DECOMPOSITION OF AMMONIA ON O-COVERED AND S-COVERED RU(001) SURFACES

The decomposition of ammonia on oxygen- and sulfur-modified Ru(001) su rfaces was investigated at a surface temperature of 480 K using the th ermal desorption technique. On an O-covered Ru(001) surface, two therm al desorption peaks of nitrogen were observed. In addition to the broa d feature centered around 750 K, a sharp peak was observed at 640 K, g rowing in intensity with oxygen coverage. These results can be qualita tively explained by the repulsive interactions between the adsorbed ni trogen and oxygen atoms. Our work further revealed that sulfur adatoms significantly inhibit the decomposition of ammonia. At a sulfur cover age of 0.6, no nitrogen desorption could be detected. In contrast, the presence of oxygen adatoms on Ru(001) only slightly affected the amou nt of ammonia decomposed. The coverage of N(ads) from ammonia decompos ition on an O-saturated surface was similar to that on clean Ru(001).