Cerium-zirconium oxides

Cerium oxide, 74 649, 650 air/fuel conditions and, 70 50 for oxidizing iron in glass, 7 343 energy gap at room temperature, 5 596t Cerium(III) oxysulfide, 5 677 Cerium(III) phosphate, 5 677 Cerium sesquioxide, 5 675 Cerium(III) sulfide, 5 676 Cerium tetrachloride, 5 674 Cerium-zirconium oxides, 74 649 Cerius2 software, 7 629 7 385, 399, 422 76 754... 

A complete range of metastable cerium-zirconium mixed metal oxide powders (CexZr(i.x)Oy, 0 < X < 1) were prepared through a similar hydroxide precipitation technique reported by Hori, et al. [11]. Cerium (IV) ammonium nitrate and zirconium oxynitrate precursors are completely dissolved in de-ionized water with mild heat and precipitated through the addition of excess ammonium hydroxide (-100 vol%). The ceria-zirconia is thoroughly washed with excess distilled water and allowed to evaporate to dryness overnight. The ceria-zirconia system is calcined in atmosphere for 1 hour at 773 K and subsequently milled into a fine powder. The model ceria-zirconia catalysts are prepared from the ground cerium-zirconium oxide powders using a 13 mm diameter pellet die and hydraulic press. 

Transition metal oxides that do not change their transparency, or color very little, under ion/electron insertion and extraction can also be used as a counter electrode in electrochromic devices anploying tungsten oxide as a cathodic material. There has been particular interest in oxides based on vanadium pentoxide and cerium oxide. Pure V2O5 as well as a mixture of vanadium and titanium oxide are of interest. Cerium-based mixed oxides, in particular cerium-zirconium oxide (Veszelei et al. [1999]), exhibit less optical absorption, but the stability is not sufficient for many applications. 

Determination of cerium as cerium(IV) iodate and subsequent ignition to cerium(IV) oxide Discussion. Cerium may be determined as cerium(IV) iodate, Ce(I03)4, which is ignited to and weighed as the oxide, Ce02. Thorium (also titanium and zirconium) must, however, be first removed (see Section 11.44) the method is then applicable in the presence of relatively large quantities of lanthanides. Titrimetric methods (see Section 10.104 to Section 10.109) are generally preferred. 

Selected OSC values are reported in Table 8.1 for ceria and cerium-zirconium mixed oxides. These results confirm that the isomorphous substitution of Ce4+ by Zr4+ ions clearly improves the catalyst stability. BET (Brunauer, Emmett, Teller) area of ceria treated at 900°C is close to 20m2g 1 while it amounts to 35 15 m2g 1 for most mixed... 

L. Kundakovic, and M. Rytzani-Stephanopoulos, Reduction characterization of copper oxide in cerium and zirconium oxide systems, Appl. Catal. A Gen. 171, 13—29 (1998). 

The OSC at 400 C of this series of cerium-zirconium mixed oxides pre-calcined at 900X was measured. Fig. 7.2 represents the variations of the OSC vs. cerium content. 

Additional measurements on a full series of ceria and cerium-zirconium mixed oxides supported noble metals showed that Ru was at least 10000 times more active than Pd and about 20 times more active than Rh for the activation of oxygen [70]. Up to now, most results were obtained with Rh catalysts but Ru could be a good candidate for surface diffusion measurements. 

Special Refractories.— Under certain conditions refractories of special qualities may be employed such as zirconium oxide, zirconium silicate, chromite, fused silica, boron nitride, aluminum nitride, lime, beryllium oxide, cerium dioxide, thoria, asbestos and various synthetic combinations. 

Mesoporous yttrium zirconium oxide or mesoporous cerium oxide anodes and a mesoporous lanthanum strontium manganate cathode constructed from nanocrystallites of these materials organized by a templating mesophase can be used in solid-oxide fuel cells. Mesoporous TiCU has a potential application in dye-sensitized solar cells. 

All BET surface areas are reported in Fig. 5. Whatever the series, introduction of Pr results in a decrease of the BET surface area. For series 1 samples, this decrease is even more pronounced for x > 0.5. It seems that the presence of Pr60u could be responsible for this decrease of surface area. Furthermore, the presence of zirconium remains crucial to stabilize cerium-praseodymium oxides BET surface areas of series 1 samples are much higher than those of series 2, except for x = 1. Praseodymium can stabilize the texture of ceria but its influence in obtaining high surface area oxides appears to be much weaker than in the case of zirconium addition. [2-4, 16]... 

Two different cerium oxide promoted zirconias were prepared and tested as supports for Pd catalysts for the catalytic oxidation of methane, alone and in presence of a strong catalyst poison (SO2). The introduction of cerium oxide was carried out by incipient wetness of zirconium hydroxide or zirconium oxide, followed by calcination. Both catalysts present very different properties, the first method producing a catalyst with better performance, and thermal stability markedly higher than the unmodified zirconia support. However, the addition of cerium does not lead to any enhancement of the catalyst performance in presence ofSC>2,... 

Cerium was added to the support by two different procedures, both based in the incipient wetness method. In the first procedure, zirconium hydroxide was impregnated with aqueous cerium (IV) nitrate in order to get 1 % wt of cerium in the support (support A). The second procedure consisted of calcining the hydroxide at 700 C for 4 h to obtain the oxide and then impregnation with the same cerium solution (support B). In both cases the incipient wetness technique was used to impregnate the solid. Zirconium oxide with no cerium added was prepared by calcining the hydroxide at 700 C. 

