(318e) Size-Selected Pt Nanoparticles Synthesized Via Micelle Encapsulation: Effect of Pretreatment and Oxidation State On the Activity for Methanol Decomposition and Oxidation

This article presents the effect of pretreatment conditions on the oxidation state and subsequent activity for methanol (MeOH) decomposition and oxidation of size-selected, micelle-synthesized, Pt nanoparticles (NPs) supported on nanocrystalline ZrO₂. Exposure to an oxygen-rich atmosphere was observed to be the most effective pretreatment for producing clean, thermally stable, and active NP catalysts from polymeric reverse micelles. The Pt-oxide species formed on our samples upon annealing in O₂ were found to be highly stable, and could not be fully reduced under the reaction conditions. This effect is attributed to a strong Pt/ZrO₂ interaction and the possible stabilization of interfacial Pt-O-Zr species. Nevertheless, the initial presence of Pt-oxide species in our samples was found to have little influence on the conversion or selectivity in MeOH decomposition reactions due to their tendency to reduce (with the exception of interfacial Pt-O-Zr sites) in the presence of MeOH and its decomposition products (i.e. CO). During MeOH oxidation reactions, the oxides of Pt appear to be very stable and as active as metallic Pt. Our inability to reduce these oxidized Pt species in the course of the latter reactions is attributed to their possible participation in Mars-van Krevelen-type processes, in which bound-oxygen (NP shell) may be replenished with oxygen from the gas phase.