Ammonia oxidation on Pt(410)

1The adsorption of both O-2 and NH3 on Pt(410) was studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Molecular NH3 desorbed from Pt(410) between 100 and 450 K, and dissociation was not observed. Radiation (X-rays, electrons) induced NH3ad dissociation, and as a result several dissociation products (NH2ad, NHad, and N-ad) were observed in the N 1s core-level spectrum. NHd is a rather stable dissociation product that starts to dehydrogenate above 350 K. The Nad and Had formed in this process desorbed on formation (as N-2 and H-2). Both molecular and dissociative O-2 adsorption were observed after the surface was exposed to O-2(g) at 100 K. Molecularly adsorbed O-2 desorbed below 200 K, whereas atomic oxygen desorbed (as O-2) between 600 and 900 K, in two distinct desorption peaks. In the O 1s core-level spectrum, both molecular O-2 and two different types of O-ad were distinguished. NHad dissociation was observed on an oxygen-presaturated surface. The NH3ad oxy-dehydrogenation started at 150 K. NOad and NO(g) were also observed, but only during experiments in which an excess of Oad was available. NOad desorbed/decomposed between 400 and 500 K. For the steady-state ammonia oxidation reaction, N-2 and H2O were the major products at low temperatures, whereas the selectivity toward NO and H2O changed at higher temperatures. This selectivity change can be attributed to changes in surface composition. (c) 2006 Elsevier Inc. All rights reserved.