Provided is an exhaust gas purification catalyst that suppresses phosphorus poisoning and improves long-term durability. The exhaust gas purification catalyst includes a phosphorus collection layer and a catalyst layer containing at least one precious metal element MP selected from the group consisting of Pt, Pd, and Rh, wherein the phosphorus collection layer is arranged on the upper layer side and/or the upstream side with respect to the catalyst layer; the phosphorus collection layer contains a composite oxide containing Al and an alkaline earth metal element M.sup.a that includes Mg and that may include at least one selected from the group consisting of Ca, Sr, and Ba, and having a cubic spinel structure belonging to the space group Fd-3m; the composite oxide has a M.sup.a/A1 molar ratio in a range of 0.02 or more and 0.60 or less; and the composite oxide has a peak derived from the cubic spinel structure belonging to the space group Fd-3m of the composite oxide between a diffraction angle 2θxm.sup.ao that is a position of a peak derived from an alkaline earth metal oxide M.sup.aO and a diffraction angle 2θx.sub.Al203 that is a position of a peak derived from an aluminum oxide Al.sub.2O.sub.3 in an X-ray diffraction spectrum.

When the porous ceramic structure contains Co together with Fe or Mn, the Co content is higher than or equal to 0.1 mass % and lower than or equal to 3.0 mass % in terms of Co.sub.3O.sub.4, and when the porous ceramic structure contains Co without containing Fe and Mn, the Co content is higher than or equal to 0.2 mass % and lower than or equal to 6.0 mass % in terms of Co.sub.3O.sub.4. The Ce content is higher than or equal to 0.1 mass % and lower than or equal to 10 mass % in terms of CeO.sub.2. The Fe/Mn/Co ratio is higher than or equal to 0.8 and lower than or equal to 9.5. The content of the metal oxide particles is higher than or equal to 0.3 mass % and lower than or equal to 8.0 mass %.

An exhaust gas purification system of the present disclosure includes a first exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine and a second exhaust gas purification device that additionally purifies the exhaust gas purified by the first exhaust gas purification device, wherein the exhaust gas is exhaust gas with a gaseous composition in which an amount of reducing agents is in excess compared to a stoichiometric gaseous composition and a gaseous composition in which an amount of oxidants is in excess compared to the stoichiometric gaseous composition are alternately switched between, the first exhaust gas purification device includes a three-way catalyst, and the second exhaust gas purification device includes an exhaust gas purification catalyst containing spinel-type MgAl.sub.xFe.sub.2.00−xO.sub.4.00 supporting particles on which Rh is supported, where 0.00<×≤1.50.

An improved catalyst system is provided for the direct decomposition removal of NO.sub.x from an exhaust gas stream at temperatures between about 350° C. and about 600° C. that employs an (amorphous CuO.sub.x)/Co.sub.3O.sub.4 catalyst. The catalyst has an amorphous CuO.sub.x deposit on the surfaces of particles of Co.sub.3O.sub.4 spinel oxide. The catalyst is configured to reduce NO.sub.x to N.sub.2 without the presence of a reductant. The (amorphous CuO.sub.x)/Co.sub.3O.sub.4 catalyst is formed by the precipitation of the deposit from solution onto a suspension of Co.sub.3O.sub.4 spinel oxide particles. The catalyst system can be employed in a catalytic converter for the direct decomposition removal of NO.sub.x from an exhaust gas stream flowing at a temperature of less than or equal to about 500° C.

Catalyst for oxygen storage capacity applications that include a zinc doped manganese-iron spinel mixed oxide material. The zinc doped manganese-iron spinel mixed oxide material may be synthesized by a co-precipitation method using a precipitation agent such as sodium carbonate and exhibits a high oxygen storage capacity.

When the porous ceramic structure contains Co together with Fe or Mn, the Co content is higher than or equal to 0.1 mass % and lower than or equal to 3.0 mass % in terms of Co.sub.3O.sub.4, and when the porous ceramic structure contains Co without containing Fe and Mn, the Co content is higher than or equal to 0.2 mass % and lower than or equal to 6.0 mass % in terms of Co.sub.3O.sub.4. The Ce content is higher than or equal to 0.1 mass % and lower than or equal to 10 mass % in terms of CeO.sub.2. The Fe/Mn/Co ratio is higher than or equal to 0.8 and lower than or equal to 9.5. The porous ceramic structure contains more than or equal to 0.03 percent and less than or equal to 2.5 percent by mass of Zn in terms of ZnO.

When the porous ceramic structure contains Co together with Fe or Mn, the Co content is higher than or equal to 0.1 mass % and lower than or equal to 3.0 mass % in terms of Co.sub.3O.sub.4, and when the porous ceramic structure contains Co without containing Fe and Mn, the Co content is higher than or equal to 0.2 mass % and lower than or equal to 6.0 mass % in terms of Co.sub.3O.sub.4. The Ce content is higher than or equal to 0.1 mass % and lower than or equal to 10 mass % in terms of CeO.sub.2. The Fe/Mn/Co ratio is higher than or equal to 0.8 and lower than or equal to 9.5. The content of the metal oxide particles is higher than or equal to 0.3 mass % and lower than or equal to 8.0 mass %.

A nitrogen oxide storage material comprising: Mg.sub.1−yAl.sub.2O.sub.4−y, wherein y is a number satisfying 0≤y≤0.2, a noble metal, an oxide of a metal other than the noble metal, and a barium compound, the noble metal, the oxide, and the barium compound being loaded on Mg.sub.1−yAl.sub.2O.sub.4−y. The metal oxide comprises at least one metal oxide selected from zirconium oxide, praseodymium oxide, niobium oxide, and iron oxide.

An improved catalyst system is provided for the direct decomposition removal of NO.sub.x from an exhaust gas stream at temperatures between about 350° C. and about 600° C. that employs an (amorphous CuO.sub.x)/Co.sub.3O.sub.4 catalyst. The catalyst has an amorphous CuO.sub.x deposit on the surfaces of particles of Co.sub.3O.sub.4 spinel oxide. The catalyst is configured to reduce NO.sub.x to N.sub.2 without the presence of a reductant. The (amorphous CuO.sub.x)/Co.sub.3O.sub.4 catalyst is formed by the precipitation of the deposit from solution onto a suspension of Co.sub.3O.sub.4 spinel oxide particles. The catalyst system can be employed in a catalytic converter for the direct decomposition removal of NO.sub.x from an exhaust gas stream flowing at a temperature of less than or equal to about 500° C.

There is provided an exhaust gas purification system that allows efficient purification of NOx present in exhaust gas emitted from an internal combustion engine. The exhaust gas purification system of the disclosure comprises a first exhaust gas purification device that purifies exhaust gas emitted from an internal combustion engine, wherein the atmosphere alternately switches between a reducing agent-excess atmosphere and an oxidizing agent-excess atmosphere with respect to the stoichiometric atmosphere, and a second exhaust gas purification device that further purifies the exhaust gas that has been purified by the first exhaust gas purification device, wherein the first exhaust gas purification device has a three-way catalyst, and the second exhaust gas purification device has an exhaust gas purifying catalyst that comprises an AMn.sub.2O.sub.4 spinel-type oxide support (A=Mg, Zn or Li) on which a precious metal is supported.