Silica-Confined Pt 3 Sn Clusters for Propane Dehydrogenation

Silica-confined Pt x Sn 1– x ( x = 0.6–1.0) clusters were examined for the dehydrogenation of propane to propylene, in terms of the activity and selectivity. It was found that the Pt 0.8 Sn 0.2 cluster of 1.5 nm, encapsulated in a porous silica particle of about 20 nm, was highly active and selective, yielding propane conversion of 20% and propylene selectivity of 97% at 873 K. The specific activity, based on Pt mass, was approximately two times greater than that over the Pt cluster at a similar size. The Pt 3 Sn alloy in a face-centered cubic structure served as the active phase, in which Pt and Sn atoms catalyzed synergistically. The Pt atoms dominated the activity, while the Sn atoms controlled the selectivity by blocking the low-coordinated Pt sites for cracking the C–C bond. Structural analysis on the spent catalysts revealed that both the size and the atomic arrangement of the metal clusters remained unchanged, evidencing that the spatial confinement of porous silica physically restricted the aggregation and sintering of the smaller metal clusters at such a high temperature and under the highly reductive gases. Instead, accumulated cokes were mainly responsible for the deactivation.