SAPO-34分子筛催化甲醇及其衍生物转化初始C-H键活化和C-C键生成及自催化反应机制

As one of the important project of C1 chemistry, Methanol-to-Olefins (MTO) process has been successfully industrialized using shape-selective molecular sieve catalysts since 2010. New catalysts development and process optimization require deep and complete understanding of the reaction mechanism to realize the precise manipulation of the target products generation. In MTO study, the formation of the initial olefins with the first C-C bond has been the most conflictive and challenging topic, which has been too difficult to be settled so far. In the present project, the applicants plan to study the initial methanol conversion during the very early stage of MTO reaction over SAPO-34 catalyst, based on our fundamental study experiences about induction period reaction accumulated in the past. Highly time-resolved techniques for heterogeneous catalysis study, in situ solid state NMR, IR, UV-Vis and Raman spectroscopies will be applied for the determination of the intermediates for the initial activation and conversion of methanol or DME over SAPO catalyst. In combination with the experimental investigations and theoretical calculations, the reaction mechanism of the initial olefins generation with the first C-C bond will be proposed. Furthermore, the formation of carbenium ions, as the important intermediates of hydrocarbon pool mechanism, from the initially-generated olefins during the induction period will be studied, which will give a rational explanation of the source for the hydrocarbon pool species. These efforts will be devoted to connect the direct route of C-C bond formation to the indirect mechanism, and these works will be of great significance for the establishment of the complete autocatalysis of MTO reaction, including the first C-C bond formation, initial olefins transformation, hydrocarbon pool species formation and efficient olefins generation. Furthermore, extending the study of the methanol conversion to the reaction of DME and methyl halides, complete prospects of MTO reaction and the reaction from C1 feedstocks to olefins will be revealed.

作为碳一化学重要的发展方向，甲醇制烯烃已经成功实现工业化。催化剂和反应过程的进一步发展都要求更为深刻地理解反应机理以实现对反应途径和烯烃产物更为精准的调控。在甲醇制烯烃反应和机理研究中，第一个C-C键的生成和初始烃池物种的来源一直是最具争议性和挑战性的问题。本项工作拟通过具有高度时间分辨的原位固体核磁等实验技术考察SAPO-34分子筛催化的MTO反应诱导期的最初始阶段，确定反应物在催化剂表面的活化和转化方式，结合理论模拟，揭示第一个C-C键的生成机理。在此基础上，进一步研究初始烯烃转化为烃池物种的过程，链接甲醇转化初始反应阶段的直接机理和高效反应阶段的间接机理，建立包含第一个C-C键形成、初始烯烃的转化、烃池物种的生成在内的完整的甲醇转化的自催化反应机制。拓展反应物甲醇到二甲醚和卤代甲烷，最终构建分子筛催化MTO反应及C1物种转化制烯烃完整的反应历程。

在本项研究中，开展了甲醇转化初始C-C键形成和完整反应历程的研究。利用催化原位研究技术跟踪了甲醇转化最为初始反应阶段。对这一阶段催化剂上反应物吸附物种（甲醇或二甲醚）、反应中间物种和可能的产物物种进行甄别和结构确认。以此为基础建立了SAPO-34分子筛催化甲醇转化初始C-C键生成的反应途径，并进行理论模拟。通过多种实验技术研究诱导期内初始烯烃生成后的反应阶段，确定由直接机理生成的初始烯烃物种向作为间接机理的反应活性中间体的转化过程，解释自催化反应的引发过程和催化剂上有机物种的作用。