Effects of Bimesoporous Structure on Surface Acidity and Catalysis of Microspherical MFI Zeolite

Abstract

Microspherical MFI mesoporous zeolites (MMZ-5) with different mesopore volumes and similar silica-alumina ratios were prepared by the bond-blocking principle and confirmed by physical methods. The zeolite materials with high external surface areas contained inter- and intra-crystalline mesostructures. NH3-TPD and in situ FT-IR spectra techniques were used to characterize the acidic properties of the mesoporous zeolites. The results showed that the Py-Bronsted acid sites of the MMZ-5 samples are very similar to that of the conventional ZSM-5 zeolite, but the latter Py-Lewis acid sites are greatly larger than the former. Further, the concentration of DMPy-Bronsted acid sites in the mesoporous zeolites arrived at 70 μmol/g, namely, the 2,6-dimethylpyridine (DMPy) molecule can probe 97 % of the Py-Bronsted acid sites in the MMZ-5 zeolites. The introduction of the mesoporous structure into the MMZ-5 zeolites increased strongly the accessibility of the more bulky molecules, such as the DTBPy molecules. As expected, HMMZ-5-2 sample as an acid catalyst displayed a high reaction activity and an uniform product selectivity in the benzylation of p-xylene with benzyl chloride. .