甲醇转化为烯烃过程的催化机理调控研究

Methanol to olefin conversion is one of the important processes that may have profound impact on economy. In recent years, the mechanism of the MTO process has progressed significantly. At molecule level, the structures of several key organic intermediates have been confirmed experimentally. However, several key issues rmeained to be elucidated, including how initial organic intermediates were formed, the role of methanoxyl groups, how the pore structure of a zeolite can modulate the reaction mechanism of MTO process. In this project, we will focus on the modulation of MTO mechanism. We plan to do so by divide the whole MTO process into several stages by choosing zeoliet with specific pore structures so that certain steps in the MTO process are promoted or inhibited. We plan to use several types of reaction modes and exploit various zeolite and isotope substituted compounds for this study. We also plan to control the contact time of reaction species on the zeolite and use NMR and mass spectroscopy to monitor the extent of the reactions. The outcome of this project will provide solid mechanism background for further develipment of MTO into a mature chemical process.

甲醇制烯烃过程对国民经济有着潜在巨大影响。近年来，国内外对甲醇转化为烯烃反应的机理研究逐渐深化，已经从定性描述性阶段进入分子研究层次，多种关键中间体的化学结构已经得到实验验证。但是关键中间体的形成过程，催化剂孔道结构对反应过程的调控作用，催化剂失活过程中有机中间体的演变等问题仍然没有较明确的解释，不同研究手段往往得到不同的结论。本课题将以甲醇制烯烃过程的催化机理调控为核心，将复杂的甲醇转化过程分解为几个较简单过程分别研究，通过催化剂结构设计和反应器设计来促进或者阻止特定催化步骤的进行，调控催化反应的进程，为精确研究催化机理创造条件。研究中，将结合连续流动反应器，脉冲反应器和釜式反应器等研究系统，选择具有特定孔道结构的分子筛催化剂以及关键位置同位素（碳13，氘）标记的反应物，控制反应物在催化剂上的停留时间，综合运用核磁、质谱等手段开展研究，为进一步发展甲醇转化为烯烃过程的催化机理奠定基础。

近年来，国内外对甲醇转化为烯烃反应的机理研究逐渐深化，已经从定性描述性阶段进入分子层次研究，多种关键中间体的化学结构已经得到试验验证。但是关键中间体的形成过程，催化剂孔道结构对反应过程的调控作用等问题仍然没有较明确的解释，不同研究手段往往得到不同的结论。本项目针对上述问题，以甲醇制烯烃过程的催化机理调控为核心，取得重要结果如下：通过设计一系列的实验，确定了HZSM-22和HZSM-23分子筛上痕量烯烃的来源于外酸位和孔口催化的作用，打破了其他研究者报道的通过在内表面发生的烯烃甲基化裂解机理。