Molybdenum/ZSM-5 Catalyzes Methane Co-Aromatization with Furan

The direct conversion of methane into higher-value chemicals remains challenging due to methane's inert C–H bonds and the tendency for coke formation on catalysts. Methane dehydroaromatization MDA over transition-metal–modified ZSM-5 catalysts, notably Mo/ZSM-5, is a leading route under investigation. Co-feeding strategies with small-molecule co-reactants have shown to mitigate catalyst deactivation and extend reactor lifetimes. Biomass-derived furanic compounds such as furan, furfural, 2-methylfuran, and 5-hydroxymethylfurfural are platform molecules obtainable from lignocellulose and used for aromatics production via pathways including Diels–Alder condensation, decarbonylation, oligomerization, and alkylation on acidic zeolites. In particular, co-aromatization of methane with furan is proposed to facilitate methane activation and raise aromatics selectivity, with limited oxygen in furan aiding oxidative cleaning of carbonaceous deposits and potentially improving long-term stability.

Experimental approach

The study employed solid-state nuclear magnetic resonance spectroscopy in combination with online mass spectrometry using the HPR-20 gas-analysis system to examine the reaction mechanism over Mo/ZSM-5. The focus was to assess the impact of furan co-feeding on methane aromatization and Mo speciation. Online MS analysis of the first 30 minutes showed faster consumption of oxygen-containing products (H2O, CO, CO2) under furan co-feeding than in methane-only MDA, and a notably shorter activation period for ethylene and benzene production (about 5 minutes vs about 8 minutes).

Spectroscopic observations on Mo speciation

1H–95Mo solid-state NMR correlation spectroscopy tracked Mo species evolution. The fresh Mo/ZSM-5 exhibited peaks corresponding to exchanged Mo-oxo precursors. After 5 minutes of methane-only reaction, these species were partially reduced to form MoOxCy-I. In contrast, 5 minutes of methane co-fed with furan yielded a more complex active state, with MoOxCy-I and a distinct MoOxCy-II species formed, indicating accelerated formation of active Mo centers under co-feeding.

The integrated MS results with the NMR data support MoOxCy-II as an active species for MDA over Mo/ZSM-5, highlighting the critical role of furan co-feeding in accelerating the development of the active Mo configuration.

Implications

The findings indicate that furan co-feeding not only speeds up active-site formation but may also contribute to longer-term catalyst stability by enabling selective oxidation of carbonaceous deposits via oxygen in furan. This mechanistic insight complements existing co-feed strategies to boost methane activation toward aromatics on Mo/ZSM-5 catalysts.

Paper reference: Gao W, Qi G, Wang C, Wang Q, Liang J, Xu J, Deng F. Molybdenum/ZSM-5 Catalyzes Methane Co-Aromatization with Furan: Unveiling the Mechanism with Solid-State NMR. ACS Catal. 2024, 14, 11, 8220–8231.

Project summary: Dr. Guodong Qi, Prof. Xu Jun and Prof. Feng Deng, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, China.