Catalyst Active Site Revealed

By coupling materials synthesis and catalytic-activity studies with a powerful NMR spectroscopy method, a team of researchers at Pacific Northwest National Laboratory, in Richland, Wash., and the Dalian Institute of Chemical Physics in China has identified the active species in a molybdenum-based zeolite (aluminosilicate) catalyst that converts methane to benzene. It is an aluminum-oxygen-molybdenum linkage (J. Am. Chem. Soc., DOI: 10.1021/ja7110916). The study could lead to efficient methods for transforming methane into more valuable and easily transported liquids, which in turn could provide the chemical industry with incentives to tap supplies of natural gas in remote areas.

To boost ordinarily weak Mo NMR signals, Heng Zheng, Xinhe Bao, and coworkers prepared a series of catalysts from a ⁹⁵Mo-enriched precursor material, evaluated the materials' catalytic activities, and used an ultra high-field NMR method to probe the samples. On the basis of those measurements, the team concluded that during catalyst preparation molybdenum atoms migrate into the zeolite channels and anchor onto acidic aluminum sites, thereby forming Al???O???Mo linkages. These structures serve as catalytically active centers in the methane-conversion reactions.