EFFECT OF H2O AND SO2 ON THE ACTIVITY OF PD TIO2 CATALYSTS IN CATALYTIC REDUCTION OF NO WITH METHANE IN THE PRESENCE OF OXYGEN/

Effect of H2O and SO2 on the NO reduction activity of the Pd/titania c atalysts was examined in the NO+CH4+O-2 reaction. Steady-state and tra nsient response experiments were performed using a tubular flow reacto r. Isotopically labeled methane, (CH4)-C-13, was used in studying the transient behavior of the catalytic system. Reactor effluents were ana lyzed by using gas chromatography, mass spectrometry, and chemilumines cense techniques. Steady-state reaction experiments showed that the ca talyst has a high activity for reduction of NO over a wide oxygen conc entration range (0-9800 ppm at 500 degrees C). Higher N-2 selectivitie s (less NH3) and higher methane conversion values were obtained at hig her O-2 concentrations. Experiments also showed that NO conversion was not affected by the presence of water (up to 6%), and higher nitrogen selectivities were obtained at higher H2O concentrations in the feed. On the other hand, significant and irreversible loss of activity was observed in the presence of SO2. The reaction experiments indicated th e formation of SO3 and H2S over the catalyst. The post-reaction XPS an alysis of the catalyst samples showed that sulfate species were formed on the surface and that the surface palladium was completely converte d to pd(2+) State after being exposed to SO2. (C) 1998 Elsevier Scienc e B.V. All rights reserved.