Liquid Phase Oxidation of Benzyl Alcohol over Pt and Pt-Ni Alloy Supported on TiO2: Using O2 or H2O2 as Oxidant?

Benzyl alcohol can be oxidized selectively to benzaldehyde over platinum-based catalysts using either oxygen (O-2, supplied in the form of synthetic air) or the more powerful hydrogen peroxide (H2O2) as the oxidant. Here we compare these oxidants in the aqueous phase oxidation of benzyl alcohol in a batch reactor at 363.15 K or 393.15 K over monodisperse Pt and Pt-Ni nanostructures synthesized with molybdenum hexacarbonyl (Mo(CO)(6)) as a reductant. The initial catalytic activity of either Pt or a Pt-Ni alloy anchored on titania support (TiO2) is much higher when using H2O2 than when using O-2 (supplied in the form of synthetic air). However, the high initial activity using H2O2 is accompanied by a strong decrease in the activity over Pt. Alloying Pt with Ni results in a reduction in the activity in the benzyl alcohol oxidation when using O-2 but enhances the initial activity when using H2O2. The results are rationalized based on a change in the relative surface concentration of oxygen-containing species upon changing the oxidant or alloying Pt with Ni.