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).