Pt/Al2O3 Overcoated with Reactive Metal Oxides and Their Application to Catalytic Oxidation of Propane.

Inverse-structured metal-metal oxide materials-where the oxides are located on top of a different metal-can provide unique chemical properties. Here, a few layers of reactive metal oxides, including In₂O₃, MoO₃, Bi₂O₃, or TiO₂, are overcoated on Al₂O₃-supported Pt nanoparticles using atomic layer deposition (ALD). In contrast to prior work focusing on stabilizing metal surfaces or new mixed-valence nanoparticles, here the goal is to create new reactive surfaces and interfaces. The overcoating altered the Pt nanoparticle accessibility as measured by STEM, CO chemisorption, and CO DRIFTS. The reactivity of the overcoated materials is interrogated with temperature-programmed reduction in H₂, in propane, and in the catalytic reaction of propane with O₂. Strong interactions between In₂O₃ and the Pt nanoparticles are evident from changes in Pt accessibility, In₂O₃ reducibility, and tandem catalytic reactivity. MoO₃ and Bi₂O₃ overcoats also showed significant changes to Pt accessibility and the reducibility of the oxide in H₂; Bi₂O₃ addition led to complete propane combustion. This study establishes ALD methods for reactive oxides on high surface area materials suitable for applications such as heterogeneous catalysis, and it illustrates the wide range of useful physiochemical modifications resulting from the unique oxide-metal interfaces generated.