Patent ID: 8318632

Claim:
An exhaust gas purification catalyst comprising: a substrate, and a first catalyst layer formed on the substrate, the first catalyst layer comprising palladium and/or platinum and alumina doped with an alkaline-earth metal element and having a correlation coefficient ρ Al,AE given by the following formula (1) of 0.75 or more: ρ Al , AE = C Al , AE σ Al ⁢ σ AE ( 1 ) wherein C Al,AE ,σ Al and σ AE in the formula (1) are represented by the following formulae (2), (3) and (4), respectively: C Al , AE = 1 350 ⁢ ∑ i = 1 350 ⁢ ( I Al , i - I Al , av ) ⁢ ( I AE , i - I AE , av ) ( 2 ) σ Al = 1 350 ⁢ ∑ i = 1 350 ⁢ ( I Al , i - I Al , av ) 2 ( 3 ) σ AE = 1 350 ⁢ ∑ i = 1 350 ⁢ ( I AE , i - I AE , av ) 2 ( 4 ) in the formulae (2) to (4), i is a natural number of from 1 to 350, I Al,i is a characteristic X-ray intensity of aluminum that is measured by using an electron beam microanalyzer at the i-th intersection point among 350 intersection points of surfaces that are obtained by dividing the first catalyst layer into 350 equal parts in the thickness direction with a line that is vertical to the main surface of the catalyst layer, I Al,av is an arithmetic average value of the I Al,i given by the following formula (5): I Al , av = 1 350 ⁢ ∑ i = 1 350 ⁢ I Al , i ( 5 ) I AE,i is a characteristic x-ray intensity of the alkaline-earth metal element that is measured by using the electron beam microanalyzer at the i-th intersection point, and I Al,av is an arithmetic average value of the I Al,i given by the following formula (6): I AE , av = 1 350 ⁢ ∑ i = 1 350 ⁢ I AE , i . ( 6 )