In situ DRIFTS characterization of wet-impregnated and sol-gel Pd/TiO2 for NO reduction with CH4

The adsorption/desorption behavior of 2%Pd/TiO2 catalysts synthesized by wet-impregnation and modified sol-gel techniques were examined in NO-CH4-O-2, reaction using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalyst prepared by the modified sol-gel method showed significantly higher resistance toward oxygen while maintaining a 100% NO conversion. Under NO + CH4 + O-2 flow, the main adsorbed NO species was identified as the linearly adsorbed NO on metallic palladium (Pd-0-NO) at high temperatures. On the oxidized sample, the major NO species was found to be a bridged nitrate species. Pd-0-NO species was suggested to react with CHx to form surface NHx species. Over the sol-gel catalyst, the peak intensity for Pd-0-NO species was much higher than that over the impregnated catalyst. The DRIFTS data seem to suggest that this species could play a role in reduction of NO with CH4 over Pd/TiO2 catalysts. (C) 2002 Published by Elsevier Science B.V.