Redox properties of supported copper catalysts studied in liquid and gas phase by in situ ATR-IR and XAS

The redox behavior of copper-based catalysts plays a prominent role in several important chemical processes. So far relatively little is known about how this behavior is affected by the medium (liquid or gas phase) in which the copper particles are immersed. In this study, we have investigated the redox properties of copper nanoparticles supported on Al2O3, TiO2 and SiO2 in the liquid (presence of solvent) and gas phase by means of in situ Attenuated Total Reflection Infrared spectroscopy (ATR-IR) and in situ X-ray absorption spectroscopy (XAS) in combination with CO adsorption. Using CO and H2 as a reducing agent, the presence of the solvent was found to facilitate reduction of the copper constituent at lower temperatures than in the gas phase. Furthermore, the nature of the support strongly affected the extent of the reduction of the copper constituent. Copper was spontaneously reduced in the presence of CO-saturated solvent to an extent increasing in the order Cu/SiO2 < Cu/Al2O3 < Cu/TiO2. In the gas phase, reduction of the copper constituent in Cu/Al2O3 was more difficult than that in Cu/SiO2. The reduction behavior measured in the presence of the solvent was found to be correlated to the activity of the catalysts in the anaerobic oxidation of 3-octanol.