Gas-Phase Reactions of Copper Oxide Cluster Cations with Ammonia: Selective Catalytic Oxidation to Nitrogen and Water Molecules.

Reactions of copper oxide cluster cations, Cu O ( n = 3-7; m ≤ 5), with ammonia, NH, are studied at near thermal energies using a guided ion beam tandem mass spectrometer. The single-collision reactions of specific clusters such as CuO, CuO, CuO, CuO, and CuO give rise to the release of HO after NH adsorption efficiently and result in the formation of Cu O NH. These Cu O clusters commonly have Cu average oxidation numbers of 1.0-1.4. On the other hand, the formation of Cu O H, i.e., the release of HNO, is dominantly observed for CuO with a higher Cu oxidation number. Density functional theory calculations are performed for the reaction CuO + NH → CuONH + HO as a typical example of HO release. The calculations show that this reaction occurs almost thermoneutrally, consistent with the experimental observation. Further, our experimental studies indicate that the multiple-collision reactions of CuO and CuO with NH lead to the production of Cu and CuO, respectively. This suggests that the desirable NH oxidation to N and HO proceeds on these clusters.