Transient Oxygen States in Catalysis: Ammonia Oxidation at Ag(111)

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• 作者：Albert F. Carley ; Philip R. Davies ; M. Wyn Roberts ; Kevin K. Thomas
• 刊名：Langmuir
• 出版年：2010
• 出版时间：November 2, 2010
• 年：2010
• 卷：26
• 期：21
• 页码：16221-16225
• 全文大小：825K
• 年卷期：v.26,no.21(November 2, 2010)
• ISSN：1520-5827

文摘

Although the reactive sticking probability of oxygen at Ag(111) is of the order of 10⁻⁶ at 295 K, ammonia oxidation is a facile process at low temperatures. A combination of quantitative analysis of photoelectron spectra together with high resolution electron energy loss spectroscopy provides kinetic and spectroscopic evidence for an ammonia−dioxygen complex, stable at 100 K, as the key intermediate. The reactive oxygen O₂(s) is a transient dioxygen precursor of the unreactive peroxo state O₂^δ−(a). It is present as a complex when ammonia and dioxygen are coadsorbed at low temperature (100 K) with evidence from both O(1s) and energy loss spectra. Hydroxyl and amide/imide species are formed, followed by dehydroxylation and “oxide” formation at 260 K. This is a further example (zinc was the first) of how an sp-metal, where dioxygen bond cleavage is slow, provides an alternative pathway via a transient dioxygen state to catalytic oxidation through precursor assisted dioxygen bond cleavage. Whether it is a general characteristic of sp-metals remains to be established. Comparisons are made with the homogeneously catalyzed Gif reaction, the selective oxidation of hydrocarbons by dioxygen.