High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

Abstract

The inverse catalyst ‘cerium oxide (ceria) on copper’ has attracted much interest in recent time because of its promising catalytic activity in the water–gas-shift reaction and the hydrogenation of CO2. For such reactions it is important to study the redox behaviour of this system, in particular with respect to the reduction by H2. Here, we investigate the high-temperature O2 oxidation and H2 reduction of ceria nanoparticles (NPs) and a Cu(111) support by low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). After oxidation at 550 °C, the ceria NPs and the Cu(111) support are fully oxidized, with the copper oxide exhibiting a new oxide structure as verified by LEED and STM. We show that a high H2 dosage in the kilo Langmuir range is needed to entirely reduce the copper support at 550 °C. A work function (WF) difference of △ϕ rCeria/Cu–Cu ≈ −0.6 eV between the ceria NPs and the metallic Cu(111) support is measured, with the Cu(111) surface showing no signatures of separated and confined surface regions composed by an alloy of Cu and Ce. After oxidation, the WF difference is close to zero (△ϕ Ceria/Cu–Cu ≈ −0.1…0 eV), which probably is due to a WF change of both, ceria and copper.