Understanding the mechanism of N coordination on framework Ti of Ti-BEA zeolite and its promoting effect on alkene epoxidation reaction
作者:Xiaohang Liang、Xinxin Peng、Dan Liu、Changjiu Xia、Yibin Luo、Xingtian Shu
DOI:10.1016/j.mcat.2021.111750
日期:2021.7
dissociated from the ammonium salt would chelate with the linear Ti-η1(OOH) species and form a bridged Ti-η2(OOH)-R species, which is more stable, more weaker in epoxide adsorption and acidity as well. Therefore, side reactions and H2O2 decomposition would be suppressed, and both alkene conversion and epoxide selectivity would be promoted simultaneously. On the other hand, the excessive NH3•H2O (NH3/Ti>1) or
摘要 详细研究了铵盐对Ti-BEA沸石环氧化性能的影响。设计了有或没有铵盐的烯烃环氧化、环氧化物副反应和H2O2分解的实验,并采用紫外-可见光谱分析了钛氢过氧化物的结构。结果表明,从铵盐中解离出来的氨(或胺)会与线性 Ti-η1(OOH) 物种螯合,形成桥接 Ti-η2(OOH)-R 物种,在环氧化物中更稳定,更弱吸附和酸度也一样。因此,副反应和 H2O2 分解会被抑制,同时烯烃转化率和环氧化物选择性都会得到提高。另一方面,过量的 NH3•H2O (NH3/Ti> 1) 或 NaOH 与 Ti-η2(OOH)-R 物种键合,生成盐状 Ti-η2(OO)-M+ 物种,导致 Ti 活性中心失活。而对于铵盐,例如 NH4Cl,有限的解离度以及酸性环境有助于 Ti 活性中心保持高活性。总之,这项工作为 Ti-BEA 沸石提供了一种实用的 Ti 活性中心调谐方法,以及对其 Ti-hydroperoxo