Fabrication of meso- and microporous MFI zeolites by amphiphilic molecules with biphenol group

Abstract

Abstract We reported a strategy to synthesize MFI zeolites with tunable properties by tailoring organic structure-directing agents (OSDAs) under the hydrothermal conditions. The tailored surfactants were obtained by tuning the structure of Gemini-type Cph-10-6-6 and Bola-type BCph-10-6-6, including alkyl tail chains, ammonium groups and alkyl middle chains. The textural property, morphology and acidity of resulting MFI zeolites were characterized by a complementary combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption isotherms and FTIR spectra of pyridine adsorption. Moreover, the correlation between the OSDAs’ composition and the inorganic precursor in the fabrication of zeolite framework was investigated by DFT calculations in this study. The catalytic performance of the resulting MFI samples was investigated by the alkylation of mesitylene with benzyl alcohol. The results revealed that the OSDAs without ammonium groups only leaded to form the micro-structure of zeolites, but the OSDAs with ammonium groups can induce the formation of micro- and meso-structure simultaneously, regardless the OSDAs ended with or without alkyl tail chains. In addition, the resulting MFI zeolites showed an improved catalytic activity in alkylation of mesitylene with benzyl alcohol due to the enhanced pore accessibility, the acidity (Bronsted/Lewis) controlled the activation of benzyl alcohol, and the ratio of external surface area (Sext/SBET) governed the selectivity of alkylation reaction. As a result, tailoring the structure of OSDAs can pick another strategy to synthesize MFI zeolites with tunable zeolite structure and catalytic performance.