Investigation of physicochemical properties and catalytic activity of nanostructured Ce0.7M0.3O2−δ (M = Mn, Fe, Co) solid solutions for CO oxidation

Abstract

In this work, nanosized Ce0.7M0.3O2−δ (M = Mn, Fe, Co) solid solutions were prepared by a facile coprecipitation method and evaluated for CO oxidation. The physicochemical properties of the synthesized samples were investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM and HRTEM, Raman, XPS, and H2-TPR. XRD studies confirmed the formation of nanocrystalline single phase Ce0.7M0.3O2−δ solid solutions. ICP-OES analysis confirmed actual amount of metal loadings in the respective catalysts. The BET surface area of Ce0.7M0.3O2−δ samples significantly enhanced after the incorporation of dopants. TEM studies confirmed nanosized nature of the samples and the average particle sizes of Ce0.7M0.3O2−δ were found to be in the range of ∼8–16 nm. Raman studies indicated that the incorporation of dopant ions into the CeO2 lattice promote the formation of more oxygen vacancies. The existence of oxygen vacancies and different oxidation states (Ce3+/Ce4+ and Mn2+/Mn3+, Fe2+/ Fe3+, and Co2+/Co3+) in the doped CeO2 samples were further confirmed from XPS investigation. TPR measurements revealed an enhanced reducibility of ceria after the incorporation of dopants. The catalytic activity results indicated that the doped CeO2 samples show excellent CO oxidation activity and the order of activity was found to be Ce0.7Mn0.3O2−δ > Ce0.7Fe0.3O2−δ > Ce0.7Co0.3O2−δ > CeO2. The superior CO oxidation performance of CeO2-MnOx has been attributed to a unique Ce-Mn synergistic interaction, which facilitates materials with promoted redox properties and improved oxidation activity.