Composition for exhaust gas purification, exhaust gas purifying catalyst containing same, and exhaust gas purifying catalyst structure
A composition for exhaust gas purification including first alumina including alumina containing lanthanum and second alumina including alumina containing lanthanum. The first alumina has a higher lanthanum content than the second alumina. The second alumina has a larger particle size than the first alumina. The lanthanum content of the first alumina is preferably 2 to 12 mass %, in terms of oxide, based on the total mass of alumina and lanthanum oxide of the first alumina. The lanthanum content of the second alumina is preferably 9 mass % or less, in terms of oxide, based on the total mass of alumina and lanthanum oxide of the second alumina.
1. A composition for exhaust gas purification, comprising first alumina comprising alumina containing lanthanum and second alumina comprising alumina containing lanthanum, the first alumina having a higher lanthanum content than the second alumina, and the second alumina having a larger particle size than the first alumina, wherein
the first alumina has a lanthanum content of 2 to 12 mass %, in terms of oxide, based on the total mass of the alumina and lanthanum oxide of the first alumina, and the second alumina has a lanthanum content of 5 mass % or less, in terms of oxide, based on the total mass of the alumina and lanthanum oxide of the second alumina,
the ratio of the lanthanum content Li of the first alumina to the lanthanum content L 2 of the second alumina is 2 to 18, and
the particle size of the first alumina is 2 to 15 μm and the particle size of the second alumina is 20 to 60 μm each size of the first alumina and the second alumina being an arithmetic average of Feret's diameters determined by using a scanning electron microscope.
2. The composition according to claim 1 , wherein a ratio of the particle size of the second alumina to the particle size of the first alumina is 1.5 to 15.
3. The composition according to claim 1 , wherein the mass ratio of the first alumina to the total mass of the first alumina and the second alumina is 20 to 80 mass %, and the mass ratio of the second alumina to the total mass of the first alumina and the second alumina is 80 to 20 mass %.
4. The composition according to claim 1 , wherein the first alumina comprises γ-alumina, and the second alumina comprises θ-alumina.
5. A catalyst for exhaust gas purification, comprising the composition according to claim 1 and a catalyst active component, wherein the catalyst active component is at least one selected from a group consisting of Ag, Mn, Ni, Pt, Pd, Rh, Au, Cu, Fe, Ir, and Co.
6. A catalyst structure for exhaust gas purification, comprising a catalyst substrate, a first catalyst layer formed on one side of the catalyst substrate, and a second catalyst layer formed on a side of the first catalyst layer that is the other side than the side facing to the catalyst substrate, either one of the first catalyst layer or the second catalyst layer or both of the first catalyst layer and the second catalyst layer comprising the catalyst according to claim 5 .
7. A catalyst structure for exhaust gas purification, comprising a catalyst substrate, a first catalyst layer formed on one side of the catalyst substrate, and a second catalyst layer formed on a side of the first catalyst layer that is the other side than the side facing to the catalyst substrate, both of the first catalyst layer and the second catalyst layer comprising the catalyst according to claim 5 .