Insights into the coking and regeneration processes of methanol promoted methane dehydroaromatization reaction over Mo-ZSM-5/ZSM-11 intergrown zeolites

Abstract

The coke deposition in methane dehydroaromatization (MDA) can be significantly reduced in the presence of methanol. Nevertheless, the coking and regeneration processes still need to be further understood for industrial application of the MDA reaction. Herein, the effects of methanol on the Mo species and coke formation during the reaction-regeneration cycles of Mo-ZSM-5/ZSM-11 intergrown zeolites in the methane and methanol co-aromatization were studied by means of XRD, TG/DTG, TPO, XPS, Raman, and solid-state NMR etc. Addition of methanol reduced the integral coke formation rates and preserved more noncarbidic molybdenum species, thereby suppressing generation of aromatic-type coke and the coke on the zeolite surface. Mo-ZSM-5/ZSM-11 intergrown zeolites were reversibly regenerated under oxidative conditions at 470 °C, however, the catalyst underwent irreversible deactivation above 555 °C. During successive reaction-regeneration cycles, the dealumination of zeolites and part of active Mo species transform into inactive and non-regenerative Al₂(MoO₄)₃ are the main reasons for deactivation.