INVESTIGATION OF ACID-BASE PROPERTIES OF THE SURFACE OF CeO2. NANOPARTICLES SYNTHESIZED BY SOL-GEL METHOD

Abstract

Nano-sized CeO2. was synthesized by the sol-gel method. The optimal conditions for stable CeO2. gels obtaining were determined. The structure and phase composition of the samples were studied by X-ray diffraction. Obtained samples consisted of ceria with face-centered cubic crystal lattice. Acid-base properties of the nano CeO2. surface were investigated by the indicator method. Adsorption of indicators on the surface of oxides allows determining the qualitative composition and concentration of active sites on the oxide surface, and distribution of active sites by the force. Processing of the results based on study of CeO2. samples, calcined at temperatures above 400 °C, allowed identifying the active sites, whose concentration varies significantly with changing the calcination temperature. That was active sites with pKa = 3.8, pKa = 5.2, pKa = 6.4 and pKa = 9.4. For the samples calcined at different temperatures the concentration of basic active sites is higher than the concentration of acid and neutral active sites. When the calcination temperature is below 800°C, mainly the formation of oxygen vacancies occurs due to the removal of oxygen from the surface of CeO2.. Removal of cerium atoms from the surface begins at higher temperatures.

Keywords

• ceo2. nanoparticles, sol-gel method, x-ray analysis, acid-base properties, indicator method