J. Mitome et al., EFFECT OF H2O AND SO2 ON THE ACTIVITY OF PD TIO2 CATALYSTS IN CATALYTIC REDUCTION OF NO WITH METHANE IN THE PRESENCE OF OXYGEN/, Catalysis today, 42(1-2), 1998, pp. 3-11
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.