Abstract: The use of mixed-oxides containing CeO2 as oxygen storage/release components is discussed with special focus on the applications of these materials in auto-exhaust catalytic converters. Ceria easily forms solid solutions with transition-metal/rare-earth oxides over a wide composition range. The incorporation of dopants like Zr4+, Pr3/4+, Tb3/4+ into the cubic fluorite lattice of CeO2 strongly affects the structural and energetic properties of the materials by lowering activation energy for oxygen migration and by increasing reducibility of the cerium cation. This augments both total and kinetic oxygen exchange between the solid and the gas phase under conditions typically encountered in real systems.

Abstract: AZ r-Ce mixed oxide with ca. a 1:1 atomic ratio is prepared by a microemulsion method and studied by X-ray diffraction, transmission electron microscopy, and Raman, X-ray photoelectron (XPS) and electron paramagnetic resonance (EPR) spectroscopies. The results show the formation of a high surface area material (SBET ) 96 m2 g-1) constituted by homodispersed particles of a major pseudocubic phase t′′ (as shown by Raman); the stabilization of the latter phase, instead of the normally more stable tetragonal phase t′, is probably due to the small crystallite size (ca. 5 nm). XPS indicates a moderate degree of surface enrichment in cerium. An EPR study is carried out on the superoxide species formed on the material by O2 adsorption after outgassing at temperatures up to Tv ) 773 K; this shows that the reduced surface centers thermally formed on this mixed oxide are similar to those found on pure ceria but are generated more easily than on the latter, thus evidencing a surface redox reactivity higher than that of the CeO2 single oxide.

Abstract: Metal containing hydrotalcites, where metal oxides present redox properties and hydrotalcite shows a basic character, appear to be new important environmental catalysts for the removal of SOx and NOx. Redox and basic properties of a mixed Co/Mg/Al oxide derived from hydrotalcites are tuned in order to achieve the optimal catalytic behavior required. This sample has been characterized showing that cobalt is present in two forms, as isolated and well dispersed paramagnetic ions, and as very small Co-containing particles (in the nanometric range), with an internal antiferromagnetic ordering at low temperature. The redox properties of cobalt allow the reduction of NO with propane at high temperatures and in presence of oxygen. The reduced cobalt species are proposed as the active sites. Nevertheless, for the removal of SO2 and contrary to the case of Cu/Mg/Al samples, the addition of an oxidant as cerium oxide on Co/Mg/Al is necessary in order to oxidize SO2 to SO3. In this case, similar results than those obtained with previously reported catalyst, i.e. cerium or copper–cerium hydrotalcite, are obtained. These results indicate that this catalyst could be an adequate material for the simultaneous removal of SO2 and NOx in a FCC unit.

Abstract: The catalytic activity of several cerium/zirconium mixed oxides for TWC applications has been investigated with the aim of optimising the Ce/Zr composition. Their catalytic activity was surprisingly high, considering that no noble metal was present in the composition, particularly for oxidation reactions (CO and C3H6), while their reduction activity was very small (NO). The specific activity of the mixed oxides for CO and C3H6 was found to be the contribution of the individual specific activity of the single oxides. The best activity in practice (lowest T0 and T50 and highest X773) was found for the mixed oxide with a Ce/Zr ratio of 80/20, as a combination of its high specific activity and the highest specific surface area.

Abstract: A catalytic converter for cleaning exhaust gas includes a heat-resistant support, and a catalytic coating formed on the heat-resistant support. The catalytic coating contains Pd-carrying particles of a cerium complex oxide, Pt & Rh-carrying particles of zirconium complex oxide, and particles of a heat-resistant inorganic oxide.

