The comparison of mesoporous HZSM-5 zeolite catalysts prepared by different mesoporous templates and their catalytic performance in the methanol to aromatics reaction

Abstract

Three kinds of mesoporous HZSM-5 were synthesized successfully by using a hydrothermal methodology with different mesoporous templates, namely, hexadecyl trimethyl ammonium bromide (CTAB), dimethyl distearylammonium chloride (DDAC) and carbon nanotube (CNT). The differences in crystallinity, textural property and acidity among these micro-mesoporous composite molecular sieves were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy techniques, transmission electron microscopy, nitrogen adsorption and NH3 temperature programmed desorption. The catalytic performances of these mesoporous HZSM-5 zeolites were evaluated by methanol to aromatics (MTA) reaction, and the conventional microporous HZSM-5 was also tested in this reaction for comparison. The results show that mesoporous HZSM-5 zeolite synthesized with CNT mesoporous templates exhibited the highest BTX yields and lowest rate of carbon deposition in MTA reaction among all catalysts. This improved catalytic performance is mainly attributed to not only the well-preserved strong acid sites, which would provide enough active sites for methanol aromatization, but also the generated intra-crystalline mesopores, which would facilitate the access of reactant to the active sites and improve the mass transfer of products. However, mesoporous HZSM-5 synthesized with CTAB and DDAC mesoporous templates did not present improved catalytic performances due to their disconnected micro-mesopores and inadequate strong acidic sites.