Interaction of Ammonia with Metallic Copper, Nickel and Cobalt Catalysts Studied by Temperature Programmed Desorption

Abstract

AbstractThe adsorption of ammonia on unsupported and alumina supported copper, nickel and cobalt catalysts was studied employing temperature programmed desorption. No ammonia desorption was observed in the experiments carried out with the unsupported metal powders. Nickel and cobalt showed desorption of nitrogen and hydrogen, whereas with copper only nitrogen desorption was observed. On the alumina supported metal catalysts the desorbing gases were ammonia, hydrogen and nitrogen with ammonia as major desorbing species. The investigations indicate that the adsorption of ammonia at 570 K leads to nitride formation on the metal surfaces. The amount of metal nitride formed increases in the sequence: copper, nickel, cobalt. Hydrogen suppresses the nitride formation. This is shown by comparative desorption experiments on catalyst samples which were exposed to hydrogen after exposure to ammonia. The rate of the metal nitride reduction is larger on nickel and cobalt than on copper. This is ascribed to the lower activity of the copper for hydrogen dissociation.