Engineering a Coordinatively Unsaturated Au–O–Ti3+ Structure Toward Unprecedented H2 Efficiency for Low-Temperature Propene Epoxidation with H2 and O2
Zhaoning Song,
Hao Yan,
Juncong Yuan,
Hongfei Ma,
Jianlin Cao,
Yongxiang Wang,
Qiang Wang,
Chong Peng,
Feng Deng,
Xiang Feng,
De Chen,
Chaohe Yang,
Yongkang Hu
Affiliations
Zhaoning Song
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China
Hao Yan
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China
Juncong Yuan
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China
Hongfei Ma
Department of Chemical Engineering, Norwegian University of Science and Technology, Trondheim N-7491, Norway
Jianlin Cao
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China
Yongxiang Wang
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
Qiang Wang
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
Chong Peng
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China; Corresponding authors.
Feng Deng
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
Xiang Feng
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China; Corresponding authors.
De Chen
Department of Chemical Engineering, Norwegian University of Science and Technology, Trondheim N-7491, Norway
Chaohe Yang
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China
Yongkang Hu
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China
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 quantitatively 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.
