Showing papers on "Lanthanum published in 2007"
TL;DR: In this article, the authors investigated the protective behavior of bis-triethoxysilylpropyl tetrasulfide silane pre-treatments on the AZ31 Mg alloy.
207 citations
TL;DR: In this paper, two pre-treatments were studied for AZ31 Mg alloy substrates, consisting of immersion in cerium nitrate and lanthanum nitrate solutions for various immersion times.
189 citations
TL;DR: In this paper, the performance of ethanol reforming over nickel catalysts supported on lanthanum loaded Al 2 O 3 substrates was studied and the results revealed the enhancement in the reforming stability of the Ni catalysts with the increase in the lanthanums loading on Al 2 o 3 substrate.
171 citations
TL;DR: The results suggest that methane activation proceeds through oxidation-reduction reactions on the surface of catalysts with an irreducible metal-lanthanum, which is significantly different from known mechanisms for oxidative chlorination.
Abstract: The mechanism of selective production of methyl chloride by a reaction of methane, hydrogen chloride, and oxygen over lanthanum-based catalysts was studied. The results suggest that methane activation proceeds through oxidation-reduction reactions on the surface of catalysts with an irreducible metal-lanthanum, which is significantly different from known mechanisms for oxidative chlorination. Activity and spectroscopic measurements show that lanthanum oxychloride (LaOCl), lanthanum trichloride (LaCl3), and lanthanum phases with an intermediate extent of chlorination are all active for this reaction. The catalyst is stable with no noticeable deactivation after three weeks of testing. Kinetic measurements suggest that methane activation proceeds on the surface of the catalyst. Flow and pulse experiments indicate that the presence of hydrogen chloride is not required for activity, and its role appears to be limited to maintaining the extent of catalyst chlorination. In contrast, the presence of gas-phase oxygen is essential for catalytic activity. Density-functional theory calculations suggest that oxygen can activate surface chlorine species by adsorbing dissociatively and forming OCl surface species, which can serve as an active site for methane activation. The proposed mechanism, thus, involves changing of the formal oxidation state of surface chlorine from -1 to +1 without any changes in the oxidation state of the underlying metal.
166 citations
TL;DR: In this paper, the effect of LaCl3 and CeCl3 inhibitor additions in 3.5% NaCl solution on the corrosion behavior of aluminum alloy AA2014 has been investigated.
144 citations
TL;DR: In this paper, two nanostructured bulk LaCoO3 powders were prepared by co-precipitation and with the citrate gel method and compared with the two nanocomposites obtained depositing, by wet impregnation, cobalt oxide on the La2O3 surface.
Abstract: Two nanostructured bulk LaCoO3 powders were prepared by co-precipitation and with the citrate gel method and compared with the two nanocomposites obtained depositing, by wet impregnation, cobalt oxide on the La2O3 surface. All the prepared samples were characterized by means of X-ray photoelectron (XP) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. XRD results suggest that only the citrate gel method allows to obtain a single phase lanthanum cobaltite powder having a rhombohedral perovskite structure. Moreover, SEM images confirm the wide scale homogeneity. In contrast, a lanthanum hydroxide phase (hexagonal) is also evident in the sample obtained by co-precipitation method. In the nanocomposite richer in cobalt, besides the rhombohedral perovskite, the hexagonal lanthanum oxide and hydroxide phases are also detectable. Perovskite phase does not form when the amount of deposited cobalt oxide is too low. Both in the nanostructured sample prepared by citrate gel method and nanocomposite with [Co/La]nominal = 1.0 XPS, DRIFT and TGA outcomes suggest a lower presence of hydroxyl groups and carbonates species. The reactivity of the powders with respect to carbon monoxide was studied (at atmospheric pressure, between RT and 573 K) by means of the diffuse reflectance infrared Fourier transform spectroscopy. A significant signal around 2058 cm−1 testifies about the interaction of CO with the Lewis acidic sites distributed on the surface of all the samples. The two nanostructured bulk LaCoO3 show a high reactivity toward CO oxidation since 423 K. A similar oxidation capability is observed also for the nanocomposite richer in cobalt. In contrast, a rather low reactivity is displayed from the nanocomposite with lower Co/La nominal atomic ratio and La2O3.
134 citations
TL;DR: In this paper, a review of different methods of recovery of lanthanides in phosphate rock is presented, showing that more than 80% can be recovered without interference with fertiliser production when the rock is leached with HNO3 or HC1.
Abstract: Phosphate rock contains up to 1% lanthanide (rare earths) oxides present in isomorphous substitution for Ca2+. Lanthanum, cerium and neodymium form about 80% of the total. When the rock is leached with H2SO4 the lanthanides are mostly (about 70%) lost in the gypsum residue. When the rock is leached with HNO3 or HC1, more than 80% can be recovered without interference with fertiliser production. At an annual production of 130 million tons, phosphate rock represents an important source of lanthanides. The different methods of recovery are reviewed.
120 citations
TL;DR: Direct catalytic asymmetric Mannich-type reaction of a trichloromethyl ketone as a propionate equivalent donor is described, and the Mannich adduct was converted not only into ester but also into useful building blocks.
Abstract: Direct catalytic asymmetric Mannich-type reaction of a trichloromethyl ketone as a propionate equivalent donor is described. A new lanthanum aryloxide−iPr-pybox + lithium aryloxide combined catalys...
100 citations
TL;DR: In this article, the perovskite type lanthanum chromite LaCrO3 has been synthesized by a sol-gel method and its bulk structural and surface characteristics have been examined by X-ray diffraction (XRD), SEM, SBET measurements, Fourier Transform Infrared (FTIR) and Xray photoelectron spectroscopy (XPS) as a function of the calcination treatment performed between 200 and 1000°C over the precursor powder.
