Reduction characteristics of copper oxide in cerium and zirconium oxide systems

The reduction of CuO dispersed on ̄uorite-type oxide catalysts, namely La-doped CeO2 and Y-doped ZrO2 was studied in this work. On both supports distinct copper species were identi®ed as a function of copper content by temperatureprogrammed reduction (TPR) by H2 and CH4, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and scanning transmission electron microscopy/energy dispersive X-ray (STEM/EDX) analyses. At low copper loading (<15 at%), the copper phase is present as small clusters, which are reduced at lower temperature than bulk CuO. At higher Cu loading (>15 at%), in addition to clusters, larger CuO particles are present which are reduced at higher temperature close to the reduction temperature of bulk CuO. At copper loading lower than ca. 5 at%, copper is present as highly dispersed clusters or isolated Cu ions, which interact strongly with the ̄uorite-type oxide, thus requiring higher reduction temperature. However, the latter is still below the bulk CuO reduction temperature. Copper is more stabilized when dispersed in Ce(La)O2 than in Zr(Y)O2 matrix, so that reduction of copper oxide species requires lower temperatures on the Zr(Y)O2-based catalysts. The reducibility of the doped ceria is enhanced by the presence of copper in both H2and CH4-TPR. On the other hand no such interaction is present in CuZr(Y)O2 system. The activity of various copper species for methane oxidation is discussed. # 1998 Elsevier Science B.V. All rights reserved.