Preparation of platinum nanocatalysts from mixed-valence precursors: investigation on the size effects of complete oxidation of propene†

The effective oxidation of hydrocarbons (HCs) emitted from internal combustion engines is crucial for mitigating atmospheric pollution and meeting stringent emission regulations. Noble metal catalysts, particularly Pt-based systems, are promising for the oxidation of propene, a common unsaturated HC in automobile exhaust. This study investigates the size-dependent propene oxidation activity of Pt nanoparticles (NPs) on Al₂O₃-based supports. We synthesized Pt NPs of specific sizes but with different dispersed states using mixed-valence chlorine-free precursors and further deposited them onto Al₂O₃-based supports. By employing electron microscopy, X-ray absorption spectroscopy, and in situ infrared spectroscopy, we found that as the Pt NP size decreases within the 4–15 nm range, the number of exposed Pt atoms on the surface increases, leading to the higher average valence state of Pt. This enhancement facilitates the cleavage of the C–H bonds in the methyl group of propene, which is the rate-limiting step, thereby improving oxidation activity. Our findings provide insights into the relationship between Pt NP sizes, electronic properties, reaction pathways, and catalytic activity, which are essential for the design of more efficient and durable oxidation catalysts.