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Carbene-like reactivity of methoxy groups in a single crystal SAPO-34 MTO catalyst

机译：单晶SAPO-34 MTO催化剂中甲氧基的碳样反应性

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摘要

Synchrotron FTIR microspectroscopy coupled with mass spectrometric analysis of desorbed products has been used to investigate the initial stages of the methanol to olefins (MTO) reaction in single crystals of SAPO-34. Surface methoxy groups (SMS) are key to initial dimethylether (DME) and subsequent carbon–carbon bond formation. Deprotonation of SMS is the critical first step in direct olefin formation at low temperatures and DME is not involved in the carbon–carbon forming step. Experiments with CD3OH confirm the deprotonation step and show an inverse kinetic isotope effect consistent with irreversible deprotonation. The subsequent formation of alkoxide species, which are the precursors of the olefinic hydrocarbon pool present in working MTO catalysts, is initiated via insertion of surface carbene-like species into adjacent SMS. The observed induction period for this process is determined by the limited mobility of SMS and/or carbene species. Olefins formed from cracking of the alkoxide species then transmit carbon–carbon bond formation through the SAPO-34 by rapid diffusion and reaction with further SMS. Acetyl species seen with methanol at higher temperatures support the insertion of CO into SMS suggested in the literature, but these species do not play a role in direct olefin formation.
机译：与解式产物的质谱分析结合的同步加速器FTIR微光谱镜检查已用于研究SAPO-34单晶中甲醇与烯醇对烯醇（MTO）反应的初始阶段。表面甲氧基（SMS）是初始二甲基（DME）和随后的碳 - 碳键形成的关键。 SMS的去质子化是低温下直接烯烃形成的关键第一步，并且DME不参与碳 - 碳形成步骤。使用CD3OH的实验确认了去质子化步骤，并显示出与不可逆的去质子化一致的反向动力学同位素效应。随后的烷氧化物物种是工作MTO催化剂中存在的烯烃烃池的前体，是通过将表面碳样物种插入相邻的SMS中引发的。该过程的观察到的诱导周期取决于SMS和/或Carbene物种的迁移率有限。由烷氧化物的破裂形成的烯烃，然后通过快速扩散和与进一步的SMS反应通过SAPO-34传递碳 - 碳键形成。甲醇在较高温度下看到的乙酰基物种支持将CO插入文献中建议的SMS中，但是这些物种在直接烯烃形成中不起作用。

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