Synthesis of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols via peptization at room temperature

A procedure is developed for the synthesis of concentrated CeO₂-ZrO₂ hydrosols based on the peptization of a precipitate obtained by the hydrolysis of a cerium nitrate-zirconium oxynitrate mixture. The time intervals and optimum [H⁺]/[Me ⁿ⁺] molar ratios giving rise the formation of CeO₂-ZrO₂ hydrosols stable to aggregation with a narrow particle size distribution are established. The size, shape, density, and phase composition of the hydrosol particles are determined.     

Synthesis of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols via peptization at elevated temperature

A method for synthesizing aggregation-stable CeO₂-ZrO₂ hydrosols with different particle compositions is developed based on the peptization of hydrated oxide precipitates at elevated temperature. It is shown that, by varying heat treatment time, sols can be obtained with particles that have different degrees of crystallinity and sizes of no larger than 6 nm.     

CO oxidation over Au/CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> catalists: The effect of the support composition of the au-support interaction

The effect of the support composition on the Au-support interactions and its role in the creation of the activity of Au/CeO₂-ZrO₂ catalysts in CO oxidation has been studied. The CeO₂-ZrO₂ oxides and Au/CeO₂-ZrO₂ catalysts were synthesized, characterized by BET, XRD, HRTEM, AAS, TPR-H₂, and tested in CO oxidation. An approximate evaluation of the H₂ consumption for the surface reduction of the studied samples was estimated applying the model developed by Johnson and Mooi, which is based on the qualitative relationship between the amount of the capping oxygen and BET surface area. The sequence of the increasing percentage of O₂ atoms in the capping peak to the total Ce atoms follows the sequence of the decreasing Zr/Ce molar ratio in the sample. The activity of Au/CeO₂-ZrO₂ catalysts depends on the support composition and increases with the decrease in Zr/Ce molar ratio.     

Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide Over ZrO<Subscript>2</Subscript>-based Composite Oxide Catalysts

We have been exploring various new catalyst systems for the utilization of carbon dioxide as a soft oxidant in the catalytic dehydrogenation of ethylbenzene (EB) to styrene. The utilization of CO₂ as a soft oxidant for the commercially important catalytic dehydrogenation of EB to styrene has received enormous attention recently due to its several attractive features. This review summarizes the results of our most recent findings on zirconia-based composite oxide catalyst systems exploited for this reaction. Under this systematic and comprehensive investigation various zirconia-based composite oxide catalysts namely, TiO₂-ZrO₂, MnO₂-ZrO₂, CeO₂-ZrO₂, K₂O/TiO₂-ZrO₂, B₂O₃/TiO₂-ZrO₂ and CeO₂-ZrO₂/SBA-15 have been synthesized, characterized by various techniques and evaluated for the title reaction. Most of these composite oxide catalysts were found to exhibit very interesting physicochemical characteristics and exceptionally better catalytic properties for this reaction. As revealed by characterization results, a large number of acid–base sites with moderate strength are essential for a high conversion and product selectivity of this reaction with CO₂ as the soft oxidant.     

ESR Study of the Formation of O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> Radical Anions on Oxidized CeO<Subscript>2</Subscript> and CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> Adsorbing a CO + O<Subscript>2</Subscript> Mixture

It is demonstrated by ESR measurements that O ₂ ⁻ (CO + O₂) radical anions result from CO + O₂ adsorption on the oxidized surface of CeO₂. These radical anions are stabilized in the coordination sphere of Ce⁴⁺ cations located in isolated and associated anionic vacancies. This reaction shows an activation behavior determined by CO adsorption. The variation of O ₂ ⁻ (CO + O₂) concentration with CO adsorption temperature suggests that surface carbonates and carboxylates participate in this reaction. In the (0.5– 10.0)%CeO₂/ZrO₂ system, O ₂ ⁻ forms on supported CeO₂ and is stabilized on Ce⁴⁺ and Zr⁴⁺ cations. The stability of O ₂ ⁻ -Ce⁴⁺ complexes is lower on supported CeO₂ than on unsupported CeO₂, indicating a strong interaction between the cerium cations and the support.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 423–429.Original Russian Text Copyright © 2005 by Il’ichev, Kuli-zade, Korchak.     

