A series of ceria-incorporated zirconia (Ce1-xZrxO2, x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard's law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce3+ ← O2- and Ce4+ ← O2- charge transfer transitions. The two vibrational bands in 6960 cm-1 and 5168 cm-1 in the NIR region indicate the presence of surface hydroxyl groups on these materials.

Gangavarapu Ranga Rao

Department Of Chemistry

H. Ranjan Sahu

Cerium

Charge transfer

combustion

Crystal lattices

Crystalline materials

Ultraviolet spectroscopy

X ray diffraction analysis

Zirconia

DIFFUSE REFLECTANCE SPECTROSCOPY (DRS)

VEGARD LAW

Solid solutions

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IIT Madras

XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method

Proceedings of the Indian Academy of Sciences: Chemical Sciences

Advanced synthetic methods under mild and controlled conditions for the synthesis of nanocrystals with specific shapes and exposed surfaces are very important for understanding the surface related properties and to explore their structure-property relationship for various potential applications. Here, we report the synthesis of highly uniform CeO 2 nanorods and nanoflowers in large scale using non-hydrothermal homogeneous precipitation method with urea as a precipitating agent and CTAB as a shape directing agent. Uniform microstructures of CeO 2 samples were selectively synthesized using chloride and nitrate as the counter anions. The samples were characterized by thermal analysis, X-ray diffraction, N 2 adsorption-desorption isotherms, SEM, TEM, UV-Vis-DRS, and Raman spectroscopy, and temperature programmed reduction as well as desorption methods. The results show that the physicochemical and optical properties of CeO 2 samples significantly differ with their surface microstructure and morphology. They also strongly influence the redox property, oxygen storage capacity, and surface acidity of the CeO 2 samples. The CeO 2 samples with different morphologies were tested for their soot oxidation activity. The CeO 2 sample with nanorod morphology was found to be more active due to larger CeO 2/soot interface than the CeO 2 sample with nanoflower morphology. © 2011 Elsevier Inc..

Journal of Colloid and Interface Science

Tuning, via Counter Anions, the Morphology and Catalytic Activity of CeO 2 Prepared under Mild Conditions

The interaction of 20 wt% 12-tungstophosphoric acid with Cex Zr1 - x O2 solid solutions has been studied by PXRD, FTIR, FT-Raman, H2-TPR, NH3-TPD, diffuse reflectance UV-vis-NIR, and 31P MAS NMR techniques. The study indicates that the Keggin anions are attached to Lewis metal ion centres and anion vacancies on Cex Zr1 - x O2 supports through W{double bond, long}O terminal bonds. The Keggin units at the interface are chemically perturbed as indicated by non-intrinsic IR bands observed at 958 cm-1 (W{double bond, long}Oter bond), and 1052, 1102 cm-1 (P{single bond}O bond). NH3-TPD shows that the Keggin anions fixed to Lewis sites and/or oxygen ion vacancies decrease the ammonia uptake on Cex Zr1 - x O2 solid solutions. H2-TPR shows modified redox behaviour of Cex Zr1 - x O2 solid solutions due to the simultaneous reduction of ceria, decomposition of Keggin anions and the reduction of WO3. The broadening of 31P MAS NMR and DR-UV-vis-NIR spectra demonstrate the existence of chemical interactions between the Keggin anions and Cex Zr1 - x O2 supports. © 2008 Elsevier Inc. All rights reserved.

Interaction of Keggin anions of 12-tungstophosphoric acid with Cex Zr1 - x O2 solid solutions

The nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr0.5O2 solid solution has been investigated. The vibrational study shows additional IR features at 1051 and 957 cm-1 which are correlated to the primary Keggin anions interacting with Lewis sites involving Ce4+ and Zr4+ ions, and thus affecting the P-O and W=Oterminal bonds. The IR study indicates the formation of interfacial Ce4+-O-W and Zr4+-O-W bonds. The chemisorbed Keggin molecular layers on Ce0.5Zr0.5O 2 show activity towards conversion of acetophenone to styrene by Meerwein-Ponndorf-Verley reduction followed by dehydration. The activity is correlated with the relative intensities of IR peaks at 1051 and 957 cm -1 of the perturbed Keggin molecular layers. © 2007 Springer Science+Business Media, LLC.

