Left: Oxidized vanadium V5+ supported on a single titanium oxide crystal (top) catalyzes the dehydration reaction of cyclohexane (C6H12) to become reduced vanadium V4+ (bottom). The addition of oxygen returns vanadium to its oxidized form. Right: An atomic-scale model of reduced vanadium4+ based on data from XSW experiments. Chemists who develop catalysts are always trying to improve catalytic efficiency or create novel reaction pathways, but they’re doing so largely in the dark. The atomic-scale structure and chemical properties of catalysts remain surprisingly mysterious, despite the critical roles that catalysts play in a variety of industrial and environmental applications. Heterogeneous catalysts—which differ in phase from their substrates—are used, for example, to convert toxic nitric oxide from automotive emissions to less harmful gases. Hoping to shed some light on how catalysts behave, and connect these behaviors to catalysts’ activity and selectivity, researchers working at the U.S. Department of Energy Office of Science’s Advanced Photon Source teased out structural and chemical information about a single layer of vanadium oxide, a catalyst, supported on the surface of a titanium oxide crystal. The data revealed that vanadium oxide undergoes a dramatic and reversible change in both chemical states and structure during a redox reaction cycle, providing unprecedented
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