Abstract: Hydroxylammonium salts are manufactured by a process comprising the catalytic reduction of nitric oxide with hydrogen in a dilute aqueous solution of a mineral acid in the presence of a suspended platinum catalyst at an elevated temperature, wherein the reaction mixture is recycled and the gas mixture, containing nitric oxide and hydrogen, present in the gas space above the reaction zone, is introduced, by means of one or more downwardly directed jets of liquid, consisting of the recycled reaction mixture and issuing from a nozzle orifice, into one or more circulation zones which are present in the reaction zone, are open at both sides, extend in the direction of the entering jet of liquid and are completely covered by the reaction mixture, the reaction mixture leaving the bottom of the circulation zone and containing unconverted gases is deflected, passed upwards in the annular zone externally surrounding the circulation zone, and at the same time reaction mixture of low gas content is recycled from a separa