Positive effect of coexisting SO_2 on the activity of silica supported rhodium catalysts for NO reduction with hydrogen in the presence of oxygen

摘要

Rh/SiO_2 and Ir/SiO_2 showed excellent activity for NO reduction with H_2 in the presence of O_2 and SO_2, whereas Ru/SiO_2, Pd/SiO_2, and Pt/SiO_2 did not. The most outstanding feature of this reaction is that the coexistence of O_2 and SO_2 is essential for NO reduction to occur. FT-IR measurements of adsorbed species on Rh/SiO_2 indicated that, while NO adsorption was completely inhibited by SO_2 when O_2 was not present, the adsorption of NO was made possible on some vacant sites formed by oxidation of SO_2 to S03 in the presence of O_2. It was also suggested that NO reduction with H_2 proceeds via NHx intermediate species as well as for NH_3-SCR. SiO_2 was the most effective support for rhodium. One of the reasons why the other supports such as Al_2O_3 are not effective would be that the activation of H_2 is hindered on more cationic rhodium due to the presence of adsorbed SO_2 or NO_3 species on the supports.