Adsorption of CO on Cu/ZrO2 leads to the formation of Cu+-CO (2126 cm(-1)) and Zr4+-CO (2192 cm(-1)) carbonyls and of carbonato-hydrogen-carbonate structures (bands in the 1650-1000 cm(-1) region). Adsorption of NO on the same sample produces bands characterizing N2O (2246 cm(-1)), NO+ (2122 cm(-1)), mononitrosyls coordinated to Cu+ (1759 cm(-1)) and Cu2+ (1872 cm(-1)) ions, respectively, and nitro (1527, 1327 cm(-1)) and nitrito compounds (1185 cm(-1)). Introduction of oxygen into the system results in an initial increase in concentration of NO2- compounds followed by oxidation of these complexes to nitrates (1630, 1580, 1554, 1287, 1225, 1031, and 1004 cm-1). The nitrates thus obtained are stable up to 573 K. They enhance the Lewis acidity of the neighboring Zr4+ sites on the support as a result of which mononitrosyls of the Zr4+(NO3)-NO type (1932 cm(-1)) are formed. The copper nitrates formed on the surface begin to react with C2H4 at 523 K, yielding an organic nitro-containing deposit which decomposes to reactive cyanides (2142 cm(-1)). The mechanism of selective catalytic reduction of nitrogen oxides with hydrocarbons on Cu/ZrO2 and the oxidation state of the copper ions during the process are discussed.