Effects of peak current density on the structure and property of PbO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> nanocomposite electrodes prepared by pulse electrodeposition

PbO₂–CeO₂ nanocomposite electrodes were prepared by pulse electrodeposition method in the lead nitrate solution containing CeO₂ nanoparticles with different peak current density. The content of CeO₂ nanoparticles in the electrodes increase with the increase of peak current density. The effects of peak current density on the morphology and structure of PbO₂–CeO₂ nanocomposite electrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the increase of peak current density can make the morphology finer and more compact, and the crystal size decreases with the increase of peak current density. The oxygen evolution overpotential and stability of PbO₂–CeO₂ nanocomposite electrodes enhance with the increase of peak current density. The electrocatalytic property of PbO₂–CeO₂ nanocomposite electrodes was examined for the electrochemical oxidation of rhodamine B (RhB). The results show that the RhB removal efficiency on PbO₂–CeO₂ nanocomposite electrodes increase with the increase of peak current density, which can be attributed to the higher oxygen evolution overpotential and CeO₂ content in the composite electrodes.     

Three-dimensional hierarchical CeO<Subscript>2</Subscript> nanowalls/TiO<Subscript>2</Subscript> nanofibers heterostructure and its high photocatalytic performance

Combining the versatility of electrospinning technique and hydrothermal growth of nanostructures enabled the fabrication of hierarchical CeO₂/TiO₂ nanofibrous mat. The as-prepared hierarchical heterostructure consisted of CeO₂ nanowalls growing on the primary TiO₂ nanofibers. Interestingly, not only were secondary CeO₂ nanowalls successfully grown on TiO₂ nanofibers substrates, but also the CeO₂ nanowalls were uniformly distributed without aggregation on TiO₂ nanofibers. The photocatalytic studies suggested that the CeO₂/TiO₂ heterostructures showed enhanced photocatalytic efficiency compared with bare TiO₂ nanofibers under UV light irradiation.     

Physicochemical study of composite gel in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> system

We show a feasibility of preparing a highly homogeneous composite gel (CG) based on hydrolysis products of Al₂O₃-ZrO₂ salts. The phase composition of a sample calcined at 1250°C for 2 h is as follows: α-Al₂O₃, t-ZrO₂, and m-ZrO₂ where the t-ZrO₂/m-ZrO₂ phase ratio ranges from 2.8 to 3.8 depending on gel preparation conditions. The investigative tools used are powder X-ray diffraction, differential thermal analysis (atmosphere: Ar), and IR spectroscopy.     

Behavior of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> System at High Temperatures

The system Al₂O₃-ZrO₂ at temperatures of up to 2100°C was studied by differential thermal analysis.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 353–356.Original Russian Text Copyright © 2005 by Kamaev, Archugov, Mikhailov.     

Effect of CeO<Subscript>2</Subscript> and Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> on the phase transformation and optical properties of photostable titanium dioxide

In the present work, the effect of individual additives calculated as molar fractions of Sb₂O₃ and CeO₂ (x _{Sb 2}O₃ range: 0.03–0.08 %, x _{CeO 2} range: 0.05–0.14 %), on the phase composition, phase transformation, and optical properties of photostable rutile titanium dioxide was studied using selective leaching method, ICP-AES technique, XRD method, spectrophotometric analysis and S _BET measurements. The starting material was hydrated titanium dioxide. It was observed that the addition of Sb₂O₃ to TiO₂ did not influence the anatase-rutile phase transformation, but increasing the CeO₂ addition caused a decrease in the rutilization degree. Thus, CeO₂ acted as an inhibitor of the TiO₂ phase transformation. Sb₂O₃ addition to TiO₂ presumably caused the formation of a co-phase of Sb with Ti. Cerium formed a separate phase, CeO₂, and reacted partly with titanium, probably creating co-phase, Ce_0.8Ti_0.2O₂. Comparing the colour of modified rutile titanium dioxide according to the type of the additive introduced, it was found that TiO₂ with CeO₂ had higher brightness but lower white tone values when compared with TiO₂ modified with Sb₂O₃. The relative lightening power and grey tone of the modified TiO₂ were higher in TiO₂ modified with Sb₂O₃. The values of the photocatalytic activity measured in all TiO₂ samples modified either with Sb₂O₃ or CeO₂ were very similar and varied around the value of 21.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Thermal synthesis of the CeO<Subscript>2</Subscript>-PrO<Subscript>2</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>pigments

Summary The synthesis of new compounds based on the CeO₂-PrO₂-Nd₂O₃system, which can be used as pigments for colouring of ceramic glazes, is investigated in our laboratory. The optimum conditions for the syntheses of these compounds have been estimated. The methods of thermal analysis provided first information about the temperature region of the formation of the pigments investigated. The synthesis of these compounds was followed by thermal analysis using STA 449/C Jupiter (Netzsch, Germany).     

