Brønsted Acid Site Catalytic Role in Methane Dehydroaromatization over Mo/HZSM-5

Methane dehydroaromatization (MDA) has the potential to be a technology with high environmental efficiency for synthesizing benzene, toluene, and xylenes (BTX) from nonpetroleum feedstocks in a carbon-neutral society. However, a debate presently exists concerning the reaction mechanism of MDA catalysis by the promising Mo/HZSM-5, primarily attributed to the unclear catalytic role of strong Brønsted acid sites (BAS), which significantly hampers the development of highly active and anticoking catalysts. This study aims to resolve the controversy surrounding strong BAS in MDA by comparing the silica zeolite with supported molybdenum (Mo/Bsn-S-1) with Mo/HZSM-5. The Mo/Bsn-S-1 featuring internally anchored molybdenum species was prepared to generate a strong metal–support interaction, which resolved the problem, leading to the incomparable catalytic activity of Mo/Silicalite-1 with Mo/HZSM-5, due to the absence of anchoring sites. By physically mixing the Mo/Bsn-S-1 with HZSM-5 and comparing it to bifunctional catalysts, the study reveals that MDA follows a bifunctional mechanism, predominantly through the hydrocarbon pool mechanism, where strong BAS play a facilitating role. This study demonstrates that strong BAS located in spatial proximity to molybdenum species improve the aromatics yield via the autocatalytic reactions of hydrocarbon pool, while those not in spatial proximities catalyze the cyclization and polycondensation of intermediates into polycyclic aromatics and coke. This study provides crucial evidence in clarifying the debate over the role of strong BAS in MDA and lays an important theoretical foundation for the design of catalysts that better utilize BAS to balance catalytic activity and resistance to coking.