Visible light-driven oxidation of vanillyl alcohol in air with Au–Pd bimetallic nanoparticles on phosphorylated hydrotalcite

Abstract

The selective photocatalytic oxidation of vanilla alcohol with air was studied preliminarily using supported Au–Pd bimetallic nanocatalysts. The support, phosphate-modified Mg–Al hydrotalcite (HT-PO₄³⁻), was produced first with a sol–gel and ion-exchange method, and then Au–Pd alloy nanocatalysts supported on activated carbon (C) and HT-PO₄³⁻ were prepared, respectively, by an impregnated-reduction approach. Subsequently, the morphology and property of these two catalysts were characterized by XPS, SEM-EDX, ICP-OES, XRD, HR-TEM and DR-UV-vis. In terms of the photocatalytic reaction, Au–Pd@C and Au–Pd@HT-PO₄³⁻ exhibited photocatalytic activity and the latter displayed higher selectivity. Under optimized experimental conditions, the conversion rate and selectivity using Au–Pd@HT-PO₄³⁻ as catalyst were 52.8% and 49.6% respectively, due to the synergistically double dehydrogenative oxidation derived from alloy nanoparticles and basic support. Moreover, the catalysts had good recyclability without significant loss of activity after several recycles. Therefore, this catalyst could recurrently realize production of vanillin from vanilla alcohol under mild reaction conditions, including in the atmosphere, at ambient temperature and with no addition of alkali, which is very important for a potential “green” strategy towards clean and cost-efficient production of vanillin.