Patent ID: 7906449

Claim:
A selective catalytic reduction type catalyst for purifying nitrogen oxides in exhaust gas exhausted from lean combustion engines using ammonia or urea as a reducing agent, wherein the catalyst comprises a lower-layer catalyst layer (A) having an oxidative function for nitrogen monoxide (NO) in exhaust gas and an upper-layer catalyst layer (B) having an adsorbing function for ammonia on the surface of a monolithic structure type carrier (C), and that the lower-layer catalyst layer (A) comprises the following components of (i), (ii) and (iii), on the other hand, the upper-layer catalyst layer (B) comprises none of the following component (i) but the component (iii): (i) a noble metal being platinum, and content of platinum per unit volume of the monolithic type carrier (C) being 0.05 to 3 g/L; (ii) one or more kinds of oxides selected from alumina, titania, silica, zirconia, tungsten oxide, transition metal oxides, rare earth oxides, or composite oxide thereof, with a content thereof per unit volume of the monolithic type carrier (C) being 5 to 80 g/L; and (iii) zeolite, with the content thereof in the lower-layer catalyst layer (A) per unit volume of the monolithic type carrier (C) being 5 to 80 g/L and the content thereof in the upper-layer catalyst layer (B) per unit volume of the monolithic type carrier (C) being 100 to 160 g/L.