Characterization and catalytic alkylation of hydrothermally dealuminated nanoscale ZSM-5 zeolite catalyst

Abstract

The acidity and pore structure of nanoscale ZSM-5 zeolite catalysts with both alumina and rare earth as binders and treated by pure steam were studied by various techniques, including X-ray diffraction (XRD), Ammonia Temperature Programmed Desorption (NH 3 -TPD), Fourier-transform infrared spectroscopy (FT-IR) of adsorbed pyridine, modified Hammett indicator, 27 Al MAS NMR spectroscopy, low temperature N 2 adsorption and adsorption of hexane and cyclohexane. The catalytic performance of the catalysts was investigated using alkylation of toluene with methanol and ethylbenzene with ethanol as probe reactions. The results indicated that the nanoscale ZSM-5 catalysts treated at temperatures up to 800 °C maintained good crystallinity. Both the amount of the tetrahedrally coordinated framework aluminum and that of the octahedrally coordinated nonframework aluminum decreased; the average pore diameter increased; and the adsorption capacities for normal hexane and cyclohexane declined on the dealuminated nanoscale ZSM-5 catalyst samples. For the catalyst treated at 700 °C, not only the catalytic activity for the alkylation of toluene with methanol was improved, but was the selectivity of para -xylene, although the total acid amount decreased significantly and strong acid sites almost disappeared. The alkylation activity was very low when the hydrothermal treatment temperature was 800 °C. Correspondingly, the activity of the catalysts for the alkylation of ethylbenzene with ethanol decreased with elevated treatment temperatures.