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A storage-reduction type NOx purifying catalyst includes a monolith substrate having formed thereon a coat layer containing a cerium-zirconium composite oxide and a cerium-free oxide, a noble metal and an NOx storing material being supported on the coat layer and the cerium content of the cerium-zir

A storage-reduction type NOx purifying catalyst includes a monolith substrate having formed thereon a coat layer containing a cerium-zirconium composite oxide and a cerium-free oxide, a noble metal and an NOx storing material being supported on the coat layer and the cerium content of the cerium-zirconium composite oxide being less than 30 mol % based on the total molar number of metal atoms contained.

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1. A storage-reduction type NOx purifying catalyst, comprising:a monolithic substrate having formed thereon a coat layer containing a cerium-zirconium composite oxide and a cerium-free oxide, a noble metal and a NOx storing material supported on said coat layer, wherein the cerium content of said ce

1. A storage-reduction type NOx purifying catalyst, comprising:a monolithic substrate having formed thereon a coat layer containing a cerium-zirconium composite oxide and a cerium-free oxide, a noble metal and a NOx storing material supported on said coat layer, wherein the cerium content of said cerium-zirconium composite oxide is less than 30 mol %, based on the total molar number of metal atoms contained. 2. The storage-reduction type NOx purifying catalyst as claimed in claim 1, wherein the cerium content of said cerium-zirconium composite oxide is from 0.1 to 25 mol %, based on the total molar number of metal atoms contained.3. The storage-reduction type NOx purifying catalyst as claimed in claim 1, wherein the cerium content of said cerium-zirconium composite oxide is from 0.5 to 10 mol %, based on the total molar number of metal atoms contained.4. The storage-reduction type NOx purifying catalyst as claimed in claim 1, wherein said cerium-zirconium composite oxide further comprises at least one metal (M) selected from rare earth metals (excluding cerium).5. The storage-reduction type NOx purifying catalyst as claimed in claim 4, wherein said at least one metal (M) selected from rare earth metals is selected from lanthanum, samarium, neodymium, gadolinium and yttrium.6. The storage-reduction type NOx purifying catalyst as claimed in claim 4, wherein the M/Ce molar ratio is from 0.1 to 10.7. The storage-reduction type NOx purifying catalyst as claimed in claim 4, wherein said cerium-zirconium composite oxide contains (Ce+M) in an amount of 10 to 30 mol %, based on the total molar number of metal atoms contained.8. The storage-reduction type NOx purifying catalyst as claimed in claim 1, which comprises a cerium-zirconium composite oxide and a cerium-free oxide at a ratio of 2/8 to 8/2 as a mass ratio of cerium-zirconium composite oxide/cerium-free oxide.9. The storage-reduction type NOx purifying catalyst as claimed in claim 1, wherein said cerium-free oxide is selected from the group consisting of alumina, silica, titania, zirconia, silica-alumina, titania-zirconia and zirconia-calcia.10. The storage-reduction type NOx purifying catalyst as claimed in claim 1, wherein said NOx storing material is at least one member selected from the group consisting of Li, Na, K, Rb, Mg, Ca, Sr and Ba.