Carbon-supported copper catalysts I. Characterization

Cu crystallites dispersed on different forms of carbon, i.e., activated car bon, graphitized carbon fibers, and diamond, were prepared and characterize d by CO chemisorption, N2O decomposition, X-ray diffraction, transmission e lectron microscopy, temperature-programmed reduction, and diffuse reflectan ce 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 group s on the surface of the activated carbon by a nitric acid treatment prior t o Cu impregnation was beneficial in terms of rendering a higher dispersion of Cu; however, Cu was better stabilized in the higher oxidation states ove r a high-temperature-treated activated carbon. A higher dispersion of Cu wa s obtained with the diamond support compared with the graphitized fibers wh en prepared via a wet impregnation technique, and it is attributed to the s tabilization of Cu through interactive "dangling" bonds on the diamond surf ace. Cu dispersed by an ion-exchange method was stabilized on the graphitiz ed fibers in two morphologically different forms: aggregates of globular pa rticles deposited on top of graphitic basal planes and smaller crystallites at the edges of and at defects within these planes. These morphological di fferences changed the reducibility of these particles and also may have alt ered the electronic properties of these crystallites. (C) 1999 Academic Pre ss.