Positive effect of coexisting SO_2 on the activity of supported iridium catalysts for NO reduction in the presence of oxygen

摘要

Silica-supported iridium catalyst showed excellent activity for NO reduction with H_2 in the presnece of O_2 and SO_2. This reaction took place only Ir and Rh/SiO_2, whereas on Pt, Pd and Ru/SiO_2 SO_2 showed inhibiting effect on NO reduction. SiO_2 was the only effective support for Ir. The most outstanding features was that the coexistence of O_2 and SO_2 is essential for NO reduction to occur. The NO reduction activity did not change much in the presence of 10-150 ppm of SO_2, and H_2O 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 Ir 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 SO_2 promoted the adsorption of NO and formation of NH_x species on Ir/SiO_2.