固体核磁共振技术在甲醇制烯烃反应中的应用

Applications of Solid-State Nuclear Magnetic Resonance Spectroscopy in Methanol-to-Olefins Reaction

甲醇制烯烃过程是由非石油路线生成低碳烯烃的重要途径之一.分子筛因具备独特的孔结构和可调变的酸性质,而成为甲醇制烯烃过程的核心催化剂.固体核磁共振(NMR)是鉴定物质结构、阐释催化反应机理的强有力的工具,在甲醇制烯烃的研究中被广泛应用.本文主要总结了近年来利用原位固体NMR、多维多核NMR、脉冲梯度场NMR等固体NMR技术研究甲醇制烯烃反应机理取得的重要进展.原位固体NMR可以在真实反应条件下监测催化反应中反应物、中间体和产物的动态演变过程;多维多核NMR可以在不破坏催化剂结构情况下确定反应中间体结构信息,特别是^(129)Xe NMR可以很灵敏探测反应中催化剂的孔道结构变化;脉冲梯度场NMR可用于测定孔道内分子的扩散系数,阐明分子筛的扩散机制.

Methanol-to-olefins(MTO)is a prevalent industrial process for producing light olefins from the non-petroleum route.Molecular sieves are core catalysts for MTO owing to their unique pore structure and tunable acidity.Solid-state nuclear magnetic resonance(NMR)is a powerful tool to elucidate the structure and interpret the catalytic reaction mechanism of the molecular sieves.In this review,we summarize the major progresses in understanding the MTO reaction mechanism with in-situ solid-state NMR,multi-dimensional and-nuclear NMR,^(129)Xe NMR,and pulsed field gradient NMR(PFG NMR).In-situ solid-state NMR can monitor the dynamic changes of the reactants,intermediates and products under real reaction conditions.Multi-dimensional and multi-nuclear NMR offers rich structural information of the reaction intermediate without having to destroy the catalyst structure.Especially,^(129)Xe NMR is applied to sensitively probe the pore structure of fresh and deactivated catalysts.PFG NMR could determine the diffusion coefficients of molecules in pores,and elucidate the diffusion mechanism of the molecular sieve.