Catalytic oxidation of CO over mesoporous copper-doped ceria catalysts via a facile CTAB-assisted synthesis

Abstract

Nanosized copper-doped ceria CuCe catalysts with a large surface area and well-developed mesoporosity were synthesized by a surfactant-assisted co-precipitation method. The prepared catalysts with different Cu doping concentrations were characterized by XRD, DLS analysis, TEM, BET, Raman, H₂-TPR and in situ DRIFTS techniques. The influence of Cu content on their catalytic performance for CO oxidation was also studied. The XRD results indicate that at a lower content, the Cu partially incorporates into the CeO₂ lattice to form a CuCe solid solution, whereas a higher Cu doping causes the formation of bulk CuO. Copper doping favors an increase in the surface area of the CuCe catalysts and the formation of oxygen vacancies, thereby improving the redox properties. The CuCe samples exhibit higher catalytic performance compared to bare CeO₂ and CuO catalysts. This is ascribed to the synergistic interaction between copper oxide and ceria. In particular, the Cu_0.1Ce catalyst shows the highest catalytic performance (T ₅₀ = 59 °C), as well as excellent stability. The in situ DRIFTS results show that CO adsorbed on surface Cu⁺ (Cu⁺-CO species) can easily react with the active oxygen, while stronger adsorption of carbonate-like species causes catalyst deactivation during the reaction.

Fig. 1. XRD patterns of CuCe catalysts with different CuO contents.

Fig. 2. Particle size distribution of the obtained catalysts.

Fig. 3. TEM images of CeO₂ and Ce_0.1Cu.

Fig. 4. N₂ sorption isotherms (a) and pore size distributions (b) of the CuCe catalysts with different CuO contents.

Fig. 5. Raman spectra recorded at ambient conditions with the obtained samples.

Fig. 6. H₂-TPR profiles of the various CuCe catalysts.

Fig. 7. The catalytic activities of the CuCe catalysts for CO oxidation (a) and stability study of the Cu_0.1Ce catalyst for three successive catalytic cycles (b). Inset: effect of time-on stream on the catalytic activity.

Fig. 8. DRIFTS spectra recorded after exposure to CO on the Cu_0.1Ce sample (a) and CO + O₂ on the Cu_0.1Ce (b) and Cu_0.2Ce (c) samples at different temperatures.

Fig. 9. Influence of pretreatment conditions on the CO conversion.

Fig. 10. The proposed reaction mechanism of CO oxidation over the CuCe catalysts.