Characterization of Ceria-Based Nano-Oxide Catalysts by Raman Spectroscopy

Ceria-based materials have drawn intense research focus due to variety of catalytic and energy related applications. Creation of oxygen vacancy defects imparts oxygen storage and release property (OSC) in the ceria, which facilitates the redox catalytic activity. Introduction of aliovalent dopant ions into the ceria nanocrystals enhances the OSC by generation of extrinsic defects. The current study describes synthesis and characterization of rare earth doped ceria-based mixed oxides. Characterization of the samples was carried out using XRD, BET surface area measurement, TEM, HRTEM, etc. The bulk defect features of the samples were studied employing visible Raman spectroscopy. F2g peak of the Raman spectra evidenced red shift and peak broadening, which could be attributed to change in lattice parameter, oxygen vacancy defects, and smaller crystallite size of the doped nanocrystals. Additional peak (D1) appeared due to the creation of oxygen vacancy defects. The ratio of intensity of D1 peak to F2g peak gave the defect concentration of the doped samples. O 2p and Ce 4f direct band gap energies of the samples were also evaluated. Decrease of band gap energy of the doped samples provided evidence of defect concentration enhancement. A correlation was found among the defect concentration and OSC of the prepared materials. Finally, CO oxidation reaction was performed with the doped materials and the activity was found to be in accordance with the enhancement of defect concentration and OSC.