The adsorption of organic nitro compounds such as nitromethane and nitroethane on different supported silver catalysts (Ag/Al2O3, Ag/TiO2, Ag/SiO2) has been studied using infrared spectroscopy. The adsorbed NCO species formation was strongly influenced by the catalyst support and therefore clearly detected on Ag/Al2O3 and Ag/TiO2 catalysts by thermal decomposition of nitromethane and nitroethane at temperatures higher than 150 degrees C. With the Ag/SiO2 catalyst, very little NCO formation was observed at 350 degrees C. On the other hand, the catalyst support was found to affect the N-2 formation in the selective reduction of NOx on supported silver catalysts. On the basis of these findings, the role of adsorbed nitromethane, nitroethane and isocyanate species in the selective reduction of NOx is discussed with respect to the catalyst support effect and the catalytic activity.