杂原子纳米沸石亚雏晶交错生长法构建高结晶度有序介孔材料

The combination of mesoporous and microporous materials can not only break through the channel limit of microporous material, and but also solve the poor hydrothermal stability and activity problem of silicon-based mesoporous materials caused by their hydrophilic amorphous wall, which is one of the recent research hotspots in the material and catalysis. To solve the serious diffusion and substrate scope limitation of heteroatomic zeolite in catalytic oxidation reaction, this project aims at the preparation of high crystalline and ordered mesoporous heteroatom zeolite materials. The project will focus on developing a confined-spaced intergrowth method, and achieving a new heteroatom zeolite material with two-level ordered structures. In detailed, heteroatom nano-zeolite sub-crystallites will be used as building blocks to assemble the ordered mesoporous materials. The crystallinity and size of nano-zeolite sub-crystallites, post-treatment process and thickness of mesoporous wall are well controlled to achieve the intergrowth of nano-zeolite sub-crystallites in confined space, and so to assure the high order of mesopores and high crystallinity of wall in the as-prepared mesoporous heteroatom zeolite materials. Moreover, this ordered mesoporous heteroatom zeolite materials will possess a controllable mesoporous size and wall thickness as well as microporous framework structure and composition. This project will also apply this heteroatom molecular sieve with two-level ordered structures to the catalytic oxidation of cyclic bulky molecules, and achieve the understanding of the relationship between the activity and stability of catalysts and their structures.

微介孔材料的复合既可以突破微孔材料孔道小的限制，又可以解决硅基介孔材料由于受到亲水性无定型孔壁组成限制而造成的水热稳定性和催化活性差的问题，是近年来催化工作者关注的热点之一。本项目针对杂原子沸石在催化低温液相氧化反应中面临的扩散和底物限制问题，提出制备高结晶有序介孔杂原子沸石材料。以杂原子纳米沸石亚雏晶为有序介孔孔壁组装单元，通过控制亚雏晶质量、后处理过程以及孔壁厚度实现纳米沸石亚雏晶受限空间交错生长，同时实现材料的介孔有序性和孔壁的高结晶性，发展制备拓扑结构、孔径厚度、杂原子骨架结构以及组成可调的有序介孔杂原子沸石新方法。同时也将获得具有异相lewis酸活性的新型介孔材料，以过氧化物为氧化剂研究和比较其催化氧化性能，最终形成一套对适合大分子催化氧化的有序介孔沸石催化剂的控制制备及其与催化活性、稳定性之间构效关系等关键科学问题的认识。

具有晶态微孔孔壁的介孔材料由于兼顾微孔的稳定性和介孔的扩散性既可以突破微孔材料孔道小的限制，又可以解决硅基介孔材料由于受到亲水性无定型孔壁组成限制而造成的水热稳定性和催化活性差的问题。本项目通过系统研究纳米沸石合成过程，提出选择纳米沸石成核、生长拐点处的纳米沸石亚雏晶做为有序介孔材料组装单元，并在此基础上发展了一种酸性梯度组装生长方法，在常规的混合模板体系成功地制备了孔壁高度沸石化的有序介孔沸石材料，这种有序介孔沸石材料不仅具有较大的比表面积(∼834 m2/g)和孔容(∼0.64 cm3/g)，而且还兼顾了微孔和介孔两种孔径分布。通过系统研究梯度酸性对于介孔有序性以及孔壁沸石化的影响，最终获得了具有较高水热稳定性和高暴露活性位的新型介孔催化材料，在涉及大分子转化的气相/液相反应中都表现出明显的优势。这一结果通过梯度酸性变化来避免孔壁的大量溶解并实现介孔孔壁的高度沸石化，不仅打破了前人关于混合模板体系微介孔不相容的推测，而且由于整个合成过程无需特殊模板剂的使用，也为其进一步实际应用提供了可能。随着对纳米沸石结晶过程的深度理解，本项目还发展了具有树枝状形貌的多级沸石材料、具有由内而外贯通介孔和具有微-介孔互穿孔道的多级孔沸石材料，这些技术及所得的具有丰富界面和孔道性质的材料无疑为高活性介孔催化剂的设计和制备提供了新思路。