CATALYST AND CATALYST STRUCTURE FOR REDUCTION OF NITROGEN OXIDES, AND METHOD FOR CATALYTIC REDUCTION OF NITROGEN OXIDES

摘要

A catalyst which comprises: a surface catalyst layer having a catalystingredient (A) comprising at least one member selected among solid acids andsolid acids having, deposited thereon, an oxide and/or ions of at least oneelement selected among vanadium, tungsten, molybdenum, copper, iron, cobalt,nickel, and manganese; and an inner catalyst layer comprising a combination ofa noble-metal catalyst ingredient (B) comprising at least one member selectedamong platinum, rhodium, palladium, and oxides of these and a catalystingredient (C) comprising ceria, praseodymium oxide, or an oxide mixtureand/or composite oxide of at least two elements selected among cerium,zirconium, praseodymium, neodymium, terbium, samarium, gadolinium, andlanthanum. The catalyst is for use in catalytically reducing nitrogen oxidescontained in an exhaust gas after a fuel is fed and burned under periodicrich/lean conditions; the resultant exhaust gas is brought into contact withthe catalyst to catalytically reduce the nitrogen oxides. The method comprisesbringing nitrogen oxides into contact with the catalyst to catalyticallyreduce the nitrogen oxides.