An X-Ray Photoelectron Study of Doped and Supported Nickel Oxide

Abstract

The surfaces of lithium-and chromium-doped nickel oxide and of nickel oxide supported on alumina have been examined by X-ray photoelectron spectroscopy. The concentration of the nickel(III) species increased for the lithium-doped oxide and decreased for the chromium-doped oxide relative to the undoped oxide. The effects of doping were manifested most clearly however by the amount of oxygen-containing species adsorbed on the oxide surface rather than by variations in the nickel(III) peak intensity. Lithium-doped oxides were also shown to reduce more readily than undoped or chromium-doped oxides in the presence of carbon-containing impurities. The rate of reduction is influenced by the activation energy for electron transport which is related to the availability of the nickel(III) species. Supported oxides showed significant surface enhancement of nickel(II) as well as an absence of the nickel(III) species. The nickel(II) species in the supported oxide was not easily reduced to nickel(0).