Nanosized CeO2–SiO2, CeO2–TiO2, and CeO2–ZrO2 Mixed Oxides: Influence of Supporting Oxide on Thermal Stability and Oxygen Storage Properties of Ceria

Abstract

The influence of SiO 2 , TiO 2 , and ZrO 2 on the structural and redox properties of CeO 2 were systematically investigated by various techniques namely, X-ray diffraction (XRD), Raman spectroscopy (RS), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HREM), BET surface area, and thermogravimetry methods. The effect of supporting oxides on the crystal modification of ceria was also mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahigh dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO 2 -SiO 2 sample primarily consists of nanocrystalline CeO 2 on the amorphous SiO 2 surface. Both crystalline CeO 2 and TiO 2 -anatase phases were noted in the case of CeO 2 -TiO 2 sample. Formation of cubic Ce 0.75 Zr 0.25 O 2 and Ce 0.6 Zr 0.4 O 2 (at 1073 K) were observed in the case of CeO 2 -ZrO 2 sample. The cell 'a' parameter estimations revealed an expansion of the ceria lattice in the case of CeO 2 -TiO 2 , while a contraction is noted in the case of CeO 2 -ZrO 2 . The DRS studies suggest that the supporting oxides significantly influence the band gap energy of CeO 2 . Raman measurements disclose the presence of oxygen vacancies, lattice defects, and displacement of oxide ions from their normal lattice positions in the case of CeO 2 -TiO 2 and CeO 2 -ZrO 2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation states, Si(IV), Ti(IV), and Zr(IV) at the surface of the materials. Cerium is present in both Ce 4+ and Ce 3+ oxidation states. The HREM results reveal well-dispersed CeO 2 nanocrystals over the amorphous SiO 2 matrix in the case of CeO 2 -SiO 2 , isolated CeO 2 and TiO 2 (A) nanocrystals and some overlapping regions in the case of CeO 2 -TiO 2 , and nanosized CeO 2 and Ce-Zr oxides in the case of CeO 2 -ZrO 2 sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO 2 is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of mixed oxides is more than that of pure CeO 2 and the CeO 2 -ZrO 2 exhibits highest OSC.

Enhanced Catalytic Activity of Supported Gold Catalysts for Oxidation of Noxious Environmental Pollutant CO

“…This phenomenon indicates the formation of CZ mixed oxide and the broadness of the spectrum could be due to the presence of smaller crystallite size of ceria which is also established from XRD and BET surface area investigations [32]. In addition, the weak band at around 315 cm −1 represents the displacement of oxygen atoms from their ideal fluorite lattice positions, which shows that CZ sample contains more number of oxygen vacancies [29,32]. Interestingly, no Raman lines due to ZrO 2 could be observed in line with XRD measurements.…”

“…This is again ascribed to the symmetric breathing mode of the oxygen atoms surrounding Ce 4+ cation [27,28]. Moreover, the CZ sample shows one weak band at 598 cm −1 due to nondegenerate longitudinal optical (LO) mode of ceria, which arises due to relaxation of symmetry rules [29]. In particular, this band is correlated with the presence of the oxygen vacancies (O v ) and/or lattice defects (MO 8 -type complex defects).…”

Synthesis of Nanosized Ceria-Zirconia Solid Solutions by a Rapid Microwave-Assisted Combustion Method

“…The average crystallite size of the oxide phases was estimated employing Scherrer equation and considering the XRD data of most prominent line [12]. The lattice parameters were calculated by a standard cubic indexation method using the intensity of the most prominent peak (111) [13]. The N 2 BET surface areas of the powders were determined by N 2 adsorption at liquid nitrogen temperature using a Micromeritics Gemini 2360 instrument.…”

Heteropoly Tungstate Supported on Metal Oxide Catalysts for Liquid Phase Oxidation of Benzyl Alcohol with Hydrogen Peroxide

“…The corresponding reaction process and product optimization were studied by response surface methodology (RSM) and a kinetic model was also established for the alcohol oxidation reaction under optimized conditions. The satisfying catalytic activity observed for the supported HPW/CeO 2 catalysts may be attributed to the unique redox properties and oxygen storage capacity (OSC) [27][28][29][30] as well as the desirable strong acidity and capability of activating oxidant during oxidation of alcohol. 31,32 …”