Nanoscale ZSM-5 Zeolite for the Benzylation of Aromatic Hydrocarbons

ZSM-5 zeolite in the form of crystalline nanoclusters was synthesized from seeds functionalized by organosilane and its catalytic performance in the benzylation of aromatic hydrocarbon by benzyl chloride was investigated. The zeolite samples were characterized by X-ray diffraction, N-2 adsorption-desorption, and scanning electron microscopy. The results indicated that they were composed of aggregates of nanocrystals about 20 nm. They had high external surface area that was five times that of conventional ZSM-5. The amounts of acid sites were increased, which was indicated by acidity characterization by the Fourier transform infrared spectroscopy of adsorbed pyridine and temperature-programmed desorption of NH3. moreover, accessibility to the acid sites was improved by reducing the size of crystals to nanoscale. In the benzylation of aromatics by benzyl chloride, nanoscale ZSM-5 showed a much higher activity than conventional ZSM-5 because the diffusional limitation for the large reactant was decreased in the nanoscale ZSM-5 zeolite. The benzyl chloride conversion in the benzylation of toluene was 98% at 363 K for 10 h, which was 3.6 times higher than that over conventional ZSM-5. The apparent rate constant over the nanoscale ZSM-5 zeolite was ca. 13 times larger than that over conventional ZSM-5.