Using synchrotron radiation x-ray photoelectron spectroscopy we have determined the surface composition during the reduction reactions of nitric oxide with hydrogen and carbon monoxide on Pt(100). It is found that NO dissociates readily on this surface and that the dissociation product oxygen is only partially removed by reducing agents H-2 and CO. Two oxygen species have been identified after NO dissociation, and they appear to react with H-2 and CO at different rates. With increasing total pressures in the NO-H-2 reaction, new N-containing surface species are observed. Some preliminary results are presented concerning the reduction of NO in the presence of both CO and H-2. For this system partially hydrogenated CO molecules are found in addition to partially hydrogenated N-species. (C) 2003 American Institute of Physics.