What is the effect of Sn and Mo oxides on gold catalysts for selective oxidation of benzyl alcohol?

Abstract

A foam-like mesoporous silica (MCF)-supported gold (Au) nanoparticle (NP) catalyst was prepared by a facile one-pot synthesis strategy. SnO_x and MoO_x were introduced as promoters by a wet impregnation method to synthesize promoted catalysts Au–SnO_x/MCF and Au–MoO_x/MCF, respectively. The evaluation of the prepared catalysts in benzyl alcohol oxidation shows that introduction of a low amount of SnO_x (0.2 wt%) leads to a higher catalytic activity, while a relatively high amount of SnO_x (1.0 wt%) exhibits a lower catalytic activity than the unpromoted Au NP catalyst. Both characterization results and density functional theory (DFT) calculations suggest that the most important effect of SnO_x species on gold catalysts is the strong interaction between them which leads to electron transfer and lattice distortion of Au NPs, providing more low-coordinated Au active sites. This structural modification enhanced the chemisorption of reactants and lowered the energy barrier for the dissociation of O₂ molecules on the surface of gold catalysts, improving the catalytic performance for benzyl alcohol oxidation. However, a weaker interaction was detected between MoO_x and Au NPs on catalysts Au–MoO_x/MCF and no lattice modification was observed; thus no improvement in the catalytic activity for benzyl alcohol oxidation occurred on catalysts Au–MoO_x/MCF.