Adsorption complexes that are formed by exposing Cu/ZSM-5 to nitric oxides have been identified by FTIR. Some of them are thermally decomposed below 200 degrees C, but others, though much more stable thermally, are reduced at low temperature by chemical interaction with gaseous propane. The FTIR spectra suggest that the latter complexes are nitro and/or nitrate groups associated with Cu ions. Their formation and reduction when Cu/ZSM-5 is exposed to NO + O-2 + C3H8 seems consistent with the assumption that they are intermediates in catalytic NOx reduction. Mass spectrometric analysis of the gases that are released when these complexes react with propane reveals formation of N-2, whereas thermal decomposition at higher temperatures only yields NO2, NO, H2O, traces of O-2, but no N-2. The results suggest that adsorbed NOy groups (y greater than or equal to 2) are able to abstract H atoms from hydrocarbon molecules.