Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces: part 1.—A Fourier-transform infrared study of formic acid and formaldehyde adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

Abstract

Fourier-transform infrared (FTIR) spectra are reported of formic acid and formaldehyde on ZnO/SiO₂, reduced Cu/ZnO/SiO₂ and reoxidised Cu/ZnO/SiO₂ catalyst. Formic acid adsorption on ZnO/SiO₂ produced mainly bidentate zinc formate species with a lesser quantity of unidentate zinc formate. Formic acid on reduced Cu/ZnO/SiO₂ catalyst resulted not only in the formation of bridging copper formate structures but also in an enhanced amount of formate relative to that for ZnO/SiO₂ catalyst. Formic acid on reoxidised Cu/ZnO/SiO₂ gave unidentate formate species on copper in addition to zinc formate moieties.

The interaction of formaldehyde with ZnO/SiO₂ catalyst resulted in the formation of zinc formate species. The same reaction on reduced Cu/ZnO/SiO₂ catalyst gave bridging formate on copper and a remarkable increase in the quantity of formate species associated with the zinc oxide. Adsorption of formaldehyde on a reoxidised Cu/ZnO/SiO₂ catalyst produced bridging copper formate and again an apparent increase in the concentration of zinc formate species. An explanation in terms of the adsorption of molecules at special sites located at the interface between copper and zinc oxide is given.