Interfacial redox processes under CO/O2 in a nanoceria-supported copper oxide catalyst

A catalyst of copper oxide supported on cerium oxide has been characterized by XRD, Raman, XAFS, XPS, and EPR techniques. Its redox properties under CO/O-2 have been explored with XPS and EPR. The results reveal the presence of mainly CuO-related species highly dispersed over the nanosized ceria support and essentially forming two types of species as a function of their degree of aggregation while isolated Cu2+ cations constitute only a residual part of the copper component. Analysis of the redox processes evidences that reduction starts from interface positions followed by the copper oxide component and extends later to ceria support positions not in contact with the copper oxide. Involvement of each catalyst component in the oxidation processes strongly depends on the starting degree of reduction attained by the system. A simultaneous or sequential, with support oxidation occurring first, oxidation of both oxide components is shown to occur as a function of the initial reduction degree of the system. The sequential mechanism prevails when a relative large reduction degree, leading to stabilization of reduced states of copper, is achieved. A model of the redox processes taking place upon interaction with CO/O-2 is presented on the basis of the results obtained.