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.

Gangavarapu Ranga Rao

Department Of Chemistry

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Catalysis

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

CeO2-ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV-vis-NIR diffuse reflectance, SEM and acid-base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid-base properties facilitating the dehydrogenation process. At low ceria content, the CeO2-ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)-ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2-ZnO catalysts for reactions involving acid-base sites. © 2005 Elsevier B.V. All rights reserved.

Journal of Molecular Catalysis A: Chemical

Promoting effect of ceria on the physicochemical and catalytic properties of CeO2-ZnO composite oxide catalysts

Surface and catalytic properties of Cu-Ce-O composite materials prepared by solution combustion method have been investigated. The materials are characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR) and electron paramagnetic resonance spectroscopy (EPR). The results of EPR and TPR show finely dispersed Cu2+ species on ceria matrix with low copper content. The Cu2+ species exists in the form of dimers and clusters which are not evident in XRD. In addition CuO is also present as small clusters which grow to larger size at higher Cu content. There is no evidence of CuO forming a solid solution with fluorite CeO2 in combustion method. The Cu2+ species mostly appear on surface rather than in the bulk. Hydrogen peroxide decomposition kinetics has been carried out on Cu-Ce-O composite materials to investigate the effect of crystalline and well-dispersed copper oxide phases on CeO2. From kinetic results, the catalyst materials can be grouped into highly dispersed as well as crystalline CuO phases present on CeO2 matrix. Two parallel compensating lines for dispersed and crystalline CuO phases on CeO2 are observed in ln A versus Ea plot indicating the compensation effect in H2O2 decomposition. This observation is consistent with XRD and EPR results. © 2003 Elsevier Science B.V. All rights reserved.

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Surface and catalytic properties of Cu-Ce-O composite oxides prepared by combustion method

Ce and Al pillared clays were prepared by (i) pillaring Ce3+-exchanged montmorillonite with Al13 polycation (Ce-Al-PILC) and (ii) by pillaring Na-montmorillonite with an oligomer obtained from cohydrolysis of Ce3+ and Al3+ salts (Al-Ce-PILC). Cohydrolyzed oligomer gives larger intercalating species with Ce3+ incorporated in it. The UV-DRS spectrum of clay sample intercalated with this species shows four distinct absorption bands at 224, 263, 294 and 342 nm, which are attributed to the 4f-5d interconfigurational transitions of Ce3+ ions associated with alumina pillars.

Reaction Kinetics and Catalysis Letters

Mixed Al/Ce oxide pillaring of montmorillonite: XRD and UV-VIS diffuse reflectance study

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.

Journal	Journal of Catalysis
Publisher	Academic Press Inc.
ISSN	00219517
Open Access	No