基于微观铝分布调控构建金属/ZSM-5分子筛双功能催化剂及其催化转化轻质正构烷烃研究

Light normal alkanes (C6-C8) are widely existed in reformate raffinate. Because of the low octane number and high stability, the optimizing utilization of them needs to be solved urgently. In this project, highly effective metal/ZSM-5 bifunctional catalysts will be constructed for the conversion of light normal alkanes into valuable light olefins and aromatics. Given the situation that the present bifunctional catalysts suffer from the unmatching of dehydrogenation of metal sites and the acid properties of zeolites as well as the discoordination between diffusion and bifunctionality, leading to the difficulty in achieving the high selectivity to target products and good stability simultaneously,a post-treatment strategy to regulate the local framework negative charge density by modulating the microscopic Al distribution of zeolite is proposed, and the dehydrogenation active sites of metal species could be introduced onto zeolite on this basis. For the pre-protection of Al pair, the introducing of dehydrogenation metal ions before the post-treatment would be also studied, and together with that, metal/ZSM-5 bifunctional catalysts would be prepared as a whole. By investigating the as-introduced different metal species and their chemical states, the regulation mechanism of the effect of Al distribution of zeolite on the microscopic acid property and the chemical states of the introduced species will be elucidated. Such a strategy will be further extended to hierarchical ZSM-5 zeolites, and the relationship between hierarchical porosity and bifunctionality of the catalysts as well as the catalytic mechanism would be investigated. It is expected that the present research will help to promote the study of the microscopic acid property of zeolites and the construction of bifunctional catalysts. Meanwhile, it is also of significant importance for the efficient convesion of light normal alkanes.

轻质正构烷烃（C6-C8）广泛存在于重整抽余油中，其辛烷值低，同时又高度稳定，优化利用亟待解决。本项目致力于构建高效金属/ZSM-5分子筛双功能催化剂，将轻质正构烷烃转化为高附加值低碳烯烃和芳烃。针对目前双功能催化剂中金属位与酸性位不匹配、双功能活性位与传递特性不协调导致目的产物选择性和催化剂稳定性难于同时兼顾的难题，本项目提出后处理调控分子筛微观铝分布来调节其骨架局部负电荷密度，在此基础上引入具有脱氢活性金属物种；并采用脱氢金属离子预保护Al pair，结合后处理整体构建金属/ZSM-5分子筛双功能催化剂。研究分子筛微观铝分布对微观酸性和金属存在状态等调控机制，该方法还将进一步拓展至多级孔ZSM-5体系，探讨催化剂多级孔与双功能特性之间的关系，研究反应机理，深入认识其催化作用本质。本项目实施不仅有助于推动分子筛微观酸性研究和双功能催化剂设计，同时还对轻质正构烷烃高效转化具有重要意义。

轻质正构烷烃高度稳定，其优化利用亟待解决。本项目致力于分子筛微观铝分布调控并构建金属/ZSM-5分子筛双功能催化剂，将轻质烷烃高效转化为高附加值低碳烯烃和芳烃。项目研究了后处理及前合成条件对分子筛微观Al分布的影响，发展了分子筛微观Al分布系列调控策略，进一步基于微观Al分布调控构建了Co基ZSM-5双功能催化剂，并通过灵活的还原氧化气氛后处理，制备了高效Ga/ZSM-5基催化剂。研究发现，通过精细调控后处理pH值、分子筛合成过程中采用醇类分子作为孔道填充剂，可有效调变分子筛中Close Al与Single Al含量，从而实现正丁烷催化裂解反应性能调控，其中，Single Al有利于烯烃产物的生成，Close Al含量提高则会促进反应中芳烃产物的生成。在上述工作的基础上，进一步基于Co离子对分子筛Close Al位点预保护，在高Single Al含量条件下，实现了后处理分子筛的Close Al相对含量提高，其有助于反应中间产物丁烯的生成以及转化，进而促进正丁烷整体转化。在纳米薄层ZSM-5分子筛合成过程中，通过调变杂原子B，利用其与骨架Al原子在交叉孔道T位点的竞争作用，调控了骨架Al原子的分布。项目进一步构筑了Co基ZSM-5双功能催化剂，既保留了高Single Al分子筛的催化裂解性能，又引入了具有脱氢活性的金属Co，进一步增强了催化剂的裂解性能。除Co外，还构建了Ga/ZSM-5双功能催化剂，与新鲜的Ga/ZSM-5相比，氧化还原气氛处理后的Ga物种具有更强的脱氢能力，且与分子筛之间的相互作用更强，更高效的双功能匹配在Ga物种和ZSM-5分子筛之间得以实现。项目获得了分子筛微观Al分布、催化剂双功能匹配等与催化剂性能之间的构效关系，为轻质烷烃催化裂解高效催化剂设计提供了新思路。围绕上述及相关研究，共发表SCI标注论文18篇、申请/授权国家发明专利2项。