Mesoporous and Al-rich MFI crystals assembled with aligned nanorods in the absence of organic templates

Abstract

Mesoporous zeolites have been paid much attention recently due to their excellent mass transfer and high activity for bulky molecules as well as unique shape selectivity, but their syntheses usually require the presence of organic templates. Here, we report organotemplate-free synthesis of mesoporous and Al-rich MFI zeolite in the presence of the zeolite seeds (MFI-SDS). The MFI-SDS crystals are assembled with rod-like nanocrystals having almost the same aligned direction, confirmed by the sample transmission electron microscopy (TEM). The space between nanocrystals forms the mesoporosity in the sample, supported by N2 sorption isotherms. 27Al MAS NMR spectroscopy and ICP analysis show that the MFI-SDS has abundant tetrahedral Al species in the zeolite framework, giving the Si/Al ratio at 9.5. Catalytic tests in cumene cracking show that the MFI-SDS exhibits higher catalytic activities and longer catalyst life than conventional ZSM-5 zeolites synthesized in the absence (ZSM-5-OTF) or presence of organic template, TPA+ (ZSM-5-TPA). The excellent catalytic performance should be assigned to the combined contribution of the presence of both mesoporosity and rich tetrahedral Al species in the MFI-SDS. These features would be critically important for industrial applications of MFI zeolite catalysts in the future.