Patent ID: 6221324
Filing Date: 2001-04-24
Classification: B01D,B01J,Y02C

Abstract:
A process for the selective catalytic reduction (SCR) of nitrogen oxides using ammonia, comprising using as catalyst a partially copper-exchanged zeolite not generating nitrogen protoxide, said zeolite having a Si/Al ratio of 0.8 to 20,of which the structural arrangement of its SiO.sub.4 and AlO.sub.4 tetrahedra provides both small cavities accessible through windows having 6 tetrahedra and large cavities accessible through windows formed by at least 8 tetrahedra,of which the degree of copper exchange is from 5 to 60%,said zeolite being characterized by two waves of hydrogen consumption in temperature-programmed reduction, the first wave at a temperature below 800.degree. C., the second wave at a temperature above 800.degree. C.,the hydrogen consumption corresponding to the peak of the second wave being substantially equal to half a mole of hydrogen per mole of copper present in said zeolite,the first wave being composed of two peaks P.sub.1 and P.sub.2 resolved by Gaussian deconvolution, the ratio A.sub.1 /A.sub.2 of the areas corresponding to the peaks P.sub.1 and P.sub.2 respectively being greater than 1.5.