Abstract Understanding the nature of Au-Ti bifunctional catalysis is important yet challenging for improving direct propylene epoxidation with H2 and O2 to propylene oxide (PO). Herein, we report a facile strategy to fabricate four different crystal sized TS-1 with the presence of highly active isolated Ti4+ species by adjusting the amount of TPAOH template. The resultant uncalcined zeolite samples, i.e., TS-1-B, are employed to load Au via deposition–precipitation with urea for obtaining similar sized Au immobilized on TS-1-B catalysts and thus excluding the size effects of Au active sites. The zeolite crystal size effects are further probed, and then decreasing the crystal size gives rise to the simultaneous promotion in PO formation rate and selectivity, as well as H2 efficiency. These are attributed to the Au-Ti electronic synergy based on UV–vis and XPS measurements. The insights reported here could benefit the development of high-efficiency Au-Ti bifunctional catalysts for this reaction.

中文翻译：

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Au/未煅烧TS-1双功能催化剂对丙烯与H2和O2直接环氧化反应的沸石晶体尺寸影响

摘要 了解 Au-Ti 双功能催化的性质对于改善丙烯与 H2 和 O2 的直接环氧化反应生成环氧丙烷 (PO) 很重要，但也具有挑战性。在此，我们报告了一种通过调整 TPAOH 模板量来制造四种不同晶体尺寸的 TS-1 的简便策略，其中存在高活性分离的 Ti4+ 物种。得到的未煅烧沸石样品，即 TS-1-B，用于通过沉积-沉淀用尿素负载 Au，以获得固定在 TS-1-B 催化剂上的类似尺寸的 Au，因此排除了 Au 活性位点的尺寸效应。进一步探讨了沸石晶体尺寸效应，然后减小晶体尺寸可同时提高 PO 形成速率和选择性，以及 H2 效率。这些归因于基于 UV-vis 和 XPS 测量的 Au-Ti 电子协同作用。这里报告的见解可能有利于开发用于该反应的高效 Au-Ti 双功能催化剂。