Designing Reactive Bridging O2- at the Atomic Cu-O-Fe Site for Selective NH3 Oxidation.

ABSTRACT

Surface oxidation chemistry involves the formation and breaking of metal-oxygen (M-O) bonds. Ideally, the M-O bonding strength determines the rate of oxygen absorption and dissociation. Here, we design reactive bridging O2- species within the atomic Cu-O-Fe site to accelerate such oxidation chemistry. Using in situ X-ray absorption spectroscopy at the O K-edge and density functional theory calculations, it is found that such bridging O2- has a lower antibonding orbital energy and thus weaker Cu-O/Fe-O strength. In selective NH3 oxidation, the weak Cu-O/Fe-O bond enables fast Cu redox for NH3 conversion and direct NO adsorption via Cu-O-NO to promote N-N coupling toward N2. As a result, 99% N2 selectivity at 100% conversion is achieved at 573 K, exceeding most of the reported results. This result suggests the importance to design, determine, and utilize the unique features of bridging O2- in catalysis.