| 摘要 |
A catalyst structure for the catalytic reduction of nitrogen oxides contained in an exhaust gas generated by the combustion of a fuel fed under a periodic rich/lean condition, which comprises on an inert substrate (A) a surface catalyst layer containing as the surface catalyst component (a) ceria, (b) praseodymium oxide, or (c) at least one member selected from among mixtures of oxides of at least two elements selected from among cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium, and lanthanum, and double oxides of at least two elements selected from among the same, and (B) an inner catalyst layer containing as the inner catalyst component (a) at least one member selected from among platinum, rhodium, platinum oxides, rhodium oxides and palladium oxides, (b) an NOx absorbent/adsorbent, and (c) a carrier. The above NOx absorbent/adsorbent is an alkali metal compound, an alkaline earth metal compound, a double oxide having magneto-plumbite structure, or a double oxide having perovskite structure.
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