CO 2 adsorption and activation over γ-Al 2O 3-supported transition metal dimers: A density functional study

Abstract

Catalytic conversion of CO 2 to liquid fuels has the benefit of reducing CO 2 emission. Adsorption and activation of CO 2 on the catalyst surface are key steps of the conversion. Herein, we used density functional theory (DFT) slab calculations to study CO 2 adsorption and activation over the γ-Al 2O 3-supported 3d transition metal dimers (M 2/γ-Al 2O 3, M = Sc–Cu). CO 2 was found to adsorb on M 2/γ-Al 2O 3 negatively charged and in a bent configuration, indicating partial activation of CO 2. Our results showed that both the metal dimer and the γ-Al 2O 3 support contribute to the activation of the adsorbed CO 2. The presence of a metal dimer enhances the interaction of CO 2 with the substrate. Consequently, the adsorption energy of CO 2 on M 2/γ-Al 2O 3 is significantly higher than that on the γ-Al 2O 3 surface without the metal dimer. The decreasing binding strength of CO 2 on M 2/γ-Al 2O 3 as M 2 changes from Sc 2 to Cu 2 was attributed to decreasing electron-donation by the supported metal dimers. Hydroxylation of the support surface reduces the amount of charge transferred to CO 2 for the same metal dimer and weakens the CO 2 chemisorption bonds. Highly dispersed metal particles maintained at a small size are expected to exhibit good activity toward CO 2 adsorption and activation.