Our previous studies [Catal. Commun., in press; J. Catal., in press] on sol-gel-prepared I'd catalysts for reduction of NO with CH4 suggested that one of the key surface species for the NO-CH4-O-2 reaction involved NHx species. In this study, the use of NH3 as the reducing agent for NO reduction on the Gd-Pd/TiO2 catalyst was investigated under steady-state conditions. Also, temperature-programmed desorption using mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study the adsorption/desorption characteristics of NH3 on Gd-Pd/TiO2. It was found that NH3 was effective in reduction of NO on the reduced catalyst in the absence of O-2 at 300degreesC (100% NO conversion). This result was consistent with our earlier suggestion that NHx species formed through the interaction of methane and NO adspecies could act as a reducing agent for Pd-NO species. In the presence of O-2, however, NH3 oxidation takes place faster than NO reduction and NO conversion decreased. Our NH3-TPD experiments indicated that the reversible NH3 adsorption capacity was higher on the reduced catalyst compared to the oxidized catalyst. Also, there was a strong evidence obtained by DRIFTS that adsorbed NH3 is transformed into monodentate nitrate species on the oxidized catalyst. (C) 2002 Elsevier Science B.V. All rights reserved.