Interface Effects for Cu, CuO, and Cu₂O Deposited on SiO₂ and ZrO₂. XPS Determination of the Valence State of Copper in Cu/SiO₂ and Cu/ZrO₂ Catalysts

TLDR

Experiments with real catalysts emphasize the need for chemical‑state plots that consolidate model‑system data to accurately characterize supported oxide phases. Copper and its oxides were deposited on flat SiO₂ and ZrO₂ substrates by copper evaporation followed by oxidizing treatments. Binding‑energy and Auger‑parameter shifts of several eV were observed as a function of copper or oxide loading and support type, reflecting changes in initial‑ and final‑state effects that can be organized using chemical‑state plots.

Abstract

Copper and copper oxides (Cu2O and CuO) have been deposited by evaporation of copper and subsequent oxidizing treatments, on the surface of flat SiO2 and ZrO2 substrates. Large variations of several eVs have been found in the values of the Cu 2p3/2 binding energy (BE) and Auger parameter (α') of copper as a function of the amount of deposited metallic copper or copper oxides. The magnitude of the changes was also dependent on the type of support upon which the experiment was carried out. These changes have been attributed to modifications in the factors contributing to the initial and final state effects of the process, according to the dispersion degree and the nature of the interactions between the copper oxide moieties and the support. All of these changes can be systematized with the help of chemical state plots. Experiments carried out with real catalysts stress the need of such plots, which summarize the results obtained with the model systems, for a proper characterization of the supported oxide phases in this kind of real materials.