Structure and surface properties of ZrO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and Zr<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>2</Subscript> prepared by a microemulsion method according to X-ray diffraction,TPR, and EPR data

It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO₂(m.e.) and CeO₂(m.e.) and the mixed oxide Zr_0.5Ce_0.5O₂(m.e.) in the form of a tetragonal, cubic, and pseudocubic phase, respectively, having crystallite sizes of 5–6 nm. The bond energy of surface oxygen in the (m.e.) samples is lower than in their analogues prepared by pyrolysis. Hydrogen oxidation on the oxides under study occurs at higher temperatures than CO oxidation. ZrO₂(m.e.) and CeO₂(m.e.) are active in O₂⁻ formation during NO + O₂ adsorption, while CeO₂ is active during CO + O₂ adsorption, too. However, its amount here is one-half to one-third its amount in the pyrolysis-prepared samples, signifying a reduced number of active sites, which are Zr⁴⁺ and Ce⁴⁺ coordinatively unsaturated cations and Me⁴⁺-O²⁻ pairs. O₂⁻ radical anions are stabilized in the coordination sphere of Zr⁴⁺ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce⁴⁺ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO₂ phase composition. Zr_0.5Ce_0.5O₂ is inactive in these reactions because of the strong interaction of Zr and Ce cations. It is suggested that Ce^{(4 + β)+} coordinatively unsaturated cations exist on its surface, and their acid strength is lower than that of Zr⁴⁺ and Ce⁴⁺ cations in ZrO₂ and CeO₂, according to the order ZrO₂ > CeO₂ ≥ Zr_0.5Ce_0.5O₂. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide.     

CeO<Subscript>2</Subscript>-catalyzed ozonation of phenol

Three different cerium citrate-based precursors were used for synthesizing CeO₂ through thermal treatment. Three morphological types of CeO₂ were obtained. Characterization of these oxides was carried out by XRD patterns, SEM microscopy, N₂ adsorption isotherms, Raman spectroscopy, zeta potential, and UV/Vis luminescence. Ozonation of phenol catalyzed by CeO₂ was studied as a representative reaction of environmental interest. The differences on the catalytic activity showed by these three oxides could be correlated to amounts of Ce³⁺ on CeO₂ surface and, consequently, to the demand for oxygen needed to burn each precursor.     

Development of CeO<Subscript>2</Subscript>- and TiO<Subscript>2</Subscript>-incorporated aluminium metal-composite matrix with high resistance to corrosion and biofouling

Cerium oxide (CeO₂) is a potential corrosion inhibitor for aluminium, and titanium oxide (TiO₂) is an efficient anti-fouling agent in the marine environment. The present study explored the possibility of incorporating CeO₂ and TiO₂ in aluminium to prepare a metal matrix composite that could have high corrosion and biofouling resistance under marine conditions. Such incorporation of CeO₂ and TiO₂ in pure aluminium offered high resistance to corrosion and biogrowth under marine conditions as evidenced during different tests. The specimens exhibited more anodic and stable open circuit potential throughout the period of the study. The optimum concentration of CeO₂ and TiO₂ was found to be 0.2 and 0.1%, respectively. The present results lay emphasis on the potential scope of the use of CeO₂- and TiO₂-incorporated aluminium in marine environments.     

Effect of cerium dioxide on the properties of monolithic CuO-ZnO-CeO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts in methanol decomposition

Cerium dioxide as a component of CuO-ZnO-CeO₂/Al₂O₃/cordierite catalysts stabilizes their action in the decomposition of methanol by preventing carbon deposition on the surface and facilitating hydrogen formation with selectivity and yield in the range 85–96%. The optimal indices for this reaction are obtained for a CeO₂-CuO/Al₂O₃/cordierite sample prepared using an ammonium precursor for cerium, (NH₄)₂Ce(NO₃)₆. This catalyst displays enhanced reductive capacity relative to the analogous CeO₂-CuO composition prepared using Ce(NO₃)₃·6H₂O.     

