Tandem dual bed Mo/HZSM-5 and Mo/HMCM-22 catalysts with enhanced catalytic performance for natural gas conversion to aromatics

Abstract

Natural gas / methane conversion to aromatics and hydrogen through non-oxidative dehydroaromatization reaction is an attractive way for C1 utilization. In this contribution, the thermal stability of high (12 wt%) and low (5 wt%) Mo loading catalysts on HZSM-5 and HMCM-22 zeolites was studied under different pretreatment conditions. It was found that using reductive pretreatment, especially pretreated with CH4 + H2 mixtures, Mo catalysts exhibited high thermal stability with well-kept zeolite structure, resulting in enhanced catalytic performance for methane non-oxidative dehydroaromatization to aromatics. About 7% benzene yield obtained on 12 wt% Mo/HMCM-22 catalyst at 700 °C. On the contrary, the zeolite structure was collapsed as the catalysts pretreated with inert gas or air due to the formation of Al2(MoO4)3, as confirmed by XRD and 27Al solid NMR. When the catalysts were applied to natural gas conversion, the tandem dual bed 12 wt% Mo/HMCM-22 and 12 wt% Mo/HZSM-5 catalysts exhibited excellent catalytic performance using CH4 + H2 pretreatment. At 650 °C, 9% stable benzene yield was achieved over 120 h reaction time for a single run, taking advantages of high benzene yield from Mo/HMCM-22, and good stability from Mo/HZSM-5 catalysts, with great potential for commercial applications.