甲烷芳构化反应的高效多功能催化剂纳米尺度设计与制备

Methane conversion is of great significance for the utilization of natural gas. Mo/ZSM-5 is one of the best catalysts for the reaction of methane non-oxidative aromatization, in which methane can be converted to aromatics and hydrogen in one single step. However, the rapid deactivation of catalyst together with the low single-pass conversion of methane greatly hamper the commercialization of the process. Therefore, to develop highly efficient and stable catalysts is on the top of the list of consideration. This project will systematically study the effect of each parameter of the catalyst, such as crystal domain size and Si/Al ratio, on the catalytic activity, product selectivities and coke formation using three dimensionally ordered mesoporous-imprinted (3DOm-i) ZSM-5 as the model catalyst. The reason of using 3DOm-i ZSM-5 is that the crystal domain size and Si/Al ratio can be easily tuned in the case of the other ones are fixed, with the aids of the hard template synthetic strategy. Under the guidance of the systematic study, a highly active and coke-resistant Mo/ZSM-5 catalyst will be designed and further be prepared. Based on the deeper understanding of the reaction, one step forward will be made by proposing a concept of multifunctional catalyst by assembly of different functional modules. Proof of concept trials will be conducted.

甲烷转化对天然气资源的利用具有重要意义。Mo/ZSM-5是甲烷无氧芳构化反应的有效催化剂，可以一步直接将甲烷转化为高价值的芳烃和氢气，然而催化剂的快速失活和低转化率限制了其商业化。研发高效、高稳定性的催化剂是当前急需解决的问题。本项目将以三维有序介孔复刻(3DOm-i) ZSM-5分子筛作为催化剂模型，利用其尺寸可控的球形晶粒在纳米尺度上规则有序排列的结构特点，通过精准独立地调变晶粒尺寸和酸位密度，排除各参数之间的相互影响，系统研究催化剂各参数对反应活性、产物选择性以及积碳的影响。在总结规律的指导下，设计并制备用于甲烷转化的高效、稳定的催化剂。在此基础上进一步提出以目标功能为导向的模块化组装多功能催化剂的概念，并进行合成尝试。

沸石催化剂的晶粒尺寸和酸点的性质既影响催化剂的活性和选择性，也影响积碳的产生和催化剂的失活，需要精细调变。然而在沸石催化剂制备过程中晶粒尺寸以及酸性质往往很难分别单独调变，因此难以在排除一个因素的情况下研究另一个因素对催化性能的影响。本项目旨在通过建立参数精确可调的催化剂模型体系来系统研究沸石催化剂的扩散长度和酸点的性质分别单独对催化剂性能的影响，深入理解反应机理和催化剂失活机理，总结规律，最后得到理想催化剂各项指标，从而指导催化剂的设计合成。我们提出一种具有蛋白石结构的沸石催化剂，其微球的尺寸可在30~600 nm范围内精确调变并且沸石的硅铝比也可单独调变，从而可以在催化反应测试中单独研究一种因素对催化剂性能的影响规律。通过将硬模板法与蒸汽辅助结晶法（SAC）相结合，我们成功地制备了几个系列具有不同粒径与硅铝比的ZSM-5沸石与SSZ-13沸石。催化测试结果验证了这种具有蛋白石结构的沸石催化剂可以作为一个模型体系来获得催化剂参数与性能的关系，成功获得催化剂的最佳参数。本项目建立的催化剂模型体系可以作为一个通用的评价方法，从需求出发指导沸石催化沸石催化剂的优化与设计合成。