LNT layered catalyst for lean burn gasoline engine and exhaust gas purification apparatus using the same

An LNT layered catalyst for a lean burn gasoline engine, comprising a substrate, a first catalyst layer provided on the substrate, and a second catalyst layer provided on the first catalyst layer, wherein

• the first catalyst layer includes ceria-alumina-based base material particles, Pt and Pd supported on the ceria-alumina-based base material particles, and BaO supported on the ceria-alumina-based base material particles, the first catalyst layer having a thickness T,
• the second catalyst layer includes cerin-alumina-based base material particles and Pt and Rh supported on the ceria-alumina-based base material particles,
• a boundary plane positioned between the first catalyst layer and the second catalyst layer, and
• requirements (A) to (D) below are satisfied:
• (A) a content of Pt included in the first catalyst layer is 0.45% to 0.85% by mass, in terms of metal, based on a total solid content of the first catalyst layer,
• (B) a content proportion of Pt in a region ranging from the boundary plane to ⅔ in the thickness T of the first catalyst layer is 88% to 90% by mass based on a total Pt amount included in the first catalyst layer,
• (C) a content proportion of Pt included in a depth region ranging from ⅔ to 3/3 in the thickness direction T of the first catalyst layer with reference to the boundary plane (B) is 10% to 12% by mass based on the total Pt amount included in the first catalyst layer, and
• (D) a content of Ba included in the first catalyst layer is 4% to 11% by mass, in terms of oxide, based on a total amount of the first catalyst layer, and a content of Ba in the second catalyst layer is less than 1% by mass in terms of oxide (BaO) based on the total amount of the second catalyst layer.