Non-oxidative Aromatization Of Methane Over Molding Mo/ZSM-5 Catalyst

Non-oxidative aromatization of methane is an important reaction in methane direct conversion, and further industrial application is a significant research topic at present. Mo/ZSM-5 was chosen to study the effect of the molding binder, molding procedure and method in methane non-oxidative aromatization. The influence of the reaction conditions on the activity, selectivity and the stability of the molding Mo/ZSM-5 catalyst was also investigated. It is expected to provide useful information for industrial application.The effect of physicochemical property of ZSM-5 on methane aromatization was investigated firstly. The results showed that the ZSM-5 with relative low nSi/nAl ratio is beneficial for the reaction. Simultaneously the ZSM-5 with the particle size of 100 nm-1μm is favorable for Mo species dispersing and goal products diffusion, and the catalysts showed high activity and low coke selectivity. Therefore it is the suitable catalyst support.The influence of different molding binder was studied by extrusion process. It is found that the binder changed the diffusion of the ZSM-5 and the redox of Mo species greatly, and the activity of the catalyst was affected obviously; the catalyst extruded with ZnO showed higher aromatization performance than that of the Mo/ZSM-5; the activity of catalyst extruded with SiO2 was 80% of the base. However, the mechanical strength of the catalysts was only enhanced by the introduction of SiO2 and Al2O3. When the mixed Al2O3-ZnO compounds were used as the binder, the mechanical strength of the molding catalysts was about 70 N/cm, and the diffusibility of catalyst and reducibility of Mo species was kept well due to the formation of ZnAl2O4 under the reaction conditions. The activity of the extruded catalyst with Al2O3-ZnO showed 90% of that of the base catalyst. Therefore, SiO2 and Al2O3-ZnO are good binder for molding Mo/ZSM-5 catalyst in methane aromatization.The study of extrusion procedure showed that the catalyst prepared with Mo species impregnation onto the extruder of binder and ZSM-5 possesed better crushing strength as well as stabilized the production of benzene. Meanwhile, it was found that both diffusibility and Mo species dispersibility are the keves to enhance the catalystic performance of the molding catalyst. This result was confirmed further by the addition of pore-forming agent with smaller molecular weight and the alkaline impregnating solution. The laminar Mo/ZSM-5 catalyst with a spherical shell was prepared by granulation process; the laminar thickness of the catalyst was 1/10-1/4 of the extruded one. The results indicated that the shortening of diffusion path is an effective way to improve the diffusivity of molding catalysts. The selectivity of aromatics increased 25% and the content of coke decreased 12% than that of the extruded catalysts. When the nonporous inert ceramic ball with the particle size of 0.5 mm was used as the substrate, the best performance of laminar catalyst was obtained. At 960 mL/gZSM-5·h space velocity, the selectivity of aromatics, the content of C2 and the content of coke was 56.2%,12% and 29.3%, respectively. The catalyst also showed better stability in the 500 min reaction.