Microstructural and spectroscopic investigations of the supported copper alumina oxide system: Nature of aging in oxidizing reaction media

By means of electron microscopy, infrared spectroscopy of adsorbed CO, XPS, and ESR the state of the copper oxide component of the Cu Al O system (CuO/γ-Al 2O 3 and bulk CuAl 2O 4 catalysts) has been investigated. Several types of copper Al oxygen entities were detected on the catalyst surfaces: isolated ions, weak magnetic associates, two- and three-dimensional clusters, defect CuO phase. The dependence of their distribution on composition, preparation, and pretreatment conditions and their reducibility by carbon monoxide have been analyzed. The enthalpy of oxygen adsorption on copper atoms in various structures has been calculated by a semiempirical, interacting-bond method. The most reactive species are three-dimensional clusters reducing to Cu 0 by CO even at 163 K. Prolonged treatment in reaction media (CH 3OH, CH 2O, O 2 at 673–873 K) annealed extended defects in CuO particles and destroyed the clusters, forming perfect CuO particles and bulk aluminate.