Exhaust gas purifying catalyst

1. An exhaust gas purifying catalyst which is disposed in an exhaust pipe of an internal combustion engine, the exhaust gas purifying catalyst comprising:

a substrate; and

a catalyst layer, supported in the substrate and including:

noble metals including platinum (Pt) and palladium (Pd);

a heat-resistant inorganic oxide; and

a NOx trapping material, wherein

the exhaust gas purifying catalyst adsorbs NOx in an exhaust gas when an exhaust air-fuel ratio is in a lean state and desorbs and reduces the adsorbed NOx when the exhaust air-fuel ratio is in a stoichiometric state or a rich state, and

(Pt/Pd) which is a ratio of amount of the platinum (Pt) to amount of the palladium (Pd) is 0.7 or more and less than 1.0.

2. The exhaust gas purifying catalyst according to claim 1 , wherein

the NOx trapping material is an alkaline metal or an alkaline earth metal.

3. The exhaust gas purifying catalyst according to claim 2 , wherein

the alkaline metal or the alkaline earth metal is potassium (K).

4. The exhaust gas purifying catalyst according to claim 1 , wherein

the internal combustion engine is a direct injection type internal combustion engine in which fuel is injected directly in a combustion chamber for lean burning, and

a three-way catalyst is disposed downstream of the exhaust gas purifying catalyst.

5. The exhaust gas purifying catalyst according to claim 1 , wherein

The substrate is made of metal and has corner portions of an acute angle in an interior of a cell thereof, and

minute pores are formed in the catalyst layer supported on the corner portions.