EFFECT OF OXIDATIVE MEDIA ON THE COPPER VALENCE STATE AND SURFACE-COMPOSITION OF A REDUCED COPPER-CHROMIUM-ZINC-ALUMINUM CATALYST

The effect of oxidative treatment on the surface composition and coppe r valence state in a reduced copper-chromium-zinc-aluminum catalyst of the water-gas shift reaction was studied by XPS. The oxidation increa ses the copper content and reduces the carbon concentration on the sur face. A conclusion was made that a part of copper is blocked by carbon on the surface of the reduced catalyst. The copper and carbon concent rations were shown to be a function of the temperature of oxidation an d Cu valence state on the surface. Oxidation of the reduced catalyst, which contains Cu(0) on the surface, increases the copper content due to the copper diffusion from the bulk and, alternatively, zinc and chr omium diffusion into the bulk. The following reduction results in the backward copper diffusion into the volume and zinc and chromium diffus ion from the bulk to the surface. Oxidative-reductive treatment increa ses the total copper content on the catalyst surface.