Effect of Core-Shell Support on Au/S-1/TS-1 for Direct Propylene Epoxidation and Design of Catalyst with Higher Activity

Catalysts with core-shell structure are particularly attractive because nanoparticles (NPs) can be protected against sintering by a thin zeolite shell. Titanium silicalite-1 coated with silicalite-1 shell to support nanogold (labeled as Au/S-1/TS-1) is reported to exhibit excellent performance for direct propylene epoxidation. However, owing to the internal diffusion, it is difficult for reactants to access some Au-Ti active sites inside TS-1. To investigate the effect of diffusion, we designed S-1/TS-1 with different S-1 coating thicknesses and found an inverse linear relationship between PO formation rate and the thickness of S-1 coating. Furthermore, Au NPs inside TS-1 nanopores made a major contribution. Inspired by the above conclusion, TS-1 with only one thinner S-1 shell to support Au NPs [labeled as Au/S-1/TS-1(0.26)] was prepared successfully and showed higher PO formation rate of similar to 410 g(PO )h(-1) kg(TS-1)(-1). The results help guide us to design the Au-Ti core-shell catalyst more reasonably.