Abstract
The redox behaviour of a CuO–CeO 2/Al 2O 3 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 L 3 absorption edges. CuO and CeO 2 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 Cu 2+ cations towards metallic Cu 0. Quick EXAFS spectra taken during reduction show a small amount of intermediate Cu 1+ species. Parallel to the CuO reduction, CeO 2 is also reduced in the same temperature range. About 25% of the Ce 4+ reduces rapidly to Ce 3+ in the 610–640 K temperature interval, while beyond 640 K a further slower reduction of Ce 4+ to Ce 3+ occurs. At 763 K, Ce reduction is still incomplete with 32% of Ce 3+. Re-oxidation of Cu and Ce is fast and brings back the original oxides. The propane reduction of the CuO–CeO 2/Al 2O 3 catalyst involves both CuO and CeO 2 reduction at similar temperatures, which is ascribed to an interaction between the two compounds.
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