Insights into size-dependent activity and active sites of Au nanoparticles supported on TS-1 for propene epoxidation with H_2 and O_2

摘要

Propene epoxidation with H_2/O_2 is a typical structure-sensitive reaction. For a given support containing tetra-coordinated Ti species such as TS-1, the catalytic activity is greatly influenced by supported Au nanoparticle size. The identification of size-dependent activity of Au catalyst was achieved over a series of Au nanoparticles (2.6–5.1 nm) deposited on the exterior surface of TS-1 by employing uncalcined TS-1. Through this approach, we could obtain very stable Au catalysts with distinguishable and uniform-sized Au particles, which are critical for structure-sensitivity analysis. The PO formation rate (mol_(PO) s~(-1) mol_(Au)~(-1)) over these catalysts was found to vary with average Au diameter (d) as d~(-2.7±0.3). Moreover, typical Au nanoparticles on uncalcined TS-1 appeared as truncated cuboctahedron with top facet of (111). Model calculations derived from the representative Au particle shape and the above size-dependent activity were then performed to show that corner sites of Au nanoparticles are dominant Au active sites for propene epoxidation.