Abstract
Highly non-stoichiometric nanoceria was synthesized for the first time by thermal plasma from the precursor cerium carbonate hydroxide. The particle size was approximately 60 nm according to measurement by TEM. The nanoceria synthesized with 25 kW plasma power with argon as the carrier gas had the largest concentration of oxygen vacancies, follow by that produced with 20 kW with hydrogen as the carrier gas. XRD results indicated that the CeO1.66 phase was present with mostly non-stoichiometric ceria CeO2-x in these two products. SEM and TEM images showed that most of the particles were of irregular shape, while some triangular particles were also present. Raman spectra revealed that the F2g mode of synthesized nanoceria powders had a remarkable downshift of 7.9 - 10.5 cm-1 relative to the peak for single crystal ceria located at 466.0 cm-1. The Raman downshift was explained by the increase in ionic radius upon Ce4+ reduction to Ce3+. XPS results indicated that the Ce3+ content on the surface of the synthesized nanoceria was in the range of 15-30 %, depending on the plasma power and carrier gas composition. Both the Raman and XPS spectra showed numerous oxygen vacancies in the nanoceria. The results of this work indicated that the oxygen vacancy formation occurred when the CeO2 formed from the oxidation of cerium carbonate hydroxide was reduced by the hydrogen as well as the high temperature of the plasma. This investigation has verified that plasma treatment provides a promising method for the synthesis of nanoceria powder with high oxygen vacancies.
Highlights
Cerium has a ground state electron in the 4f orbital (Xe 4f15d16s2), which is responsible for the reduction/oxidation behavior when cycling between its two ionic states, Ce4+, and Ce3+ (Xe 4f1) [1]
X-ray powder diffraction (XRD) results Results of the XRD analysis performed on the product nanoceria are shown in Firstly, CeO2 diffraction peaks (PDF # 04-0593) represent a face-centered cubic structure
Non-stoichiometric nanoceria was successfully synthesized by thermal plasma from cerium carbonate hydrate
Summary
Cerium has a ground state electron in the 4f orbital (Xe 4f15d16s2), which is responsible for the reduction/oxidation behavior when cycling between its two ionic states, Ce4+ (the Xe ground state), and Ce3+ (Xe 4f1) [1]. Ceria has an excellent catalytic activity for converting CO in automobile exhaust gas to CO2 based on its redox property [2]. Ceria is used to produce CO or H2 with solar energy [3]. It is used for chemomechanical polishing and planarization. It has been theorized that the Ce4+ to Ce3+ transition and the presence of surface cerium hydroxyl group are responsible for the catalytic property of ceria [4, 5]. Ceramic materials based on ceria hold much promise for the production of electrolyte for solid oxide fuel cells, and reportedly have a better ion conductance than Y2O3 stabilized ZrO2 (YSZ) [6, 7]
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