Dehydro-Aromatizationof N-Hexane Over Tungstencarbide Modified HZSM-5 Catalysts

The conversion of light alkanes into aromatic compounds mainly benzene, toluene and xylenes (BTX) is of great importance since BTX are basic organic chemical raw materials of chemical industry. Tungsten carbide (WC) has an analogouscatalytic activity with platinum and was widely applied in some catalytic reactions.Our previous work has proved that the introduction of WC has improved the catalytic activityof HZSM-5.However,since the dehydrogenation capacity of WC is limited, the catalytic activity of WC/HZSM-5 is far from the industrial demand., Ga/HZSM-5 and Zn/HZSM-5 were considered as the good aromatization catalystsas because Ga and Zn have an outstanding performance in dehydrogenation.In our study, Ga-WC/HZSM-5 and Zn-WC/HZSM-5bi-functional catalysts were prepared by reduction-carbonization and impregnation methods. Attribute to the synergistic effect between metal and WC, both the activity and stability of the catalysts have been enhanced.The samples were characterized byXRD、SEM、EDS、BET、FT-IR and TG methods.Then the aromatization of n-hexane was studied over the Ga-WC/HZSM-5 and Zn-WC/HZSM-5 catalysts. The role of metal components and the reaction mechanism were studied. The results showed that compared to WC/HZSM-5, Ga-WC/HZSM-5 and Zn-WC/HZSM-5, especially Zn-WC/HZSM-5, had a higher aromatic selectivity and aromatic yield. The pyridine FTIR result showed that introduction of Ga and Zn into WC/HZSM-5 lead to the redistribution in the type of acid sites on the surface of catalyst.It was found experimentally that a proper amount addition of Zn and Ga resulted in not onlythe higher selectivity of aromatization of n-hexane but also a decrease of coke deposition. The results show that the 1.5% Zn-WC/HZSM-5and 2% Ga-WC/HZSM-5 were the most active catalysts since the proportion of Lewisacid to Bronsted acid species isappropriate at that time.