The Preparation and Properties of Polyurethane/Nano-CeO<Subscript>2</Subscript> Hybrid Aqueous Coating

To improve the ultraviolet resistance and thermal stability of waterborne polyurethane, stable waterborne polyurethane/nano-cerium oxide hybrid dispersions were obtained by adding nano-cerium colloids to previously synthesized waterborne polyurethane dispersions. The dried ceria colloid was characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The XRD results indicated the prepared CeO₂ was a face-centered cubic structure. The prepared polyurethane/CeO₂ dispersions were studied by dynamic light scattering (DLS), transmission electron microscopy (TEM), UV–Vis spectroscopy and accelerated weathering test. The dried polyurethane/CeO₂ films were characterized using thermogravimetric analysis (TGA). The DLS analysis indicated the particles average diameter of hybrids emulsion was bigger than that of the pure waterborne polyurethane dispersion. TG analysis and accelerated weathering test suggested the hybrid latex films had better thermal stability and mechanical properties than those of the pure waterborne polyurethane. The UV–Vis absorption capacity of the dispersions prepared was increasing with the amount of CeO₂ colloid increased.     

Fabrication of Cu-Doped CeO<Subscript>2</Subscript> Catalysts with Different Dimension Pore Structures for CO Catalytic Oxidation

Transition metal oxides (TMOs) applied as catalysts whose catalytic activities are directly affected by their pores size and pores distributions. Herein, two-dimensional Cu-doped CeO₂ (2D@Cu–CeO₂) and three-dimensional Cu-doped CeO₂ (3D@Cu–CeO₂) were prepared by adopting the mesoporous silica SBA-15 and KIT-6 as templates, respectively. Nanometer Cu-doped CeO₂ (nano@Cu–CeO₂) was synthesized by the method of precipitation. All catalysts were evaluated for the catalytic oxidation of CO, and the 3D@Cu–CeO₂ catalyst exhibited the highest catalytic activity (complete conversion temperature T₁₀₀?=?50?°C), which can be ascribed to the three-dimensional porous channel structure, larger specific surface area and abundant active surface oxygen species. In addition, complete conversion of CO had remained the same after 3D@Cu–CeO₂ was observed for 12 h, indicating it has the best catalytic stability for CO.     

Thermal study of the Ce<Subscript>0.9</Subscript>Tb<Subscript>0.1</Subscript>O<Subscript>2</Subscript> pigment prepared by different synthesis

The inorganic ceramic compounds based on the CeO₂ belong into the group of high-temperature pigments. The pigments have been prepared by the classical dry process (i.e. solid-state reaction) in the temperature range from 1,300 to 1,600 °C and by the coprecipitation at the three different temperatures: 400, 600 and 1,100 °C. The principal of these pigments makes the host lattice of the CeO₂, which is doped by terbium ions. This incorporation of the doped ions leads to obtaining of the interesting dark orange colour after application into ceramic glaze. The aim of our research was to improve and optimize the synthesis conditions of these pigments. The samples were submitted to thermal analysis (TG–DTA) for determination of the temperature interval of the pigment formation and the thermal stability of pigments. The compounds were also measured from the point of view of their colouring, structure and particle size distribution.     

Thermal stability and surface structure of Mo/CeO<Subscript>2</Subscript> and Ce-doped Mo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

In order to explore the influence of CeO₂ on the structure and surface characteristics of molybdena, an investigation was undertaken by using N₂ adsorption (BET method), thermal analysis and in-situ diffuse reflectance infrared (DRIFT) techniques. In this work, the Mo/CeO₂ and Ce-Mo/Al₂O₃ samples were prepared by impregnation and co-precipitation methods with high Mo loadings. Combining the results one may notice that the presence of ceria led to the increase of polymerized surface Mo species so as to forming Mo-O-Ce linkages besides the formation of coupled O=Mo=O bonds indicative of polymeric MoO₃. From thermal analysis, it can be inferred that Mo/Al₂O₃ is the thermally most stable material in the temperature range used in the experiment (up to 900°C), whereas Ce-Mo/Al₂O₃ and Mo/CeO₂ samples undergo morphological modifications above 700°C resulting in lattice defects, which motivate the mobility of Mo and Ce ions and thus enhance the possibility of interaction between them. Additionally, their activity towards CO adsorption needs reduced ceria and molybdena containing coordinatively unsaturated sites (CUS), oxygen vacancies and hydroxyl groups to form various carbonate species.