Coating hollow silicalite-1 with TS-1 shell as support of Au: preparation and enhanced catalytic stability for direct propylene epoxidation

Au supported on titanium silicalite-1 molecular sieve (Au/TS-1) is commonly used as the catalyst for the direct propylene epoxidation but the carbon deposition is easy to form which deactivates the catalyst. To address this issue, silicalite-1 molecular sieves with hollow structure (H-S-1) are synthesized through post-processing silicalite-1 molecular sieves (S-1). TS-1/S-1 and TS-1/H-S-1 composites are successfully prepared using S-1 and H-S-1 as the core, respectively. Compared to Au/TS-1, the performances of the superior Au/TS-1/S-1 and Au/TS-1/H-S-1 catalysts decrease more slowly. The underlying cause of their unique stability is investigated through TGA, NH3-TPD, and XPS analysis. Remarkably, the amounts of carbon deposition in Au/TS-1/H-S-1 (2.73 wt%) and Au/TS-1/S-1 (2.88 wt%) are significantly lower than that in Au/TS-1 (6.29 wt%). Moreover, the decrease in silanol groups and the increase in hydrophobicity promote product desorption and enhance PO selectivity. This study presents a promising approach for designing and synthesizing highly efficient Au/TS-1 catalysts.