Catalysis Letters

Investigation of 12-tungstophosphoric acid supported on Ce 0.5Zr0.5O2 solid solution

CeO2-ZnO materials were prepared by amorphous citrate process and characterized by TGA, XRD, UV-DRS and surface area measurements. TGA showed that the citrate precursors decompose in the range 350-550°C producing CeO2-containing catalytic materials. XRD and DRS results indicated the formation of well-dispersed interstitial ZnxCe1-2x 4+Ce2x 3+ O2 solid solution on ZnO matrix. Addition of CeO2 to ZnO produced high surface area mixed oxide materials in citrate method. Cyclohexanol conversion reaction was carried out on these catalytic materials to investigate the effect of rare earth oxide on the activity and selectivity. It was found that CeO2 promotes the activity of ZnO without affecting the selectivity to cyclohexanone significantly. The factors such as reaction temperature and WHSV have turned out to be important for cyclohexanol conversion over CeO2-containing ZnO catalyst materials.

Fulltext

Bulletin of Materials Science

Promoting effect of CeO2 on cyclohexanol conversion over CeO2-ZnO mixed oxide materials prepared by amorphous citrate process

With the aim of application for ammonia sensing, zirconium doped ceria (Ce1−xZrxO2for 0 ≤ x ≥ 0.7) nanopowders were synthesized by solution combustion technique using glycine as fuel in stoichiometric ratio. The calcined powders (at 500 °C) were thoroughly characterized by XRD to evaluate how the structural parameters such as lattice constant, crystallite size, cell density, cell volume, strain etc. change with the increase of Zr concentration. The crystallite size is found to reduce from 20 nm to 4 nm with the increase of doping concentration. The strain in crystal, as calculated by William Hall Plots, does not increase with the increase of Zr doping beyond 40 mol%. Micro-Raman study also indicates that beyond 40 mol% doping there exist zirconia phase in the spectra; although XRD could not resolve any segregation evidence. The optical absorption study clearly indicates how the absorption coefficient changes with doping. Incidentally, the band gap is found to reduce (3.15 eV–2.85 eV) with the increase of doping due to dominant doping level transition. In addition to near band edge emission, the photoluminescence emission spectra reveal existence of defect structure with several intra-band transitions within optical band gap. As an active electrode in electrochemical gas sensor, using lanthanum gallate as electrolyte, in amperometric mode, the synthesized Zr doped ceria was found to be highly sensitive to detect ammonia gas down to 3 ppm level in the temperature range 300–450 °C. © 2016 Elsevier B.V.

Journal of Alloys and Compounds

Structural analysis of Zr4+ doped ceria, a possible material for ammonia detection in ppm level

Fine powders of zirconia were prepared by employing combustion method with varying fuel to precursor molar ratios. The zirconia powders contained more amount of monoclinic phase as the fuel content was increased. This aspect was studied using XRD, IR and UV-vis diffuse reflectance techniques. The surface acid-base properties of these samples were also investigated by indicator titration method. The catalytic activity was probed with transfer hydrogenation reaction in liquid phase. It was found that combustion synthesized zirconia did not provide required active sites for transfer hydrogenation reactions in liquid phase unlike hydrous zirconia.

Characterization of combustion synthesized zirconia powder by UV-vis, IR and other techniques

Reduction of NO by CO catalysed by Rh/CeO2-ZrO2 solid solutions is investigated with the aim to elucidate the role of the CeO2-ZrO2 supports in modifying the activity of supported Rh. Two distinct kinetic regimes, characterised by different activation energies are observed below and above 500 K. It is proposed that below 500 K the reduction of NO occurs at the expenses of a concomitant oxidation of Ce3+ sites. In this model, the supported metal activates the reducing agent favouring the efficiency of Ce4+/Ce3+ redox couple. The influence of a high temperature reduction (H2, 1073 K) is also investigated. Such a treatment, which increases the reducibility at low temperatures of the CeO2-ZrO2 solid solution, promotes the efficiency of the catalysts at low temperatures, confirming the important role of the Ce4+/Ce3+ redox couple in determining the activity of the catalyst. © 1998 Academic Press.

Journal of Catalysis

Reduction of NO by CO over Rh/CeO2-ZrO2 catalysts: Evidence for a support-promoted catalytic activity

Langmuir

Preparation and Physicochemical Properties of ZrO2and Fe/ZrO2Prepared by a Sol−Gel Technique

Ionic Dispersion of Pt and Pd on CeO2 by Combustion Method: Effect of Metal–Ceria Interaction on Catalytic Activities for NO Reduction and CO and Hydrocarbon Oxidation

Chemistry of Materials

Electron Paramagnetic Resonance in Combination with the Thermal Analysis, X-ray Diffraction, and Raman Spectroscopy to Follow the Structural Properties of ZrxCe1-xO2Solid Systems and Precursors

Journal	Proceedings of the Indian Academy of Sciences: Chemical Sciences
Publisher	Indian Academy of Sciences
ISSN	02534134
Open Access	No