Abstract
To improve the catalytic performance of zeolite catalysts in reactions involving bulky molecules, a series of mesoporous Beta zeolite were prepared using organic functionalized fumed silica as the silicon source, which were thoroughly characterized in terms of porosity and acidity. The peaks in X-ray diffraction (XRD) patterns showed broadening, and the external surface area and mesoporosity increased progressively when the content of organic functionalization increased. An infrared (IR) spectroscopy study of adsorbed probe molecules, including pyridine (Py-IR), 2,6-ditertbutylpyridine (DTBPy-IR) and pivalonitrile (Pn-IR), showed that the improvement of mesoporosity increased the accessibility of acidic sites. In the catalytic benzylation of naphthalene with benzyl chloride (BC) over the mesoporous Beta zeolite catalysts, the conversion of BC was significantly increased when the accessibility of Brönsted acid sites improved. The increase of mesoporosity not only improved the diffusion ability of the reactants and products, but also increased the accessibility of acid sites, which greatly enhanced the activity of the mesoporous Beta zeolite catalysts. It is highlighted that the interdependence of mesoporosity, acid type, acid concentration, and strength of the mesoporous Beta zeolites on the catalytic performance in the benzylation of naphthalene with BC was comprehensively studied.
Highlights
Beta zeolite is a microporous crystalline aluminosilicate with a three-dimensional pore system, whose intersecting channels are formed by 12-membered rings with a diameter of 0.67 nm
The present work studied the catalytic benzylation of naphthalene with benzyl chloride (BC) over mesoporous Beta zeolite catalysts that were synthesized using organic modified silica as the silicon source
TL is the low temperature of the desorption of NH3; b TM is the medium temperature of the desorption of NH3; c TH is the high temperature of the desorption of NH3; d ATL is the relative concentration of acid sites determined at TL; e ATM is the relative concentration of acid sites determined at TM; f ATH is the relative concentration of acid sites determined at TH
Summary
Beta zeolite is a microporous crystalline aluminosilicate with a three-dimensional pore system, whose intersecting channels are formed by 12-membered rings with a diameter of 0.67 nm. Catalysts 2018, 8, 504 preformed solids [10,11,12,13] Among these approaches, applying organic functionalized silica as the silicon source in the synthesis system of zeolites has been proved to be an effective and practical method making mesoporous zeolites, and the resulted mesoporous zeolites presented enhanced catalytic performance [14,15,16]. The previous work from our group demonstrated the dramatically improved mesoporosity of a Beta zeolite synthesized by using organic functionalized silica as the silicon source, which showed significantly improved activity in the catalytic reaction for bulky molecules involved in biodiesel production [17]. The present work studied the catalytic benzylation of naphthalene with benzyl chloride (BC) over mesoporous Beta zeolite catalysts that were synthesized using organic modified silica as the silicon source. The porosity and acidity were thoroughly characterized and their effect on the catalytic activity in the reaction was investigated comprehensively
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