Synthesis New Hierarchical Zeolites By Confined Space Growth Method

Hierarchical zeolites have ordered microporosity,high crystallinity and strong acidity inherited from their zeolitic frameworks and intracrystalline meso-/macro porosity,which can effectively reduce the mass transfer resistance and further promote hierarchical zeolites to be ideal catalysts and adsorbents used in certain process with bulky molecules involved.As one of the most important synthesis methods,the confined space synthesis holds exciting implications for tailoring the framework structure,mesoporosity(size and shape),morphology and composition of hierarchical zeolites with precisions unattainable by the other approach.However,the nucleation and growth process of zeolites and other silicon porous materials within the inert matrix of hard templates are still unclear.In this work,a series of attempts to fabricate hierarchical porous materials have been achieved by confined space synthesis,assisted with steam-assisted crystallization(SAC),hydrothermal treatment(HT),seeded growth and overgrown methods,followed by the acquirement of three kinds of hierarchical porous materials with unique structures and morphologies.(1)Mesoporous silica nanoparticles with a three dimensionally ordered close-packing structure(3DOc-p MSNs)were confined synthesis within three dimensionally ordered mesoporous carbon(3DOm carbon),and the obtained 3DOc-p MSNs presented an uniform mesoporous silica spherical particles with a controllable particle size ranged from 10 to 160 nm and various mesopore morphologies of hollow,multicellar,disordered wormLike,and ordered structure with the increasing of the confined space provided by the 3DOm carbon.Moreover,sonication induced fragmentation of 10,20,and 40 nm 3DOc-p MSNs resulted in a clear suspension of highly monodispersed mesoporous silica nanoparticles with the corresponding particle size and mesopore structure.(2)BEA/MFI zeolite nanocomposites were confined synthesis through two kinds of strategies.By alternant hydrothermal treatments,BEA and MFI zeolites were confined synthesis within 3DOm carbon tempaltes in succession,and the obtained products revealed a composite structure of two kinds of zeolites(BEA and MFI)in single particle and the morphology of replicated 3DOm-i structure.Another strategy was based on overgrown method,and a composite of BEA and MFI zeolites were obtained by overgrown of MFI crystals on the 3DOm-i BEA particles by steam-assisted crystallization(SAC).(3)Hierarchical SAPO-34 zeolites with a three dimensionally ordered mesoporous-imprinted structure(3DOm-i SAPO-34)were confined synthesis within 3DOm carbon by multiple hydrothermal treatments,and the size of the spherical elements controlled from 10 to 80nm.The catalytic performance of the obtained 3DOm-i SAPO-34 was evaluated by the methanol-to-olefin(MTO)reaction,and the results indicated that the 3DOm-i SAPO-34 had a better lifetime in MTO reaction than the conventional bulky SAPO-34 zeolite by reason of the improvement in mass transfer resistance.