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钛硅分子筛-1双核位点实现高效环氧化反应
作者:小柯机器人 发布时间:2020/11/2 16:36:17

钛硅分子筛-1(TS-1)的高效环氧化是由于双核钛位点的存在,这一成果由苏黎世理工的Christophe Copret研究组经过不懈努力而取得。 相关论文于2020年10月28日发表在《自然》杂志上。

研究人员结合光谱和显微镜,详细描述了一系列的高活性和选择性的具有分散钛原子的TS-1丙烯环氧化催化剂。研究人员发现,与H217O2接触时,所有样品均表现出特征性的固态17O核磁共振特征,这表明在双核钛位点上形成桥接过氧物质。此外,密度泛函理论计算表明,两个钛原子之间的协同作用使丙烯能够通过低能反应途径进行环氧化,其关键的氧转移过渡态类似于过酸对烯烃的环氧化。因此该研究团队提出双核的钛位点,而不是孤立的钛原子在框架中,解释TS-1与过氧化氢进行丙烯环氧化的高效率。

更新后的活性位点结构观点可能实现对TS-1的进一步优化和工业环氧化过程。光谱学、显微镜和理论计算共同表明,钛硅分子筛-1作为环氧化催化剂的活性是由于双核钛位点的存在。

据了解,钛硅分子筛-1(TS-1)是一个具有MFI框架结构的沸石材料,其中1 - 2%的硅原子被钛原子替代。由于它具有用过氧化氢(H2O2)催化环氧化烯烃的能力,并只产生水为副产物,因此它在工业中被广泛采用。每年约一百万吨环氧丙烷以该方式生产。TS-1的催化性能通常归因于在沸石框架中孤立存在的Ti(IV)位点。然而,尽管已经有四十年的实验和理论研究,由于全面表征TS-1充满挑战,这些Ti(IV)位点的结构还未得到确认。

附:英文原文

Title: Efficient epoxidation over dinuclear sites in titanium silicalite-1

Author: Christopher P. Gordon, Hauke Engler, Amadeus Samuel Tragl, Milivoj Plodinec, Thomas Lunkenbein, Albrecht Berkessel, Joaquim Henrique Teles, Andrei-Nicolae Parvulescu, Christophe Copret

Issue&Volume: 2020-10-28

Abstract: Titanium silicalite-1 (TS-1) is a zeolitic material with MFI framework structure, in which 1 to 2 per cent of the silicon atoms are substituted for titanium atoms. It is widely used in industry owing to its ability to catalytically epoxidize olefins with hydrogen peroxide (H2O2), leaving only water as a byproduct; around one million tonnes of propylene oxide are produced each year using this process. The catalytic properties of TS-1 are generally attributed to the presence of isolated Ti(IV) sites within the zeolite framework. However, despite almost 40 years of experimental and computational investigation, the structure of these active Ti(iv) sites is unconfirmed, owing to the challenges of fully characterizing TS-1. Here, using a combination of spectroscopy and microscopy, we characterize in detail a series of highly active and selective TS-1 propylene epoxidation catalysts with well dispersed titanium atoms. We find that, on contact with H217O2, all samples exhibit a characteristic solid-state 17O nuclear magnetic resonance signature that is indicative of the formation of bridging peroxo species on dinuclear titanium sites. Further, density functional theory calculations indicate that cooperativity between two titanium atoms enables propylene epoxidation via a low-energy reaction pathway with a key oxygen-transfer transition state similar to that of olefin epoxidation by peracids. We therefore propose that dinuclear titanium sites, rather than isolated titanium atoms in the framework, explain the high efficiency of TS-1 in propylene epoxidation with H2O2. This revised view of the active-site structure may enable further optimization of TS-1 and the industrial epoxidation process. A combination of spectroscopy, microscopy and theoretical calculations shows that the reactivity of titanium silicalite-1 as an epoxidation catalyst is due to the presence of dinuclear titanium sites.

DOI: 10.1038/s41586-020-2826-3

Source: https://www.nature.com/articles/s41586-020-2826-3

期刊信息
Nature:《自然》,创刊于1869年。隶属于施普林格·自然出版集团,最新IF:42.778
官方网址:http://www.nature.com/