CHARACTERIZATION OF COPPER COBALT MIXED-OXIDE

Samples of CuCo mixed oxide with Cu Co = 0.25 to 1.0 (atomic ratio) were prepared by coprecipitation with Na2CO3 and were characterized with TG, DSC, XRD, and XPS. Exothermic DSC peaks were observed at 588 and 808 K for Cu Co = 0.25, and at 588, 643, and 683 K for Cu Co = 1.0. The formation of CuCo spinel was observed by XRD after calcination of the samples at 623 K, and increased with prolonged heating at this temperature. But calcination at 773 K for 4 hr destroyed the spinel, producing CuO crystallites. Therefore, CuCo spinel is formed above 588 K and is stable at least up to 623 K for CuCo ≤ 1.0. The thermal stability of CuCo spinel decreases with increasing Cu Co ratio. The electron binding energies of Cu 2p 3 2, Co 2p 3 2, and O 1s are appreciably higher than those in pure CuO and Co3O4. This is explanable by the replacement of some Co3+ ions at octahedral sites of Co3O4 spinel by Cu2+, resulting in a spinel of Co2+rCu2+mxCo3+n2-xO2-4, with r + m + n = x ≤ 1. The locations of Co2+, Cu2+, and Co3+ ions in the spinel were inferred from their BE assignments, site preference energies, and the Jahn-Teller stabilization of the octahedral d9 cupric ion. For samples with a bulk Cu Co ration of 0.25, the surface ratio found by XPS is 0.35, while for Cu Co = 1.0, the surface ratio is 0.55, indicating surface enrichment of CuCo spinel. It was also found that the CuCo spinel-enriched surface has a lower affinity for oxygen species than that of the pure oxides. © 1990.