Catalytic performance of Pdn (n = 1, 2, 3, 4 and 6) clusters supported on TiO2-V for the formation of dimethyl oxalate via the CO catalytic coupling reaction: a theoretical study

Abstract

The formation of dimethyl oxalate (DMO) via CO catalytic coupling on a series of catalysts including Pd_n (n = 1, 2, 3, 4 and 6) clusters loaded on TiO_2-V has been explored by density functional theory (DFT) calculation. The results show that different Pd_n clusters have a remarkable influence on DMO formation. The Pd₁/TiO_2-V catalyst is not suitable for the CO catalytic coupling reaction since CO is easily bound to the O atom on the surface of TiO_2-V leading to the formation of CO₂. The activity of four catalysts complies with the following order of Pd₄/TiO_2-V > Pd₆/TiO_2-V > Pd₂/TiO_2-V > Pd₃/TiO_2-V by comparing the activation energy barriers of the rate-determining steps in the optimal paths. Charge analysis implies that less charge is transferred from the Pd₄/TiO_2-V and Pd₆/TiO_2-V catalysts to CO than on the other catalysts, which leads to the relatively weak adsorption of CO, and therefore CO has a greater tendency to react with other species on the surface. In addition, Pd₆/TiO_2-V also exhibits relatively higher selectivity toward DMO than the other three catalysts. Therefore, Pd₆ is regarded as a suitable cluster, which is supported on TiO_2-V demonstrating high catalytic activity and selectivity to DMO.