Enhanced dehydroaromatization of methane with methanol on Mo-ZSM-5/ZSM-11 intergrown zeolite materials

Abstract

Methane dehydroaromatization (MDA) represents an appealing route for the direct utilization of abundant methane resources. Currently, the major challenge of MDA reaction lies in the rapid catalyst deactivation via coke formation, hindering large-scale industrialization of the process. Herein we report an enhanced conversion route of MDA in the presence of methanol on Mo-based zeolite materials. Compared to regular ZSM-5, ZSM-11, and their mechanically mixed counterparts, Mo embedded in ZSM-5/ZSM-11 intergrown matrix exhibits higher methane conversion (16.0%) and aromatics selectivity (62.5%) while limiting coke production to 12.1% under the co-feeding of methane and methanol (nCH4/nCH3OH = 30). If no methanol addition, coke selectivity is up to 45.1% in MDA reaction. Additionally, hydrogen enriched syngas (nH2/nCO = 6) was obtained as a co-product of the methane and methanol co-aromatization. NH3-adsorbed 1H MAS NMR, Co2+ titrated UV-vis and Raman spectroscopy characterizations reveal that a proper amount of Brönsted acid sites and the binuclear Mo anchored on the Al pairs at the intersection cavity may account for the superior reaction performance of the intergrown zeolites. A catalytic mechanism was also proposed via 13CH3OH isotopic labeling tracer and in-situ13C solid-state NMR studies. Methanol is first decomposed into CO/H2, while CO is hydrogenated to CH4 and converted into CO2 via the water-gas shift reaction. Alternatively, methanol is converted into CO/CO2 through formate intermediates. Subsequently, CO2 reduces coke deposition via the reverse Boudart reaction, which improves the catalytic performance.