Enhanced catalytic performance in CH3Br conversion to benzene, toluene, and xylene over steamed HZSM-5 zeolites

Abstract

Catalytic conversion of CH₃Br to benzene, toluene and xylene (BTX) was investigated over HZSM-5 and steam-treated HZSM-5 zeolites. The zeolite samples were characterized by XRD, N₂ physisorption, NH₃-TPD and Py-IR techniques. The results show that due to dealumination as a result of high-temperature steam treatment, there is a decrease of total amount of acid sites, a decline of acid strength, and a lower ratio of Brønsted and Lewis acid sites (B/L). Furthermore, the treatment results in the generation of a secondary pore structure. Overall, there is improved selectivity to BTX and significant enhancement of the performance stability. HZSM-5 steamed at 600 °C (Z-600) shows the best performance (an aromatics yield of about 27% and a lifetime of over 50 h). The improved stability is attributed to the reduced acidity and the newly created mesopores, and the enhanced BTX yield is related to the synergism between the moderate Brønsted acid sites and Lewis acid sites.