The formation of nitrous oxide in the selective catalytic reduction of NO x 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/γ-Al 2 O 3 and CuO/TiO 2 monolithic catalysts. Textural properties and CuO crystal phases were analysed. Temperature-programmed desorption of NH 3 , NO, and NO 2 and X-ray photoelectron spectroscopy (XPS) after in situ adsorption of NO and NO 2 experiments were carried out. Even at low temperature, N 2 O generation takes place at a greater rate for the catalysts supported on titania than for those on alumina. In the case of alumina, the N 2 O concentration detected was independent of the CuO content. For the CuO/TiO 2 system it was associated with the active phase configuration. After in situ adsorption of NO and NO 2 , a band associated with nitrate species was identified in the XPS spectra. Adsorbed NO3− species seem to be responsible for the NO 2 , NO, and O 2 desorbed products detected in the NO x -TPD. The results suggests that NO3(ads)− along with NH x(ads) species, were involved in N 2 O formation at low temperature.