Rh/SiO₂ Catalysts for Selective Reduction of NO with H₂ in the Presence of SO₂ and O₂

Abstract

Rh/SiO₂, as well as Ir/SiO₂, catalysts showed excellent activity for NO reduction with H₂ in the presence of O₂ and SO₂. In particular, the coexistence of O₂ and SO₂ was essential for NO reduction to occur. FT-IR measurements of the adsorbed species on Rh/SiO₂ catalyst indicated that NO adsorption was completely inhibited by SO₂ in the absence of O₂, but the adsorption of NO occurred on the vacant sites formed by the oxidation of SO₂ to SO₃ in the presence of O₂. NO reduction with H₂ probably proceeds via NH_x intermediate species as for NH₃- SCR. SiO₂ was the most effective support for rhodium. Other supports such as Al₂O₃ were not effective, possibly because activation of H₂ is hindered on more cationic rhodium (Rh^δ+) due to the presence of adsorbed SO₃ or NO₃ species on the supports.