Investigation of physicochemical properties and catalytic activity of nanostructured Ce_0.7M_0.3O_2-δ (M = Mn, Fe, Co) solid solutions for CO oxidation

In this work, nanosized Ce_0.7M_0.3O_2-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 Ce_0.7M_0.3O_2-δ solid solutions. ICP-OES analysis confirmed actual amount of metal loadings in the respective catalysts. The BET surface area of Ce_0.7M_0.3O_2-δ samples significantly enhanced after the incorporation of dopants. TEM studies confirmed nanosized nature of the samples and the average particle sizes of Ce_0.7M_0.3O_2-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 Ce_0.7Mn_0.3O_2-δ > Ce_0.7Fe_0.3O_2-δ > Ce_0.7Co_0.3O_2-δ > CeO₂. The superior CO oxidation performance of CeO₂-MnO_x has been attributed to a unique Ce-Mn synergistic interaction, which facilitates materials with promoted redox properties and improved oxidation activity. [Figure not available: see fulltext.]