The formation of nitrous oxide in the selective catalytic reduction of NO,, with ammonia was studied in nitric acid plant exhaust gas under low-temperature conditions. The important role played by the Support in this process was evidenced by a comparison of CuO/gamma-Al2O3 and CuO/TiO2 monolithic catalysts. Textural properties and CuO crystal phases were analysed. Temperature-programmed desorption of NH3, NO, and NO2 and X-ray photoelectron spectroscopy (XPS) after in Situ adsorption of NO and NO2 experiments were carried out. Even at low temperature, N2O generation takes place at a greater rate for the catalysts supported on titania than for those on alumina. In the case of alumina, the N2O concentration detected was independent of the CuO content. For the CuO/TiO2 system it was associated with the active phase configuration. After in situ adsorption of NO and NO2, a band associated with nitrate species was identified in the XPS spectra. Adsorbed NO3- species seem to be responsible for the NO2, NO, and O-2 desorbed products detected in the NOx-TPD. The results suggests that NO3(ads)- along with NHx(ads) species, were involved in N2O formation at low temperature. (C) 2004 Elsevier Inc. All rights reserved.