Aliovalent Metal Ion Doped Ceria Catalysts for CO and Soot Oxidation

Background: Ceria (CeO2) is the focus of constant and diverse research interest due to its wide industrial applications. In particular, ceria-based mixed oxides with nanostructures exhibit better catalytic properties owing to high specific surface area, improved sintering properties and high oxygen storage-release characteristics in comparison to the individual bulk materials. This work is aimed at analyzing the significance of doping in the ceria lattice to enhance CO and soot oxidation activity over a series of CeO2-La2O3, CeO2-Sm2O3, CeO2-Eu2O3 and CeO2-Gd2O3 mixed oxides. Methods: The investigated CeO2 and Ce0.8M0.2O2-δ (M= La, Sm, Eu and Gd) mixed oxides were prepared by a simple and environmental friendly co-precipitation method, characterized in terms of composition, crystalline structure, particle size, hydrogen consumption and oxidation state by the stateof- art techniques, namely, XRD, RS, TEM, TPR, UV-vis DRS, BET SA and OSC and evaluated for CO and soot oxidation reactions. Results: Systematic characterization of the synthesized mixed oxides by various techniques provided interesting information. XRD results confirmed that doped materials exist as single-phase fluorite structured oxides with significant changes in the lattice parameter. Raman spectroscopy results established the presence of oxygen vacancies in various proportions. The incorporation of trivalent cations into the ceria lattice greatly enhanced the OSC of the materials. H2-TPR results confirmed that doped samples are more reducible than pure ceria. Catalytic studies revealed an enhanced activity for both the reactions in contrast to pure ceria. Conclusion: Among various catalysts investigated, the Ce0.8Sm0.2O2-δ combination exhibited better catalytic activity owing to a considerably high OSC and facile reduction at significantly lower temperatures. The catalytic activity results confirmed that CO and soot oxidation activity could be improved by doping the ceria with appropriate trivalent cations.