Structure of the catalytically active copper-ceria interfacial perimeter

Cu/CeO2 catalysts are highly active for the low-temperature water-gas shift-a core reaction in syngas chemistry for tuning the H-2/CO/CO2 proportions in feed streams-but the direct identification and quantitative description of the active sites remain challenging. Here we report that the active copper clusters consist of a bottom layer of mainly Cu+ atoms bonded on the oxygen vacancies (O-v) of ceria, in a form of Cu+-O-v-Ce3+, and a top layer of Cu-0 atoms coordinated with the underlying Cu+ atoms. This atomic structure model is based on directly observing copper clusters dispersed on ceria by a combination of scanning transmission electron microscopy and electron energy loss spectroscopy, in situ probing of the interfacial copper-ceria bonding environment by infrared spectroscopy and rationalization by density functional theory calculations. These results, together with reaction kinetics, reveal that the reaction occurs at the copper-ceria interfacial perimeter via a site cooperation mechanism: the Cu+ site chemically adsorbs CO whereas the neighbouring O-v-Ce3+ site dissociatively activates H2O.