A three-way catalyst article is provided for the treatment of exhaust gas from a positive ignition engine, the catalyst article comprising: a substrate having a first layer provided thereon, wherein a second layer is provided on the first layer, wherein the first layer comprises a first metal and a first alumina, and wherein the second layer comprises a second metal and a second alumina, wherein either (i) the first metal is Pd and the second metal is Rh; or (ii) the first metal is Rh and the second metal is Pd; and wherein at least one of the first and second aluminas comprises theta alumina.

The invention relates to aprocess for producing a catalyst comprising an intermetallic com-pound comprisingmixing of a salt comprising a metal selected from the group consisting of Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Auand Ru, a salt comprising a metal selected from the group consist-ing of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba,Sc, Y, La and the lanthanides, and a reducing agentcomprising a salt,wherein the mixing is carried out at a temperature where all compo-nents are solid; reacting the mixture obtained to form an intermetallic compound by heating said to a temperature in the range between the melting temperature of thereducing agent and the melting temperature of the intermetallic compound and holdingthe temperaturefor1 minute to 600 minutes; and washing the mixture to removeby-products andremainders of the salt of the cations of the reducing agent and at least one of the anions of the salts used in the first step. The invention further relates to a catalyst obtained by the process.

A NO.sub.x adsorber catalyst composition, 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 composition a support material and one or more platinum group metals disposed on the support material, wherein the support material comprises a NO.sub.x storage enhancer.

A NO.sub.x adsorber catalyst composition, 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 composition a support material and one or more platinum group metals disposed on the support material, wherein the support material comprises a NO.sub.x storage enhancer.

An exhaust gas purification catalyst comprises a substrate; a catalyst layer formed on the substrate and containing at least palladium (Pd) and rhodium (Rh) as a metal functioning as an oxidation and/or reduction catalyst. The catalyst also comprises a carrier that supports the metal, and an OSC material having oxygen storage capacity. The catalyst layer has, when disposed in the exhaust pipe, a front section positioned upstream in an exhaust gas flow direction within the exhaust pipe, and a rear section positioned downstream of the front section in the exhaust gas flow direction. The front section contains palladium (Pd) but does not contain the OSC material, and a proportion, at which the front section is formed from an upstream leading end in the exhaust gas flow direction, is 10% to 40% with respect to 100% of a total length of the substrate.

Described herein are heterogeneous materials comprising a mixture of a first n-type semiconductor and a second n-type semiconductor. The first n-type semiconductor may be a single or plural phase TiO.sub.2 material. The second n-type semiconductor includes a metal titanate and/or a noble metal. Upon activation with ultraviolet light, the photocatalytic material mixtures described herein efficiently decompose volatile chemical compounds. Furthermore, the photocatalytic materials disclosed herein are observably more stable, relative to known semiconductor materials, to inactivation by deposition.

Described herein are heterogeneous materials comprising a mixture of a first n-type semiconductor and a second n-type semiconductor. The first n-type semiconductor may be a single or plural phase TiO.sub.2 material. The second n-type semiconductor includes a metal titanate and/or a noble metal. Upon activation with ultraviolet light, the photocatalytic material mixtures described herein efficiently decompose volatile chemical compounds. Furthermore, the photocatalytic materials disclosed herein are observably more stable, relative to known semiconductor materials, to inactivation by deposition.

The invention provides an emission control system for treatment of an exhaust gas stream that includes an oxidation catalyst composition disposed on a substrate in fluid communication with the exhaust gas stream; at least one selective catalytic reduction (SCR) composition disposed on a substrate downstream from the oxidation catalyst composition, and a hydrogen injection article configured to introduce hydrogen into the exhaust gas stream upstream of the oxidation catalyst composition or downstream of the oxidation catalyst composition and upstream of the at least one SCR composition. The invention also provides a method of treating an exhaust gas stream, the method including receiving the exhaust gas stream into the emission control system of the invention and intermittently introducing hydrogen upstream of the oxidation catalyst article or downstream of the oxidation catalyst article and upstream stream of the SCR article.

The invention provides an emission control system for treatment of an exhaust gas stream that includes an oxidation catalyst composition disposed on a substrate in fluid communication with the exhaust gas stream; at least one selective catalytic reduction (SCR) composition disposed on a substrate downstream from the oxidation catalyst composition, and a hydrogen injection article configured to introduce hydrogen into the exhaust gas stream upstream of the oxidation catalyst composition or downstream of the oxidation catalyst composition and upstream of the at least one SCR composition. The invention also provides a method of treating an exhaust gas stream, the method including receiving the exhaust gas stream into the emission control system of the invention and intermittently introducing hydrogen upstream of the oxidation catalyst article or downstream of the oxidation catalyst article and upstream stream of the SCR article.

An exhaust gas cleaning catalyst is provided with a fire-resistant three-dimensional structural body, a first catalyst layer provide on a first surface side of the fire-resistant three-dimensional structural body, and a second catalyst layer provided on a side of the first catalyst layer opposite to the fire-resistant three-dimensional structural body. The first catalyst layer contains: a complex oxide including cerium and zirconium; and elemental rhodium. The second catalyst layer contains: a complex oxide including cerium and zirconium; and elemental palladium. The amount of cerium included in the second catalyst layer, in terms of cerium dioxide, is 10-25 g per liter of the fire-resistant three-dimensional structural body.