分子筛催化甲醇转化反应中碳正离子的产生及作用机制的实验和理论研究

Methanol to olefins (MTO) conversion over zeolites is an important reaction with promising application. The reaction system is complicated and proved to be unique in mechanism involving hydrocarbon pool and related carbenium ions. The key aspect for understanding reaction mechanism is to study the formation and transformation of the carbenium ions. However, only a few types of carbenium ions were observed under special conditions. Based on the great progress in our previous study, multi in situ techniques, such as in situ NMR, in situ FT-IR, and in situ UV-Vis, will be employed in the detection and structure confirmation of the carbenium ions generated in the MTO reaction. In combination with the isotopic labeling technique and theoretical calculation methods, the correlations between the carbenium ions and reactant/product will be established, and the influences of the micro-environment of zeolites channels or cages on the structure and reactivity of carbenium ions as well as the reaction pathway will be investigated. These results will be used to elucidate the detailed reaction steps of methanol-to-olefins transformation via the carbenium ion intermediates and to clarify the role of confinement effects of the catalyst in the MTO reaction.

分子筛催化甲醇制烯烃（MTO）反应具有重大的应用背景，但反应体系十分复杂。以碳池为基础的涉及碳正离子的反应机理显示出了该反应的特殊性。对碳正离子及其作用的研究是探究反应机理的关键。但是目前仅有少数种类的碳正离子在特殊条件下被观测到。本申请在前期进展的基础上，拟利用原位表征技术（原位固体核磁、原位红外、原位紫外光谱等）结合同位素标记、理论计算等方法对MTO反应中可能涉及的碳正离子进行结构确认和监测，并关联反应物和产物，研究分子筛孔道或超笼的微环境对碳正离子的结构、活性以及反应历程的影响，阐明甲醇分子在分子筛的孔道或超笼内通过碳正离子活性中心转化成烯烃产物的反应机理及分子筛的限阈效应在甲醇转化反应中的作用。

分子筛催化甲醇制烯烃（MTO）反应具有重大应用背景，理解该反应进行的机理和产物选择性控制原理具有重要的理论和现实意义。本项目采用多种原位表征技术结合同位素标记、理论计算等方法对该复杂反应体系中涉及的碳正离子进行捕获和观测，并与反应历程进行有机关联，进而对比研究了分子筛孔道/超笼的微环境对反应中间体结构、活性以及产物分布的调控作用。通过系统研究，在8元环、10元环、12元环孔口的多种分子筛（SAPO-35, SAPO-34，SAPO-18，DNL-6，ZSM-22, ZSM-35，ZSM-5，H-Beta，MCM-22，MOR等）上实现了真实MTO反应体系中碳正离子的原位观测，并结合其它实验事实提出了甲醇通过碳正离子转化为烯烃产物的反应机理，进而通过DFT计算对机理进行了理论验证。在此基础上，证实了分子筛孔道/超笼通过控制反应中间体（如碳正离子等）的种类和活性，进而调控MTO反应产物选择性的催化机制。相关结果为调控MTO产物分布和开发新的催化剂提供了理论支撑。