基于类碳正离子结构的分子筛导向合成与催化性能研究

Development of zeolite based catalysts is traditionally a trial and error screening process from known topology library, which is inefficient, labor intensive and irrational. It is still demanding and challenging to design catalytic reaction orientated zeolitic topology and acidity for specific processes. Recent report demonstrated that for reactions with well-understood catalytic mechanism and kinetics, it is possible to use transition-state mimicking molecules as structure-directing-agent to synthesize zeolites with enhance catalytic properties for a particular reaction. This new strategy opens up the possibility to precisely control topology and Al sitting that facilitates the stabilization of a transition-state carbenium cation through confinement. Henceforth, a reaction and application orientated catalyst design can be achieved via choice of appropriate structure-directing-agents that determines precisely the active sites geometry. Herein, we propose to synthesize zeolites for hydroisomerization of n-heptane and alkene methylation by using structure-directing agents mimicking the cationic reaction intermediates, with the target of promoting catalytic behavior by constructing controlled active sites and local voids. As cationic intermediates are ubiquitous and play critical roles for the many zeolite catalyzed reactions, it is regarded as a proof-of-concept strategy to for general catalyst design. The investigation will start with synthesis of zeolitic materials with carbenium mimicking intermediates, followed by extensive structure characterizations, structure-catalysis relationship exploration, as well as kinetic studies. A general rule on the influence of this new types of structure-directing-agents on topology of zeolitic materials, active sites, catalytic performance and kinetic features will be summarized.

分子筛催化剂的研制往往通过对已知拓扑结构库中的分子筛进行催化性能评价筛选完成。近来研究显示，通过采用与催化反应中过渡态结构类似的分子作为分子筛合成的结构导向剂，可以发现性能更优异的新分子筛。基于此，本申请拟通过采用与庚烷异构化、烯烃烷基化反应中经历的碳正离子相似的分子作为导向剂，探索与碳正离子中间体这一分子筛催化中普遍存在的物种结构类似的分子导向合成分子筛，据此控制分子筛结构和酸中心落位，实现对反应活性位和局部空间结构的精确调控，定向构筑尺寸、限域几何形状适合容纳碳正离子的活性位，以期提高目标反应的催化活性和选择性。研究将以结构导向剂分子合成为出发点，在探索所得到分子筛的结构和催化性能的基础上，进一步提高其传质性能，结合分子筛结构、酸中心落位、酸性表征、动力学验证和扩散研究，阐明类碳正离子作为导向剂对分子筛结构和催化性能的影响规律，为面向反应体系的分子筛催化剂研制提供一条新途径。

本研究基于此前Corma等人提出的以与特定反应中间体、过渡态结构类似的分子作为分子筛合成的结构导向剂(OSDA)，可提高分子筛催化剂对目标反应催化性能的思想，开展了新型结构导向剂合成分子筛、催化性能和多级/短轴结构可控制备研究。采用类中间体新型结构导向剂开展了ZSM-48分子筛的合成探索，可以在Si/Al比30-300范围内对酸性进行调控，制得的富铝ZSM-48分子筛，其在催化正庚烷临氢异构反应中表现出更高的催化活性和异构体选择性。发展了以类过渡态三胺、二胺作为结构导向剂，在水/甲苯两相体系中通过相转移合成磷酸盐分子筛的新方法，所制得的SAPO-31分子筛催化剂在催化异构化反应中具有活性和选择性优势。发展了在无钠体系通过结构导向剂交换诱导重结晶制备短b-轴ZSM-5的新方法，所制得催化剂在DTO催化反应中具有高活性、高烯烃选择性和催化剂寿命优势。此外，针对一维孔道分子筛容易沿着轴向生长、扩散距离长的问题，而直接合成短轴或多级孔一维孔道分子筛困难，将珠磨“破坏”方法与重结晶“构筑”方法相结合，提出了珠磨-制孔剂诱导重结晶法，并基于这一方法合成了多种一维短轴分子筛，在临氢异构反应中提高了其选择性。