Catalysts based on activated aluminum alloys: IV. Unusual valence transitions of copper affected by the reaction medium

It is shown by electron spectroscopy (XPS, Auger electron spectroscopy) that, when copper-containing catalysts prepared by the reaction between activated copper-aluminum alloys and water are reduced by hydrogen, copper is transformed into Cu-0 and Cu1+ states Copper exists in Cu1+ and Cu2+ states in reoxidized samples. Under conditions of oxidation by CO, a portion of Cu2+ ions is reduced to Cu1+. The direct evidence for the formation of strongly reduced copper centers in a CO + air mixture even at an excessive concentration of the oxidant is obtained for the first time, For preliminarily reduced samples, copper is partially oxidized to Cu1+ under the same conditions. A fraction of copper atoms that are transformed to the Cu1+ and Cu-0 states is almost independent of the pretreatment conditions, The action of air or the CO + air mixture on the reduced catalysts results in the redispersion of crystallites of copper oxide or metal.