Redox behaviour of binuclear copper(II) oxide supported on silica

Abstract

The redox behaviour of binuclear copper(II) oxide species supported on silica has been studied on a silica-supported catalyst derived from copper(II) acetate monohydrate containing ca. 50 % binuclear copper oxide species besides dispersed CuO or copper(II) silicate species. For this purpose the reaction of copper(II) oxide species on silica with carbon monoxide or ethanol was carried out, mainly using an e.s.r. or i.r. spectroscopic technique with acetic acid as a probe molecule. Most of the binuclear copper(II) oxide species were reduced with carbon monoxide below 200 °C, followed by the reduction of dispersed CuO up to 300 °C. Copper(II) silicate was not reduced, even at 300 °C. It was also found that the binuclear copper(II) oxide species reacts easily with ethanol to form acetate ions at room temperature. The reoxidation of the sample reduced with carbon monoxide at 300 °C was carried out with oxygen from room temperature to 300 °C. The reduced binuclear copper species was found to be reoxidized even at room temperature. Preadsorbed acetic acid accelerated the reoxidation of the reduced binuclear copper species or dispersed CuO with oxygen at room temperature. The reduction mechanism of the binuclear cupric oxide species on silica is discussed from a structural viewpoint.