Nanosized Unsupported and Alumina-Supported Ceria-Zirconia and Ceria-Terbia Solid Solutions for CO Oxidation

Abstract

Ceria-zirconia (CZ) and ceria-terbia (CT) and alumina-supported ceria-zirconia (CZA) and ceria-terbia (CTA) solid solutions were synthesized by coprecipitation and deposition precipitation methods, respectively. Structural characteristics and catalytic activity of the synthesized samples have been investigated using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), and Brunauer-Emmett-Teller (BET) surface area measurements. To evaluate the catalytic properties, total oxygen storage capacity and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce 0.75 Zr 0.25 O 2 phase for CZ and Ce 0.5 Zr 0.5 O 2 and Ce 0.6 Zr 0.4 O 2 phases for CZA samples, respectively. While the formation of only Ce 0.8 Tb 0.2 O 2- δ phase was noted for both CT and CTA samples. All the supported and unsupported samples adopted a fluorite-type structure and exhibited cell parameters with respect to Vegard's rule. The HRTEM results indicated well-dispersed particles of the size around 5 nm. The RS measurements suggested the presence of oxygen vacancies due to defective structure formation. The XPS studies revealed the presence of cerium in both Ce 4+ and Ce 3+ oxidation states in different proportions. It was found that CO oxidation for CTA occurs at very much lower temperature than CT, CZ, and CZA samples. Details of these findings by correlating with the structural characterization studies are consolidated. Ceria-zirconia/alumina and ceria-terbia/alumina solid solutions possessing high surface area and thermal stability were synthesized by deposition coprecipitation. Ceria-terbia/alumina has shown better CO oxidation activity due to more number of defects and a high rate of redox cycles.