Computational Insight into Methane–Methanol Coupling and Aromatization over Metal-Modified ZSM-5: From Mechanism to Catalyst Screening

ZSM-5 zeolite modified by molybdenum is one of the promising catalysts for methane dehydroaromatization (MDA). The introduction of methanol to couple with methane over metal-modified ZSM-5 can facilitate the MDA reaction, but the reaction mechanism, optimal energy pathways, and kinetic and selectivity controlling factors remain to be clarified. In this study, periodic density functional theory (DFT) calculations were performed to investigate the mechanism of methane-methanol coupling and aromatization over Mo/ZSM-5. The calculation results showed that the process of methane-methanol coupling to light olefins (mainly ethylene and propylene) was determined by the C-C coupling step, while further aromatization of the ethylene and propylene intermediate was kinetically controlled by the dehydrogenation step involved in the regeneration of the Brønsted acid site over Mo/ZSM-5. The co-adsorption of H2O produced from methanol dehydration had little effect on methane-methanol coupling to ethylene but increased the rate-limiting barrier for ethylene aromatization to benzene. To further improve the catalytic performance of Mo/ZSM-5, we found that introducing a second metal component such as Co, Ni, or Nb into Mo/ZSM-5 could promote the C-C coupling process and enable these bimetallic combinations to be promising candidates for methane-methanol coupling reactions.