ZSM-5分子筛孔内外表面酸性调控与催化苯和甲醇烷基化反应机制

催化苯和甲醇烷基化反应合成二甲苯是实现甲醇和苯资源科学综合利用的重要途径。针对分子筛外表面酸性位促使对二甲苯异构化明显降低其选择性的问题，本项目提出调控无模板剂法ZSM-5分子筛成核晶化过程，调节Al在MFI结构中的位置分布而改变分子筛孔道中Al的结构强度，实现分子筛孔道内外的酸性位分布可控的目的。该思想有别于现有通过氧化物改性实现分子筛（有机模板剂法）抑制外表面酸性位的常规方法。研究分子筛孔道内外表面酸性强度和位点分布的调控技术和理论；研究有/无模板剂制备的ZSM-5分子筛催化剂酸中心数量、强度、密度、分布和结晶度以及分子筛的物化性质与催化苯和甲醇烷基化反应的活性和对二甲苯选择性之间的联系，揭示分子筛酸性中心与苯和甲醇烷基化反应之间的影响因素。这些结果有助于更全面的了解ZSM-5分子筛催化苯和甲醇烷基化反应，为开发出具有工业应用前景的苯和甲醇烷基化反应催化剂提供理论依据。

The synthesis of xylene by benzene alkylation with methanol is a fascinating subject. To solve the decline of para-xylene selectivity caused by isomerization reaction on the external acid sites of ZSM-5 zeolite, the nucleation and crystallization of ZSM-5 synthesis in the absence of organic structure-directing agent (OSDA) was proposed, which made the structural strength of the Al atom in molecular sieve channels regulable by adjusting the Al distributions at the 12 inequivalent T sites in the MFI framework, thus internal and external surface acidity distribution of ZSM-5 zeolite controllable. The idea is different from the conventional technique (OSDA)，which modifies zsm-5 with oxidates to to inhibit external acid sites. The internal and external of zeolite acidic sites regulation techniques and theories were investigated. The relationship between acid properties, acid amount and Al distribution of ZSM-5 zeolite prepared with or without OSDA and the acitivity and para-xylene selectivity of catalyze benzene alkylation with methanol was investigated to reveal the effect factors between aicd sites of molecular sieve and the catalytic performance of benzene alkylation with methanol. Our experimental results are helpful in understanding the reaction of benzene alkylation with methanol catalyzed by ZSM-5 zeolite, and the result will provide theoretical and experimental foundations for exploring a more effective catalyst with potential industrial application prospect for the alkylation of benzene and methanol.