Does the Presence of ZSM-5 Influence the Catalytic Activity of Mesoporous Molecular Sieves?

摘要

Hierarchical zeolites have emerged as an important class of materials leading to improved catalytic performance compared to their microporous parents due to shortened micropore diffusion path length as a result of a secondary mesopore network of inter- or intra crystalline nature [1]. Corma et al. [2] reported a post-synthesis dealumination process via steaming or acid leaching on full-grown zeolites. Perez-Ramirez et al.[3] investigated the synthesis of mesoporous ZSM-5 by controlled silicon leaching with NaOH, which was reported to display much improved catalytic performances as compared with their microporous counterpart. Catalytic and spectroscopic study of the dealuminated commercial beta zeolite has also been reported in the literature [4]. In general, several synthesis strategies have been developed to obtain materials which combine the advantages of mesoporous materials and those of zeolites in terms of stability and acidity to improve the conversion and selectivity. The significant progress toward the zeolitisation of mesoporous aluminosilicates was pioneered by the van Bekkum group via partially recrystallizing mesoporous framework walls into nanosized ZSM-5 zeolite [5]. The high catalytic activity of an unusual zeolite-coated mesoporous aluminosilicates was attributed to the nanocrystalline zeolitic nature of their pore wall surface [6]. Also, synthesis of a highly stable mesoporous molecular sieves with structure analogous to MCM-48 but with zeolite secondary building units is among the micro-mesoporous materials recendy reported in the literature.