A marked influence of the procedure for the addition of cerium was observed in XRD profiles. These profiles suggest that the proportion of zirconium oxide with tetragonal structure, considered as the most stable phase, is higher for procedure A. Important changes with respect to unmodified zirconia were not observed in the case of procedure B. No cerium-containing phases were detected, probably because of the low cerium content of the catalysts. 

The chemical composition of the washcoat belongs to the core know-how of the catalyst manufacturers. The most common washcoats contain aluminum oxides, cerium oxides and zirconium oxides as major constituents. The minor constituents... 

Nowadays, some of the washcoat internal surface area is provided by cerium and zirconium oxides. Those oxides are available in a modification that exhibits a moderately high internal surface area, typically 20-100m g , together with an appreciable stability of this internal surface area at typical catalyst operating temperatures. 

Zirconium oxides are the preferred supports for the precious metal component rhodium. The cerium oxide and/or the zirconium oxide are added to the washcoat either as preformed oxides or as oxide precursors, such as their respective carbonates or nitrates - the oxides are then formed in situ during washcoat drying and calcination. 

The cerium-zirconium mixed oxide (Ce/Zr = 64/36, atomic ratio) as well as the pure ceria samples (both without and with Pt) were obtained by a Rhone-Poulenc proprietary process. The purity of the cerium used was higher than 99.5%. For the study of the interaction between Pt and cerium-zirconium mixed oxides, a hexachloroplatinic solution was used as a source of Pt. The OH groups on the surface of the mixed oxides were exchanged by PtCle ions in water. The material obtained was dried in an oven at 120°C and calcined in a muffle furnace at 500°C. For aged catalysts, the calcination was performed at 900°C for 6 hours. The Pt loading was 0.5% (weight %). 

A key was the development of more thermally stable forms of cerium oxide. Unstabilized cerium oxide degrades rapidly at exhaust temperatures in excess of 800° C, and this degradation significantly reduces the efficiency of the catalyst for NO-N02 reduction. Greater thermal stability was achieved by forming solid solutions of stabilizers such as zirconium oxide and lanthanum oxide in cerium oxide. Hence, these new materials are the most significant enablers for the lower NO-N02 standards required for 2004 and beyond. 

Modify the electrodes in the cerium (or zirconium) oxide devices to detect CO in the presence of hydrogen. 

By impregnating y-Al203 with cerium/zirconium citrate solutions and subsequent calcination nanostructured CemZri.n,02 mixed oxides supported on AI2O3 are obtained, which feature remarkably high oxygen stor e even after a calcination at 1373 K for 24 h. Mutual thermal stabilisation between alumina and solid solutions has been observed, which prevents formation of a-alumina and sintering effects after a severe ageing. 

An Auger Electron Spectroscopy Study of SO2 Adsorption on Cerium-Zirconium Mixed Metal Oxides... 

Cerium-zirconium mixed metal oxides are used in conjunction with platinum group metals to reduce and eliminate pollutants in automotive emissions control catalyst systems. The ceria-zirconia promoter materials regulate the partial pressure of oxygen near the catalyst surface, thereby facilitating catalytic oxidation and reduction of gas phase pollutants. However, ceria-zirconia is particularly susceptible to chemical and physical deactivation through sulfur dioxide adsorption. The interaction of sulfur dioxide with ceria-zirconia model catalysts has been studied with Auger spectroscopy to develop fundamental information regarding the sulfur dioxide deactivation mechanism. 

MPa for a duration in excess of 10 minutes. The prepared wafers have a thickness of approximately 100 to 150 pm, depending on the initial quantity of oxide power used. The systems were thoroughly characterized with several spectroscopic techniques [12,13] to ensure accurate compositional and morphological information. The cerium-zirconium model catalysts were studied to facilitate sulfur deactivation characterization. 

Complex FCC oxides of the fluorite type represent oxygen-conduction solid electrolytes (SOE s). They comprise a typical class of materials for the manufacture of sensors of oxygen activity in complex gas mixtures, oxygen pumps, electrolyzers and high-temperature fuel elements. These materials are based on doped oxides of cerium and thorium, zirconium and hafnium, and bismuth oxide. Materials based on zirconium oxide, for example, yttrium stabilized zirconia (YSZ) are the most known and studied among them. This fact is explained both by their processibility and a wide spectrum of practical applications and by the possibility to conduct studies on single crystals, which have the commercial name "fianites" and are used in jewelry. 

The Nemst glower is a cylindrical bar composed of zirconium oxide, cerium oxide, and thorium oxide that is heated electrically to a temperature between 1500 and 2000 K. The source is generally about 20 mm long and 2 mm in diameter. The rare earth oxide ceramic is an electrical resistor passing current through it causes it to heat and glow. 

If those particles had been of moderate solubility, like the calcium phosphate, iron oxide, or zinc oxide particles, they would have been suspended sufficiendy long to be dissolved. Alternatively, if they had been nearly insoluble, as were the titanium oxide, cerium oxide, and zirconium oxide particles, we would expect them to persist. Thus, the particles could either dissolve direcdy or persist as insoluble particles. Previous work with titanium dioxide has shown it to be virtually insoluble in vitro and to persist in vivo. 

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