自1998年以来，人们广泛认为Au/Ti基催化剂的Au-O-Ti⁴⁺位点是在相对高温条件下丙烯气相环氧化反应的活性位点，但该类催化剂的H₂有效利用率普遍较低。本工作发现了一种在相对低温条件下丙烯气相环氧化反应的新活性位点Au-O-Ti³⁺。值得注意的是，该活性位点主导反应时，最佳温度可从200 °C显著降低至138 °C，并使催化剂保持前所未有的43.6%的H₂有效利用率、90.7%的环氧丙烷（PO）选择性和超过100 h的稳定性。本工作通过调整处理后S-1晶种中Si-OH和Bu₃NH⁺的量，定量构建了Au-O-Ti³⁺活性位点。并且利用原位紫外-可见光谱（operando UV-vis）技术研究了Ti-OOH反应中间体的动态演化过程，结果表明，在Au-O-Ti³⁺活性位点上的Ti-OOH的生成速率比在Au-O-Ti⁴⁺活性位点上的明显增高。此外，氨程序升温脱附（NH₃-TPD）和X射线光电子能谱（XPS）表征以及密度泛函数理论（DFT）计算表明，在相对低温条件下，Au-O-Ti³⁺活性位点中配位不饱和Ti³⁺位点促进了Au和Ti³⁺之间的电子转移，从而增强了催化剂对O₂的吸附能力，有效促进H₂O₂的原位生成，并进一步促进活性中间体Ti-OOH的形成。本工作所报道的结果为强化丙烯直接气相环氧化反应的H₂有效利用率提供了新的思路，而且为推进低温下丙烯直接气相环氧化反应的工业化开辟了新的机会。

Since 1998, the Au–O–Ti⁴⁺ sites of Au/Ti-based catalysts have been widely accepted as the active sites for propene epoxidation with H₂ and O₂ at a relatively high temperature, although they are limited by poor H₂ efficiency. Herein, we demonstrate a novel Au–O–Ti³⁺ active site aiming at low-temperature propene epoxidation. Notably, this active site results in a sharp shift in the optimum temperature, from 200 to 138 °C, and allows the catalyst to maintain an unprecedented H₂ efficiency of 43.6%, a high propylene oxide (PO) selectivity of 90.7%, and a stability of over 100 h. The Au–O–coordinatively unsaturated Ti³⁺ active site is quantitively constructed by tuning the amount of Si–OH and Bu₃NH⁺ in post-treated silicalite-1 seeds. Through operando ultraviolet–visible (UV–vis) spectroscopy, the dynamic evolution of the Ti–OOH intermediate was investigated. It was found that the Ti–OOH generation rate is higher on Au–O–Ti³⁺ than on conventional Au–O–Ti⁴⁺ sites. Moreover, ammonia temperature-programmed desorption (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS) characterizations, together with density-functional theory (DFT) calculations, demonstrated that the coordinatively unsaturated Ti³⁺ sites promote electron transfer between Au and Ti³⁺, thereby enhancing the O₂ adsorption ability of the catalyst and promoting the in situ formation of H₂O₂ and the Ti–OOH intermediate, even at a low temperature. The insights and methodology reported here not only shed new light on maximizing H₂ efficiency over a coordinatively unsaturated Ti³⁺ structure of titanium silicate-1 but also open up new opportunities for industrial direct gas-phase propene epoxidation in a low temperature range.