Carbon-supported copper catalysts I. Characterization

Cu crystallites dispersed on different forms of carbon, i.e., activated carbon, graphitized carbon fibers, and diamond, were prepared and characterized by CO chemisorption, N2O decomposition, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). Both surface and bulk properties of these carbons had an impact on the dispersion as well as the reducibility of Cu. Increasing the concentration of oxygen-containing groups on the surface of the activated carbon by a nitric acid treatment prior to Cu impregnation was beneficial in terms of rendering a higher dispersion of Cu; however, Cu was better stabilized in the higher oxidation states over a high-temperature-treated activated carbon. A higher dispersion of Cu was obtained with the diamond support compared with the graphitized fibers when prepared via a wet impregnation technique, and it is attributed to the stabilization of Cu through interactive "dangling" bonds on the diamond surface. Cu dispersed by an ion-exchange method was stabilized on the graphitized fibers in two morphologically different forms: aggregates of globular particles deposited on top of graphitic basal planes and smaller crystallites at the edges of and at defects within these planes. These morphological differences changed the reducibility of these particles and also may have altered the electronic properties of these crystallites. (C) 1999 Academic Press.