摘要
自1998年以来,人们广泛认为Au/Ti基催化剂的Au-O-Ti^(4+)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H_(2)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-Ti^(3+)。值得注意的是,该活性位点主导反应时,最佳温度可从200℃显著降低至138℃,并使催化剂保持前所未有的43.6%的H_(2)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-Ti^(3+)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-Ti^(3+)活性位点上的Ti-OOH的生成速率比在Au-O-Ti^(4+)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-Ti^(3+)活性位点中配位不饱和Ti^(3+)位点促进了Au和Ti^(3+)之间的电子转移,从而增强了催化剂对O_(2)的吸附能力,有效促进H_(2)O_(2)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H_(2)有效利用率提供了新的思路,而且为低温下丙烯直接气相环氧化反应的工业化推进开辟了新的机会。
Since 1998,the Au-O-Ti^(4+)sites of Au/Ti-based catalysts have been widely accepted as the active sites for propene epoxidation with H_(2)and O_(2)at a relatively high temperature,although they are limited by poor H_(2)efficiency.Herein,we demonstrate a novel Au-O-Ti^(3+)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℃,and allows the catalyst to maintain an unprecedented H_(2)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 Ti^(3+)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-Ti^(3+)than on conventional Au-O-Ti^(4+)sites.Moreover,ammonia temperature-programmed desorption(NH3-TPD)and X-ray photoelectron spectroscopy(XPS)characterizations,together with densityfunctional theory(DFT)calculations,demonstrated that the coordinatively unsaturated Ti^(3+)sites promote electron transfer between Au and Ti^(3+),thereby enhancing the O_(2)adsorption ability of the catalyst and promoting the in situ formation of H_(2)O_(2)and the Ti-OOH intermediate,even at a low temperature.The insights and methodology reported here not only shed new light on maximizing H_(2)efficiency over a coordinatively unsaturated Ti^(3+)structure of titanium silicate-1 but also open up new opportunities for industrial direct gas-phase propene epoxidation in a low temperature range.
作者
宋钊宁
闫昊
袁俊聪
马宏飞
曹建琳
王永祥
王强
彭冲
邓风
冯翔
陈德
杨朝合
胡永康
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(State Key Laboratory of Heavy Oil Processing,China University of Petroleum,Qingdao 266580,China;Department of Chemical Engineering,Norwegian University of Science and Technology,Trondheim N-7491,Norway;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;State Key Laboratory of Fine Chemicals,School of Chemical Engineering,Dalian University of Technology,Dalian 116024,China)
出处
《Engineering》
SCIE
EI
CAS
CSCD
2023年第6期144-156,M0006,共14页
工程（英文）
基金
supported by the National Natural Science Foundation of China(21978325 and 22122807)
Outstanding Youth Fund of the National Natural Science Foundation of China(22122807)
Outstanding Youth Fund of Shandong Provincial Natural Science Foundation(ZR2020YQ17)
Natural Science Foundation of Shandong Province(ZR2020KB006)。
