Compatibility between Activity and Selectivity in Catalytic Oxidation of Benzyl Alcohol with Au-Pd Nanoparticles through Redox Switching of SnO.

A balance between catalytic activity and product selectivity remains a dilemma for the partial oxidation processes because the products are prone to be overoxidized. In this work, we report on the partial oxidation of benzyl alcohol using a modified catalyst consisting of nanosized Au-Pd particles (NPs) with tin oxide (SnO) deposited on a mesoporous silica support. We found that the SnO promotes the autogenous reduction of PdO to active Pd species on the Au-Pd NP catalyst (SnO@AP-ox) before H reduction, which is due to the high oxophilicity of Sn. The presence of active Pd species and the enhancement of oxygen transfer by SnO led to high catalytic activity. The benzaldehyde selectivity was enhanced with the increase of SnO content on catalyst SnO@AP-ox, which is ascribed to the modulated affinity of reactants and products on the catalyst surface through the redox switching of Sn species. After H reduction, SnO was partially reduced and Au-Pd-Sn alloy was formed. The formation of Au-Pd-Sn alloy weakened both the catalytic synergy of Au-Pd alloy NPs and the adsorption of benzyl alcohol on the reduced catalyst, thus leading to low catalytic activity.