Effect of ethanol on the crystallinity and acid sites of MFI zeolite nanosheets

Abstract

A series of MFI zeolite nanosheets were synthesized using hydrothermal method with ammonium surfactant (C_22-6-6) as the zeolite structure-generating agent. The effects of ethanol concentration on the textural properties, crystal morphology and acidic properties of the zeolite samples were studied. The zeolite samples were characterized by X-ray powder diffraction, N₂ adsorption isotherms and scanning electron micrographs of the porous materials. The results showed that the addition of ethanol promoted the crystallization of zeolite, and a large number of crystals grew along the b-axis orientation. Based on NH₃-TPD and pyridine-adsorbed FT-IR results, the increase of crystallinity enhanced the acidic properties of the prepared samples. It was attributed to the fact that more aluminum atoms in the sample with higher crystallinity entered into the zeolites framework structure, and participated in coordination. These aluminum atoms coordinating to the oxygen atoms in the framework created Lewis acid and Brønsted acid sites. The present study indicated that ethanol could function as cosolvent and a secondary template to tailor the textural and acidic properties of MFI nanosheets assemblies primarily guided by C_22-6-6 templates. In addition, the quantification of acid site accessibility demonstrated the improvement of the available acid sites and the bulky molecular diffusion efficiency in the MFI nanosheets zeolite.