This invention relates to a process for the manufacture of catalysts for the reduction of nitrogen oxides in exhaust gases or for chemical air cleaning processes, in which catalyst moldings are produced from iron oxide or mixtures of iron oxide and chromium oxide and/or manganese oxide, which are reduced to grain sizes less than 2 mm, with the use of inorganic binders and sulfuric acid, and with the possible addition of activating additives.In accordance with the invention:(a) either the mixture of the solid primary material is reacted with sulfuric acid, a mixture of sulfuric acid and phosphoric acid or a sulfuric acid or mixture of sulfuric acid and phosphoric acid containing sulfate, hydrogen sulfate, phosphate or hydrogen phosphate of ammonium, aluminum, iron, vanadium, manganese, molybdenum, chromium, copper and/or cobalt, and moldings are formed from this mixture, or the mixture of the solid primary material is formed into moldings after the addition of fluid and/or phosphoric acid and/or phosphates, and these moldings are treated with sulfuric acid or a sulfuric acid containing sulfate or hydrogen sulfate of ammonium, aluminum, iron, vanadium, manganese, molybdenum, chromium, copper, and(b) then, on the moldings obtained in Step (a), a drying treatment is performed at 110.degree. C. to 250.degree. C., followed by a tempering treatment at 250.degree. C. to 600.degree. C.The catalysts manufactured using the process described by the invention have a low sensitivity to moisture and good activity.