| abstract |
Disclosed is a catalyst for catalytically reducing nitrogen oxides in an exhaust gas by contacting the exhaust gas which is generated by supplying and combusting a fuel under periodic rich/lean conditions. The catalyst is composed of (A) a catalyst component A which is composed of (a) ceria, (b) a praseodymium oxide, or (c) a mixture of oxides and/or a composite oxide of at least two elements selected from cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; (B) a catalyst component B which is composed of (d) a noble metal catalyst component comprising at least one substance selected from platinum, rhodium, palladium and their oxides and (e) a carrier; and (C) a catalyst component C which is composed of at least one of (f) a solid acid and (g) a solid acid supporting at least one oxide of at least one metal selected from vanadium, tungsten, molybdenum, copper, iron, cobalt, nickel and manganese. |