Au supported defect free TS-1 for enhanced performance of gas phase propylene epoxidation with H-2 and O-2

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.