. As a result, the addition of Mg and Pt improves the activity of Ni4 cluster for CO2 dissociation, which is consistent with the previous experimental results.