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

Abstract

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 Ce 4+ and Sm 3+ ions through ultra-high dilute solutions provided the single phase Ce 0.6 Sm 0.4 O 22d 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 MO 8 complex defects due to disparity in the oxidation state and ionic radius of Sm 3+ and Ce 4+ , respectively. Calculations made from XPS atomic ratios (Ce/Sm) and Raman band intensity ratios (A D1 /A F2g) 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 Sm 3+ 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.

Size Controlled Preparation and Effect of Sintering Temperature on the Structural Properties of Nanocrystalline Ceria-Lanthana Solid Solution

“…absorption in the UV region at around 350 nm [1]. This tions from O 2p and Ce 4f orbitals in CeO 2 .…”

“…As compared to bulk materials, nanostructured materials possess enhanced density of defects, due to their larger surface to volume ratio and low co-ordinated surface sites, which promotes a large number of active sites useful for various industrial applications [1][2][3][4][5]. The distinctive catalytic, magnetic and electronic properties of rare earth elements arise due to the 4f orbitals.…”

The Effect of Cerium Oxide Nanoparticle Valence State on Reactive Oxygen Species and Toxicity

“…It is evident that the de-convoluted Ce (3d) spectrum is relatively complex due to the presence of Ce in 3+ and 4+ oxidation states as well as multiple d-splitting. The spin orbit doublets for pure CeO 2 , 3d 3/2 (885.3 and 903.4 eV), and 3d 5/2 (881.9 and 888.6 eV) are clearly evident for both valence states of Ce, indicating that Ce is in mixed valence states of 3+ and 4+ [20]. High-resolution XPS spectra for Ce (3d), the fitted curve, and the corresponding de-convoluted peaks of pure CeO 2 , CeO 2 10 % Gd, and CeO 2 20 % Gd are presented in Fig.…”

Synthesis and application of rare-earth elements (Gd, Sm, and Nd) doped ceria-based solid solutions for methyl mercaptan catalytic decomposition

“…One at lower binding energy, attributed to surface lattice oxygen (O latt ), and another at higher binding energy, originated from surface absorbed oxygen (O ads ) in hydroxyl groups and carbonate species [33]. Usually, when RE ions are incorporated into ceria sample, Ce-O-RE type of bonds are formed, and then the electro-negativity of the guest and host ions vary slightly and the oxygen becomes more labile, which results in the facilitation of migration process from internal lattice oxygen to surface lattice oxygen [13,24]. The results of H 2 -TPR analyses (Fig.…”

“…Hence, detailed lattice defects analyses will be conducted in Raman results that followed. As for the crystallite size (calculated by means of Scherrer equation), it is clear that the addition of RE cation leads to a decrease in the crystallite size of the doped ceria sample, and this may be attributed to the formation of Ce-O-RE bonds which could effectively prevent crystallite from growing [24]. Furthermore, the crystallite size increases with increasing the RE ionic radius from Gd 3+ (Gd 3+ = 1.05 Å) to Sm 3+ (Sm 3+ = 1.08 Å) and then decreases with further increasing the dopant cation size (Nd 3+ = 1.11 Å), and this result is well in agreement with the previous works [20,21].…”