Patent ID: 7501105

Claim:
A method for purifying exhaust gas from a diesel engine by selective catalytic reduction, comprising supplying urea into said exhaust gas from a diesel engine, and then bringing said exhaust gas at from 180 to 220° C. into contact with a NOx removal catalyst, said NOx removal catalyst compromising a carrier and ferric oxide supported on said carrier, said carrier comprising a β-zetolite that has undergone ion exchange with iron, wherein an iron ion exchange ratio, represented by a formula (1): [number of mols of iron ions (Fe 3+ ) incorporated within a unit weight of said zeolite by said ion exchange/{(number of mols of Al 2 O 3 incorporated within a unit weight of said zeolite)×(2/3)}]×100 (1) is within a range from 12 to 92%.