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The application of mesoporous silica in zeolite synthesis can be summarized into four categories: template, shell layer, silicon source, and functional carrier. These roles collaborate to achieve pore structure multilevelization, activity gradation, and process greenization.
Firstly, when mesoporous silica is used as a hard template, it induces the epitaxial growth of microporous crystals along the mesoporous walls during steam or dry gel conversion. This forms an intra-crystalline mesopore-micropore interconnected structure, which not only retains the acidity of the zeolite but also shortens the diffusion path.
Secondly, in-situ coating of a mesoporous silica shell on the surface of microporous cores constructs core-shell zeolites. The thickness and pore size of the shell can be independently regulated, enabling gradient distribution of acidity and shape-selective diffusion, thereby improving the selectivity of cracking and hydrogenation reactions.
Thirdly, mesoporous silica serves simultaneously as a highly dispersed silicon source and a carrier for titanium sources. Through post-titanium modification and methyl grafting, hydrophobic titanium-silicon zeolites are prepared in one step, with the water resistance of water resistant silica gel further optimizing their performance. These zeolites are used in the green oxidation of olefins, with significantly enhanced activity and catalyst lifespan.
Finally, leveraging the morphological plasticity and easily functionalizable surface of mesoporous silica, it can load nano-metals or enzymes to prepare composite zeolite catalytic-adsorptive materials, realizing the integration of reaction and separation.
