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Nanocrystalline Ce₁₋ₓSmₓO₂₋δ (x = 0.4) solid solutions: structural characterization versus CO oxidation

Kuntaiah, Kuncham, Sudarsanam, Putla, Reddy, Benjaram M., Vinu, Ajayan
RSC advances 2013 v.3 no.21 pp. 7953-7962
Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, carbon monoxide, catalysts, catalytic activity, cerium, coprecipitation, ions, nanocrystals, oxidation, oxygen, physicochemical properties, samarium, solid solutions, surface area, temperature, transmission electron microscopy
A nanocrystalline Ce–Sm–oxide solid solution, with an excellent redox property and remarkable oxygen storage/release capacity, has been synthesized by means of a simple and highly practicable coprecipitation method. To understand the thermal and textural stability, the synthesized catalyst was subjected to calcination at various temperatures (773–1073 K). Physicochemical characterization was achieved using XRD, HRTEM, BET surface area, Raman, ICP-OES, XPS, TG-TDA, UV-vis DRS, TPR, and FTIR techniques, and the catalytic performance was evaluated for the oxidation of CO. Coprecipitation of Ce⁴⁺ and Sm³⁺ ions through ultra-high dilute solutions provided the single phase Ce₀.₆Sm₀.₄O₂₋δ solid solution in the nanoscale range, as confirmed by XRD and TEM studies. Raman studies revealed two types of lattice defects, namely, oxygen vacancies and MO₈ complex defects due to disparity in the oxidation state and ionic radius of Sm³⁺ and Ce⁴⁺, respectively. Calculations made from XPS atomic ratios (Ce/Sm) and Raman band intensity ratios (AD₁/AF₂g) indicated migration of Sm from the bulk to the surface at elevated temperatures that caused a negative effect on the oxygen vacancy concentration. The doping of Sm³⁺ into the ceria lattice effectively enhanced the reduction behaviour of ceria by shifting the surface and bulk reduction to lower temperatures. Remarkably, Sm-incorporation showed an optimistic influence on the oxygen storage ability and CO oxidation efficiency of ceria attributed to profound lattice defects and enhanced bulk oxygen mobility. The salient features of physicochemical characterization versus catalytic CO oxidation efficiency of Ce–Sm–oxide solid solutions have been elaborated in this article.