Abstract: The stability of the trivalent state in the lanthanides1 is exploited in the use of SmI2 as a reducing agent,2 and also in the use of [(NH4)2][Ce(NO3)6] (CAN) as an oxidizing agent.3 Cerium is the only lanthanide for which the tetravalent state is readily attained in solution, although in view of the high oxidizing potential of this ion [E°(CeIV/III): 1.7 V (1 M HClO4)] its stability in water must be due to kinetic factors.4 The organometallic chemistry of cerium(IV) is correspondingly sparse5 and it has recently been confirmed experimentally6 that cerocene [Ce(η8C8H8)2] and its analogues7 are best described as [Ce3+{(η8C8H8)2}], i.e. containing cerium(III). We note that in the actinide complexes of the triamidoamines8 [N(CH2CH2NR)3] (particularly the ligand with R ) SiMe2Bu, henceforth NN′3) the higher oxidation states in the metal are stabilized.9 Here we report that as a consequence of exceptionally high Lewis acidity at the metal, cerium(IV) triamidoamines are unusually stable to reduction, even in the presence of an iodide ligand. The solvent-base free trivalent complex [Ce(NN′3)] (1) was readily synthesized (Scheme 1) by a method similar to that which we have used to prepare the group 3 complexes,10 i.e. treatment of [CeCl3(THF)4] with [Li3(THF)3(NN′3)] in dry THF followed by sublimation in vacuo. This bright yellow-orange complex decomposes rapidly in air but is otherwise quite stable.12 The reaction of 1 as a solution in pentane with 0.5-1.5 equiv of chlorine led to an immediate color change to purple and deposition of large purple crystals of the fascinating mixed valence CeIII/IV complex [{Ce(NN′3)}2(μ-Cl)] (2). Similarly, reaction of 1 with bromine gave purple [{Ce(NN′3)}2(μ-Br)] (3). Most unexpectedly, however, the weakest oxidizing agent iodine gave the purple cerium(IV) iodide complex, [Ce(NN′3)I] (4). The molecular structures of 2 (Figure 1) and 313 are analogous to those of the uranium complex [{U(NN′3)}2(μ-Cl)] which we have synthesized by reduction of [U(NN′3)Cl] with potassium.9d The presence of a crystallographic inversion center that coincides with the apparent position of the halogen atoms in the structures of 2 and 3 requires that the two 3-fold symmetric (triamidoamine)cerium fragments are crystallographically equivalent. The anisotropic displacement ellipsoid for the Cl atom in 2 has its greatest amplitude along the Ce-Cl-Ce vector, i.e. at right angles to the expected maximum thermal libration. This is consistent with the presence in 2 and 3 of unsymmetric Ce-X f Ce bridges with the halogen atom disordered between two positions on the intermetallic axis. Although the molecular structure of the triamidoamine fragment in 4 (Figure 2) is unexceptional,9,10 the CeIV-I unit [3.1284(6) A] is without precedent. Known CeIII-I distances range from 3.157(1) A in [CeI3(HOPr)3] to 3.299(1) A in [Ce(η-C8H8)I(THF)3].

Abstract: A rare earth permanent magnet alloy having a composition expressed as RxF?100-(x+y+z+m+n)?ByTzMmDn. In this formula, R is one or more of rare earthy elements, such as neodymium, lanthanum, cerium, dysprosium and/or praseodymium; F is Fe or Fe and up to 20 atomic percent of Co by substitution; B is boron; T is one or more elements selected from the group of Ti, Zr, Cr, Mn, Hf, Nb, V, Mo, W and Ta; M is one or more elements selected from the group of Si, Al, Ge, Ga, Cu, Ag, and Au; and D is one or more elements selected from the group of C, N, P, and O. In this formula, x, y, z, m, n are atomic percentages in the ranges of 3∫x∫15, 4∫y∫22, 0.5∫z∫5, 0.1∫m∫2, and 0.1∫n∫4. Fine amorphous particles of such alloy are made by atomization and/or splat-quenching. Both substantially-spherical, irregular and substantially plate-like particles are simultaneously produced.

