Preparation of highly active binder-added MoO3/HZSM-5 catalyst for the non-oxidative dehydroaromatization of methane

The present article compares the CH4 dehydroaromatization activities of binder-added MoO3/HZSM-5 catalysts prepared via three different procedures with the activity of a 3 Wt.% MoO3/HZSM-5 base catalyst prepared using the conventional impregnation method at 973 K. The aim of the comparison is to search a way to prepare a practically useful and highly active binder-added MoO3/HZSM-5 catalyst for the title reaction. The procedures attempted were (a) impregnation of MoO3 over a wet mixture of HZSM-5 and a binder SiO2 or Al2O3 followed by calcination, (b) impregnation of MoO3 on HZSM-5 followed by a wet mixture of the resulting sample with one binder and then calcination, and (c) carburization of MoO3 pre-impregnated on HZSM-5 followed by a wet mixture of the carburized MoO(3/)HZSM-5 with one binder, respectively. For the catalysts prepared via Procedure (a), nearly a linearly decreased benzene formation activity was observed with increasing SiO2 to HZSM-5 weight ratio, confirming a wasteful load of MoO3 on the added binder for the nonselective adsorption of MoO3 in impregnation. Impregnation of MoO3 On HZSM-5 prior to the wet Mixture (Procedure (b)) was then attempted to increase the concentration of MoO3 On the HZSM-5 component in the final catalysts and thus their activities, but the activities reached were hardly over one-third of the activity of the base catalyst, indicating that the procedure is unable to attain the purpose. The Cause, confirmed by comparative MoO3 adsorption tests, was the migration of MoO3 from its primary Support HZSM-5 onto the binder in the wet mixture step in hot water to lower the content of MoO3 on the HZSM-5. At last carburization of MoO3/HZSM-5 prior to its mixture with any of the binders was performed to localize MoO3 on the HZSM-5 and improve the activity of the final catalysts. As expected, the catalysts showed much higher benzene formation activities, reaching 85-90% of the activity provided by the base catalyst. Alteration of the primary support from HZSM-5 to the binders, however, brought the catalysts much lower activities. These together indicate that Procedure (c) certainly allows a Successful localization of MoO3 on its primary support HZSM-5 and therefore presents an applicable way of preparing highly active binder-added Mo/HZSM-5 catalysts for the non-oxidative dehydroaromatization of methane. (C) 2008 Elsevier B.V. All rights reserved.