Positive effect of coexisting SO2 on the activity of supported iridium catalysts for NO reduction in the presence of oxygen

Silica-supported iridium catalyst showed excellent activity for NO reduction with H-2 in the presence Of O-2 and SO2. This reaction took place only on Ir and Rh/SiO2, whereas on Pt, I'd and Ru/SiO2 SO2 showed inhibiting effect on NO reduction. SiO2 was the only effective support for In The most outstanding feature was that the coexistence Of O-2 and SO2 is essential for NO reduction to occur. The NO reduction activity did not change much in the presence of 10-150 ppm Of SO2, and H2O did not affect the activity, either. Concerning O-2 Concentration, only a small amount Of O-2 was sufficient for the activity increase and further increase Of O-2 concentration decreased NO conversion. The increase of IT loading and H-2 amount enhanced NO conversion. Accordingly, NO conversion of more than 40% was obtained in the presence of 10% O-2 at a space velocity of 50,000 h(-1). The FT-IR study revealed that the presence Of O-2 and SO2 promoted the adsorption of NO and formation of NH, species on Ir/SiO2. (C) 2002 Elsevier Science B.V. All rights reserved.