THE SURFACE-STATE OF ACTIVE AND INACTIVE CEMENT-SUPPORTED NICKEL-CATALYSTS

Two nickel oxide forms (readily and difficultly reducible) are found b y XPS on the surface of an active NiO/aluminocalcium cement catalyst, whereas only the readily reducible Ni oxide form is present on the sur face of the deactivated catalyst. It is concluded that deactivation oc curs as a result of sufficiently prolonged exposure of the catalyst to .an atmosphere with an oxygen admixture at temperatures below 450-degr ees-C and is associated with destruction of the catalyst cluster struc ture, which provides partial stabilization of NiO in the support matri x. On the surface of catalysts with such a destroyed structure, NiO is fully reduced to the metal state and no Ni0/Ni2+ contact sites could be formed. These sites are responsible for catalytic activity in oxyge n hydrogenation.