| Propylene epoxide (PO), as a versatile bulk chemical intermediate, is widely used in the production of a variety of derivatives. Direct propene epoxidation with molecular H2 and O2 to synthesize PO is a greener, simpler and more sustainable route compared with traditional chlorohydrin and several organic hydroperoxide processes. In this reaction system, uncalcined TS-1 with blocked micropores (TS-1-B) supported Au catalyst (Au/TS-1-B) shows a high stability. But for industrial application, it needs a further improvement.Titanium silicate-1 with blocked pores (TS-1-B) supported Au-Ag catalysts were prepared by sequential deposition-precipitation method followed by in-situ reduction, and tested for direct propene epoxidation with H2 and O2. Then Au/TS-1-B, Au-Ag/TS-1-B and Ag/TS-1-B catalysts were tested. Characterizations such as HAADF-STEM, UV-vis DRS and FT-IR were used to investigate the influence of Ag on Au-based/TS-1-B. Ag/TS-1-B was shown to be almost inactive for the formation of propene oxide (PO). In contrast, introduction of Ag into Au-based/TS-1-B gave rise to the PO formation rate, which was most likely due to the enhanced dispersion of Au nanoparticles and the formation of Au-Ag alloy. Furthermore, effects of Au/Ag molar ratio were investigated. The bimetallic catalyst with Au/Ag molar ratio of 10:1 showed the highest stable PO formation rate. A comparison of the stable PO formation rates between our developed catalyst and other reported Au/Ti-containing catalysts was carried out, and then the plausible catalyst structure and activity relationship was provided.Finally after introducing Ag, the stability of catalyst was improved due to the decrease of coke formed on Au-Ag/TS-1-B and the percentage of low-molecular polyolefine. All this accounts for the significantly improved activity and stability by introduction of Ag. The insights revealed here could guide rational design of Au-based/Ti-containing catalysts for propene epoxidation with H2 and O2. |
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