Au supported defect free TS-1 for enhanced performance of gas phase propylene epoxidation with H2 and O2

Abstract

The traditional TS-1 zeolite synthesis method inevitably produces extraframework titanium species, which reduces the reaction performance. Optimizing the coordination environments of Ti active sites in TS-1 zeolite is a big challenge. Herein, we report a facile strategy for the synthesis of a high-quality TS-1 zeolite without anatase Ti species via a hydrothermal method using urea as a mineralizer. The coordination environment of the Ti species in TS-1 zeolites was investigated via UV-vis and UV-Raman spectroscopies. The addition of urea changed the crystallization rate of TS-1 so that it matches the insertion rate of titanium and silicon into the framework, thereby avoiding the generation of anatase TiO₂, and also the formation of defects simultaneously. It was found that the Au/TS-1-urea catalyst exhibits excellent performance in the direct gas phase epoxidation of propylene, with PO formation rate increasing to 140.32 g (h kg_cat)⁻¹ from 70.94 g (h kg_cat)⁻¹, almost twice compared with those of conventional Au/TS-1. Various ex and in situ characterization studies evidenced that the excellent activity is attributed to the high dispersion of tetra-coordinated titanium sites and the enhanced hydrophobicity with free defects. This facile synthetic strategy may open up new prospects for the design and synthesis of defect-free TS-1 zeolites and their potential applications in various selective oxidation reactions.