The present invention relates to a process for preparing a catalyst for the selective catalytic reduction of nitrogen oxide comprising, among other steps, preparing a second aqueous mixture comprising water and an iron salt; and disposing the second mixture on the substrate obtained according to (ii), comprising a coating comprising a zeolitic material comprising copper, over y % of the substrate axial length from the inlet end to the outlet end of the substrate, wherein y is in the range of from 10 to x, obtaining a substrate comprising, in a first zone, the coating comprising a zeolitic material comprising copper and over y % of the substrate axial length an iron salt; and, if x > y, in a second zone extending from y % to x % of the substrate axial length from the inlet end to the outlet end, the coating comprising a zeolitic material comprising copper.