Effects of urea-silica precursor ratio in the synthesis of fibrous silica beta zeolite for toluene methylation

Abstract

Recently, the need to create a versatile toluene methylation catalyst receives a major attention in the production of p-xylene due to its less energy intensive. The current catalyst produced low p-xylene yield due to its strong acidity and large pores. A novel fibrous silica beta zeolite (FSB) was successfully prepared by microemulsion assisted with zeolite-seeds crystallization using different urea-silica ratio. The properties of the catalysts were characterized using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy using potassium bromide method and adsorption of 2,6-lutidine. The results indicate that different urea-silica ratio altered the density and perfection of dendrimeric silica fibres, consequently decreased the acidities, surface area and pore volume of the catalysts. Catalytic performance was conducted at 573 - 723 K under atmospheric pressure with a reactant molar ratio of 1. At 673 K, the p-xylene yield was in the following order: 0.5:1-FSB (23.3%) > 1:1-FSB (23.05%) > 1:0.5-FSB (7.59%) > beta (5.79%). Furthermore, the optimization using response surface methodology for 1:1-FSB catalyst demonstrated the reactant molar ratio and temperature as significant parameters with high coefficient of determination (R2 =0.9159). The Weisz-Prater criterion is in the following order: 1:1-FSB > 1:0.5-FSB > 0.5:1-FSB > beta. The employment of the synthesized catalyst in the toluene methylation revealed a remarkable performance, suggesting its potential as a future catalyst in industrial application of toluene methylation and in other chemical processes.