(706g) Activation of CH4 over Aluminosilicate Zeolite

CH₄ and N₂O are the second and third major greenhouse gases after CO₂. Conversion of CH₄ and N₂O to value-added chemicals can not only increase the effective utilization of carbon and nitrogen but also reduce the emission of greenhouse gas, which is a subject of great economic and environmental significance. In the past decades, direct oxidation of methane to methanol or other value-added chemicals was highly depended on the transition or noble metal-loading catalysts [1, 2]. The preparation process of these catalysis is cumbersome, expensive, and not environmentally friendly.

In this study, transition-metal-free aluminosilicate zeolite catalysts were used in direct oxidation of methane for the first time and the unexpected activity was achieved in the presence of N₂O [3]. After screening more than 10 kinds of aluminosilicate zeolites with different structures and chemical compositions, Ferrierite (FER) zeolite revealed quite exceptional advantages in formation rate and stability of methanol production from methane. The distorted tetra-coordinated Al in the framework (Al_IV-2) and penta-coordinated Al on the extra framework (Al_V) formed during the activation and calcination processes were confirmed as the active centers. The stable and efficient methanol production capacity of FER zeolite was ascribed to the two-dimensional straight channels and its distinctive Al distribution of FER zeolite. Under the optimal reaction conditions, an unprecedented methanol formation rate of 136 μmol·g^-1·min^-1 with 88 % methanol selectivity and 11 % dimethyl ether (DME) selectivity was achieved, which was far beyond the best record in the literature and our recent achievements using transition-metal-containing catalysts.

This is the first report about transition-metal-free zeolite catalyzing methane to methanol with ultra-high methanol formation rate and selectivity.

References

1. Xiao, T. Yokoi, et.al., ACS Catal. 2023, 13,11057–11068
2. Xiao, T. Yokoi, et.al., Nature Commun. in press
3. Xiao, T. Yokoi, et.al., J. Am. Chem. Soc., in press