Hierarchical architectures of ZSM-5 nanocrystalline aggregates with particular catalysis for lager molecule reaction

Abstract

The spherical self-assemblies of ZSM-5 nanocrystals were hydrothermally synthesized by using organo-functionalized mesoporous silica (MS) as silica source. The prepared materials were well characterized by XRD, FTIR of framework vibration, SEM, TEM, N2 adsorption/desorption and TG analyses, to reveal their hierarchical architectures. The ZSM-5 nano-aggregates are composed of size-tunable nanocrystals, and the size and different morphologies of nanocrystals changed significantly from silanized MS rather than unsilanized MS. Spontaneously stacking of nanocrystals in the zeolitic crystallization based on degrees of silanization on MS surface results in the ZSM-5 samples have high external surface area and mesopore volume from intercrystalline among the nanoparticles. The evaluations of NH3-TPD, pyridine- and 2,6-ditertbutylpyridine-adsorbed FTIR as well as catalytic performances in benzylation reaction of 1,3,5-trimethylbenzene for the ZSM-5 zeolitic samples display the accessibility of acid sites and the catalytic activities for the synthesized hierarchical ZSM-5 zeolites are remarkably enhanced. It is clear that the results can be ascribed to the advantages of hierarchical ZSM-5 zeolites for the catalytic conversion of larger molecule, because of the reduction of the steric limitations and faster diffusion of the reaction species.