Characterization of copper cobalt mixed oxide

Samples of CuCo mixed oxide with Cu Co = 0.25 to 1.0 (atomic ratio) were prepared by coprecipitation with Na 2CO 3 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 CuCo 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, CuCo spinel is formed above 588 K and is stable at least up to 623 K for CuCo ≤ 1.0. The thermal stability of CuCo spinel decreases with increasing Cu Co ratio. The electron binding energies of Cu 2p 3 2 , Co 2p 3 2 , and O 1 s are appreciably higher than those in pure CuO and Co 3O 4. This is explanable by the replacement of some Co 3+ ions at octahedral sites of Co 3O 4 spinel by Cu 2+, resulting in a spinel of Co 2+ r Cu 2+ m x Co 3+ n 2− x O 2− 4, with r + m + n = x ≤ 1. The locations of Co 2+, Cu 2+, and Co 3+ ions in the spinel were inferred from their BE assignments, site preference energies, and the Jahn-Teller stabilization of the octahedral d 9 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 CuCo spinel. It was also found that the CuCo spinel-enriched surface has a lower affinity for oxygen species than that of the pure oxides.