Nanocomposites and nanomaterials

Influence of the calcination temperature on nanoceria properties 
Grinko A.M.1, Brichka A.V.2, Oranska O.I.2, Bakalinska O.M.2, Kartel M.T.2
1 National University of “Kyiv-Mohyla Academy”. Skovorody Str. 2, Kyiv-04070, Ukraine.
E-mail: alinagrinko2@gmail.com
2 Chuiko Institute of Surface Chemistry, NAS of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine

Cerium oxide nanoparticles are a fascinating material with many applications and more to come. The wide application of CeO2 nanoparticles is associated with its unique redox properties which are related with presence bought Ce3+ and Ce4+ states on the particles surface. The samples synthesis parameters, in particular its calcination, affect it surface chemistry and hence the Ce3+/Ce4+ ratio. The aim of this work is the preparation of nanoceria, calcination it at different temperatures, characterization its properties, and investigate the effect of calcination on catalytic activity of nanoceria in the model reaction of hydrogen decomposition.
Nanoceria was synthesized by reaction of cerium nitrate deposition in an aqueous medium without stabilizers at room temperature. Nano cerium oxide was dried at 20 °C and calcinated in air for 1 hour at 120, 300, 500, 800 °C. SEM images of a samples demonstrate that the morphology of the obtained materials does not significantly change with the increase of the temperature of heat treatment. Energy-dispersive X-ray spectrometry method demonstrated that the O:Ce elements ratio in the samples is in the range 1.7-2.1. X-Ray Diffraction method determined that with increasing calcination temperature, the average size of crystallites and the degree of crystallinity increases. Catalytic activity of nanoceria was studied in the reaction of H2O2 decomposition at different concentration (1-10 %) at room temperature and within pH 8-11. To determine the kinetic data, volumetric method was used. Catalytic activity of the materials was evaluated using the velocity constant. It was shown that dependence of the catalytic activity on pH is extreme with maximum at pH 10. It was found that calcined at 300 °C sample demonstrate highest catalytic activity. We suggest that under this temperature physically adsorbed water molecules are desorbed and catalytic centers became active. Samples heating at higher leads to release from the surface of chemically bounded water molecules and to the oxidation of Ce3+ to Ce4+. As a result, a decreasing in the catalytic activity take place.