Abstract: The present invention concerns a method of growing a cerium-doped SrS phosphor layer by the Atomic Layer Epitaxy-method. According to the invention an organometallic cerium compound containing at least one cyclopentadienyl type ligand is used as a precursor for the dopant cerium. The cyclopentadienyl type cerium compounds can be used as ALE precursors at about 400° C. substrate temperatures without any observable thermal decomposition during processing.

Abstract: The destructive adsorption of CCl4 on La2O3 and CeO2 in the absence of any oxidant, such as oxygen, has been studied by X-ray photoelectron spectroscopy and insitu Raman spectroscopy as a function of the reaction temperature and the amount of CCl4 injected. La2O3 was much more reactive than CeO2, and CCl4 destruction started at around 300°C with the rapid formation of LaOCl, and the release of CO2 into the gas phase. The complete transformation of LaOCl into LaCl3 was much more difficult to obtain, and required high reaction temperatures and large amounts of CCl4. In the case of CeO2, CCl4 destruction started at around 450°C, and was accompanied by the reduction of Ce(IV) to Ce(III) and the formation of CeOCl as an intermediate product. The complete transformation of CeO2 into CeCl3 was only observed at reaction temperatures near 600°C. These results are compared with those recently reported for alkaline earth metal oxides.

Abstract: In laboratory engine tests, a combination of platinum and cerium fuel additives with a platinum activated wall flow monolithic filter has been shown to be especially effective in the control of diesel particulate. Continuous regeneration of a filter can be achieved at temperatures of 600 K using 5 ppm of cerium and 0.5 ppm of platinum in EN590 fuel containing 500 ppm (wt) of sulfur.

Abstract: A fuel gas reformer assemblage for use in a fuel cell power plant is formed from a composite plate assembly which includes spaced-apart divider plates (22, 24, 26) with interposed columns of individual fuel gas (12) and burner gas (14) passages. The fuel gas passages (12) are provided with walls which are wash coated with a catalyzed alumina complex (28). The catalyst complex (28) includes a nickel catalyst and a cerium and/or lanthanum oxide component which stabilizes the alumina against recrystalization in the catalyst complex. The catalyst complex (28) also includes a calcium oxide component which inhibits carbon formation on the alumina surface. The cerium or lanthanum oxide and calcium oxide combine to provide a synergistic improvement in both alumina stabilization and also in inhibition of carbon deposits on the wash coated surfaces (28).

Abstract: Cerium oxide (IV) (CeO2) is extensively employed in heterogeneous catalysis, particularly as a promoter of noble metal action in three-way catalysts. For this reason there is a great scientific and economical interest in the development of any possible chemical or structural analysis technique that could provide information on these systems. EXAFS spectroscopy has revealed itself as a powerful technique for structural characterization of such catalysts. Unfortunately, good quality K-edge spectra of cerium are not yet easily obtainable because of the high photon energy required (>40 keV). On the other hand, at lower energies it is easy to collect very good spectra of the L3 edge (5.5 keV), but L3-edge spectra of cerium (IV) are characterized by the presence of two undesired additional phenomena that interfere with EXAFS analysis: final-state mixed-valence behaviour and intense multi-electron excitations. Here, a comparative analysis of the K, L3, L2 and L1 edges of Ce in CeO2 has been made and a procedure for obtaining structural parameters from L3-edge EXAFS, even in the presence of these features, has been developed. This procedure could allow further studies of catalytic compounds containing tetravalent cerium surrounded by oxygen ligands.

Abstract: We observed violet/blue light emitted from cerium silicates which may be useful for silicon-based optoelectronics The cerium silicate was produced during a rapid thermal annealing at high temperature (>1100 °C) from the interface between silicon substrate and cerium oxide film Detailed experiments including x-ray diffraction, high-resolution transmission electron microscope, and Auger depth profiling showed that the cerium silicate consists of Ce4667(SiO4)3O and Ce2Si2O7 phases The photoluminescence of the cerium silicate is very strong at room temperature Specifically, the 358 nm luminescence line is attributed to the Ce2Si2O7 phase