A NO.sub.x adsorber catalyst and its use in an emission treatment system for internal combustion engines, is disclosed. The NO.sub.x adsorber catalyst comprises a first layer consisting essentially of a support material, one or more platinum group metals disposed on the support material, and a NO.sub.x storage material.

A NO.sub.x adsorber catalyst and its use in an emission treatment system for internal combustion engines, is disclosed. The NO.sub.x adsorber catalyst comprises a first layer consisting essentially of a support material, one or more platinum group metals disposed on the support material, and a NO.sub.x storage material.

A catalytic converter with excellent OSC performance and NO.sub.x purification performance. The converter includes a substrate with a cell structure through which exhaust gas flows, and a catalyst layer formed on a cell wall surface of the substrate. The catalyst layer includes a lower catalyst layer and an upper catalyst layer, the lower catalyst layer being formed on a surface of the substrate, and the upper catalyst layer being formed on a surface of the lower catalyst layer. The upper catalyst layer includes at least a zirconia support with rhodium carried thereon, and two types of ceria-zirconia-based composite oxides with different specific surface areas, each of the ceria-zirconia-based composite oxides having no rhodium carried thereon. The lower catalyst layer includes an alumina support with platinum carried thereon, and a ceria-zirconia-based composite oxide.

A catalytic converter with excellent OSC performance and NO.sub.x purification performance. The converter includes a substrate with a cell structure through which exhaust gas flows, and a catalyst layer formed on a cell wall surface of the substrate. The catalyst layer includes a lower catalyst layer and an upper catalyst layer, the lower catalyst layer being formed on a surface of the substrate, and the upper catalyst layer being formed on a surface of the lower catalyst layer. The upper catalyst layer includes at least a zirconia support with rhodium carried thereon, and two types of ceria-zirconia-based composite oxides with different specific surface areas, each of the ceria-zirconia-based composite oxides having no rhodium carried thereon. The lower catalyst layer includes an alumina support with platinum carried thereon, and a ceria-zirconia-based composite oxide.

The object of the present invention is to provide an exhaust gas purifying catalyst that can achieve high purification performance while suppressing H.sub.2S emissions. The object is solved by an exhaust gas purifying catalyst in which the top layer of a catalyst coating layer comprises a ceria-zirconia composite oxide having a pyrochlore-type ordered array structure, in which the ceria-zirconia composite oxide contains at least one additional element selected from the group consisting of praseodymium, lanthanum, and yttrium at 0.5 to 5.0 mol % in relation to the total cation amount, and the molar ratio of (cerium+additional element):(zirconium) is within the range from 43:57 to 48:52.

The object of the present invention is to provide an exhaust gas purifying catalyst that can achieve high purification performance while suppressing H.sub.2S emissions. The object is solved by an exhaust gas purifying catalyst in which the top layer of a catalyst coating layer comprises a ceria-zirconia composite oxide having a pyrochlore-type ordered array structure, in which the ceria-zirconia composite oxide contains at least one additional element selected from the group consisting of praseodymium, lanthanum, and yttrium at 0.5 to 5.0 mol % in relation to the total cation amount, and the molar ratio of (cerium+additional element):(zirconium) is within the range from 43:57 to 48:52.

The exhaust gas purification device includes a substrate, a first catalyst layer, and a second catalyst layer. The substrate includes an upstream end, a downstream end, and a porous partition wall defining a plurality of cells extending between the upstream end and the downstream end. The plurality of cells include an inlet cell opening at the upstream end and sealed at the downstream end, and an outlet cell adjacent to the inlet cell sealed at the upstream end and opening at the downstream end. The first catalyst layer is disposed on a surface of the partition wall in an upstream region. In a downstream region, the second catalyst layer is disposed inside the partition wall, and a second catalyst-containing wall including the partition wall and the second catalyst layer has a porosity of 35% or more.

The exhaust gas purifying catalyst presented here includes a substrate and a catalyst coat layer formed on the surface of the substrate. The catalyst coat layer is formed in a laminate structure having two layers, with a first layer being nearer to the surface of the substrate and a second layer being relatively further from this surface. The second layer includes a carrier and a noble metal supported on the carrier. The first layer is a noble metal-free layer that does not contain a noble metal but does contain an OSC material having oxygen storage capacity.

The exhaust gas purifying catalyst presented here includes a substrate and a catalyst coat layer formed on the surface of the substrate. The catalyst coat layer is formed in a laminate structure having two layers, with a first layer being nearer to the surface of the substrate and a second layer being relatively further from this surface. The second layer includes a carrier and a noble metal supported on the carrier. The first layer is a noble metal-free layer that does not contain a noble metal but does contain an OSC material having oxygen storage capacity.

According to various aspects and exemplary embodiments of the present disclosure, ultra-small catalyst particles having extremely high reactivity may be synthesized in single-atom or single-molecule state. When the ultra-small-sized single-atom or single-molecule catalyst is used, the use of metal raw materials can be minimized and, at the same time, catalytic activity may be maximized through maximized reactivity of the single-atom or single-molecule catalyst.