In-situ XAS study on the Cu and Ce local structural changes in a CuO–CeO2/Al2O3 catalyst under propane reduction and re-oxidation Original Research Article

The redox behaviour of a CuO–CeO2/Al2O3 catalyst is studied under propane reduction and re-oxidation. The evolution of the local Cu and Ce structure is studied with in-situ transmission X-ray absorption spectroscopy (XAS) at the Cu K and Ce L3 absorption edges. CuO and CeO2 structures are present in the catalyst as such. No structural effect on the local Cu structure is observed upon heating in He up to 873 K or after pre-oxidation at 423 K. Exposure to propane at reaction temperature (600–763 K) fully reduces the Cu2+ cations towards metallic Cu0. Quick EXAFS spectra taken during reduction show a small amount of intermediate Cu1+ species. Parallel to the CuO reduction, CeO2 is also reduced in the same temperature range. About 25% of the Ce4+ reduces rapidly to Ce3+ in the 610–640 K temperature interval, while beyond 640 K a further slower reduction of Ce4+ to Ce3+ occurs. At 763 K, Ce reduction is still incomplete with 32% of Ce3+. Re-oxidation of Cu and Ce is fast and brings back the original oxides. The propane reduction of the CuO–CeO2/Al2O3 catalyst involves both CuO and CeO2 reduction at similar temperatures, which is ascribed to an interaction between the two compounds.