Tailored mesoporosity and acidity of shape-selective fibrous silica beta zeolite for enhanced toluene co-reaction with methanol

Abstract

Fibrous silica beta zeolite (FSB) catalysts, which are excellent catalytic materials for petrochemical processes, were prepared by a microemulsion system assisted by commercial beta zeolite (BEA) seed crystallization under different urea/tetraethyl orthosilicate (urea/TEOS) ratios, denoted as 0.5:1-FSB, 1:1-FSB and 1:0.5-FSB. The physicochemical properties of the catalysts were investigated by XRD, MP-AES, FESEM, TEM, N2 physisorption and FTIR. The characterization results revealed that the dendrimeric silica fibers surrounding the BEA core shell of FSB were improved when the urea/TEOS ratio was altered, particularly for the ratio of 1:1. The highest terminal silanol and silanol nest intensities further confirmed its highest density of dendrimeric fibers. The catalytic testing of toluene methylation at 673 K resulted in the following order of p-, o- and m-xylene production ratio: 1:1-FSB (6/2/0) > 0.5:1-FSB (6/4/4) > 1:0.5-FSB (2/1/1). The catalyst with denser dendrimeric fibers led to lower acidity and pore volumes, which assist in selectively producing p-xylene and limiting the formation of side products. The FSB with denser dendrimeric fibers was also found to have a slower internal mass transfer rate, which is directly proportional to the activation energy. Optimization by the response surface methodology showed that the reactant molar ratio and reaction temperature were significant factors in the toluene methylation. The remarkable performance of these catalysts in the toluene co-reaction with methanol highlights their potential as future catalysts in the industrial application of toluene methylation and other chemical processes.