Gold nanoparticles on ceria supports for the oxidation of carbon monoxide

Ultrafine cubic CeO2 particles were prepared by a solvothermal method, using methanol and different conditions of synthesis, and compared with a commercial CeO2, used as received and after a thermal treatment in nitrogen. The solvothermally prepared materials showed higher specific surface areas (from ∼124 to ∼157 m2/g) than the commercial sample (∼20 m2/g). Au was loaded onto the obtained ceria supports by a double impregnation (DIM) method. Samples were characterised by high-resolution transmission electron microscopy (HTREM), selected area electron diffraction (SAED), energy-dispersive X-ray spectrometry (EDXS), high-angle annular dark-field imaging (HAADF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). Activities for CO oxidation were compared and results were discussed. A gold reference catalyst from the World Gold Council (Type C—Au/Fe2O3) was also used for comparison purposes. Considering the ceria supports alone, the solvothermally prepared samples clearly showed better performance for CO oxidation than the commercial ceria. This can be due to their large amounts of surface oxygen groups, as seen by TPR and TPD, since XRD showed that the same phase was present in all ceria samples. When gold was loaded, full CO conversion was obtained at much lower temperatures. The best results were obtained with the commercial as received sample, which can be explained by the small size of the Au particles (2–5 nm). Other samples (solvothermal) yielded larger Au particle sizes (∼10–30 nm). Although the gold particle size of these solvothermal materials is far from the “ideal” range (below 5 nm), and their activity is consequently lower than that of the commercial ceria, these samples still show better catalytic behaviour in comparison to the reference catalyst. It was shown that Au was in its metallic state when supported in the commercial ceria sample, while a larger contribution from oxidic Au was found in the solvothermal samples.