Abstract: The perovskite type lanthanum chromite LaCrO3 has been synthesized by a sol–gel method. Its bulk structural and surface characteristics have been examined by X-ray diffraction (XRD), SEM, SBET measurements, Fourier Transform Infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) as a function of the calcination treatment performed between 200 and 1000 °C over the precursor powder and in correlation with information achieved from TG-DTA thermal analysis. The characterization results are employed to rationalize the catalytic behaviour of the system towards propene complete oxidation. It is shown that the catalytic activity becomes optimized when a single perovskite LaCrO3 phase is achieved upon calcination at T > ca. 700 °C. In contrast, coexistence of perovskite LaCrO3 and monazite LaCrO4 at lower calcination temperatures appears detrimental to the combustion activity of the system.
99 citations
TL;DR: In this paper, the authors investigated the selective synthesis of phytosterol esters from natural sterols and methyl esters using basic solids that are reusable, active, and more selective than the currently used homogeneous catalysts (e.g., alkali hydroxides, carbonates).
97 citations
TL;DR: In this article, a series of lanthanum doped mesoporous SiO 2 (La-meso-SiO 2 ) were synthesized and characterized by X-ray diffraction, N 2 adsorption-desorption, and Fourier transform infrared spectroscopy.
TL;DR: In this paper, the performance of LaCoO3-based catalysts in ethanol combustion and their selectivity to acetaldehyde formation can be explained on the basis of the presence of both α-oxygen species and sites with basic character on the material surface.
Abstract: Ce- or Sr-doped LaCoO3 bulk perovskites were prepared by citric acid method as well as 10 wt.% of LaCoO3 was deposited on alumina carrier stabilized with lanthanum. Properties of prepared materials were characterized by determination of surface area, acid-basic properties and XRD, XPS, TPDO2, H2-TPR measurements as well as catalytic activity and selectivity for ethanol combustion was tested. It was found that substitution of La in LaCoO3 with either Sr or Ce has only small effect on its activity in ethanol combustion. Strontium inserted into LaCoO3 structure increases basic character of the perovskite surface as well as selectivity to acetaldehyde (ACA). Substitution of La with cerium has no effect on the concentration of basic sites and does not affect the selectivity to ACA. Activity of LaCoO3-based catalysts in ethanol combustion and their selectivity to ACA formation can be explained on the basis of the presence of both α-oxygen species and sites with basic character on the material surface. Acid-basic properties of supported LaCoO3 are dominated by acidic character of the carrier. Results of XPS and H2-TPR measurements of LaCoO3 supported on La–Al2O3 suggest that perovskite remains in strong interaction with carrier and probably is partially decomposed. Deposition of perovskite on stabilized carrier significantly increases the rate of ethanol combustion.
TL;DR: In this article, the oxide ion conductivity of apatite-type lanthanum silicates has been enhanced by cation doping into both La and Si sites, by creating excess oxide ions and increasing the conductivity.
Abstract: The oxide ion conductivity of apatite-type lanthanum silicates has been enhanced by cation doping into both La and Si sites. The Sr and Nd fill vacancies on the La site by creating excess oxide ions and increasing the conductivity. Al and Mg, which substitute for Si at a fixed oxygen content, result in an enhancement of conductivity, accompanied by lattice enlargement. The Mg-doped lanthanum silicate, La9.533(Si5.7Mg0.3)O26, has been shown to have the highest conductivity of 4.4 × 10−2 S/cm at 800°C. The conduction channel consists of La triangles and O triangles, and the channel sizes have been calculated from the Rietveld structure analysis of the powder X-ray diffraction patterns. Expansions of the O triangles have been observed when introducing excess oxide ions by filling vacancies on the La site or by the substitution of Si using dopants.
TL;DR: The total reflux method as applied to the separation of rare earth elements is outlined with reference to extractants Versatic 911, tributyl phosphate and di-2-ethylhexyl phosphoric acid.
Abstract: The total reflux method as applied to the separation of rare earth elements is outlined with reference to extractants Versatic 911, tributyl phosphate and di-2-ethylhexyl phosphoric acid Industrial solvent extraction processes are described for the production of pure compounds of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium and yttrium
TL;DR: In this article, the corrosion inhibition of pure Al due to addition of different concentrations of LaCl 3 and CeCl 3 in 3.5% NaCl solution has been investigated.
TL;DR: In this article, the results of X-ray diffraction and Raman spectroscopy showed that all powders crystallite calcined at 800 degrees C were single phase with cubic fluorite structure, the average crystallite sizes calculated by the Scherrer formula were between 27 and 34 nm.
TL;DR: In this paper, the synthesis of rod-shaped nanocrystalline lanthanum phosphate with an average length of 40 nm has been realized through a room-temperature aqueous sol-gel process.
Abstract: Synthesis of rod-shaped nanocrystalline lanthanum phosphate with an average length of 40 nm even after calcination at 400 °C has been realized through a room-temperature aqueous sol-gel process. The sol is characterized by particle-size, zeta-potential, and viscosity measurements. Gelation of the sol is induced by ammonia. The lanthanum phosphate phase-formation process is followed by thermal, Fourier-transform IR, and X-ray diffraction analysis. Transmission electron microscopy shows that the sol and gel particles have a rod-shaped morphology and comparable particle sizes. Using the Scherrer equation a crystallite size of 11 nm is obtained for the gel powder calcined at 400°C and Brunauer-Emmett-Teller (BET) nitrogen-adsorption analysis showed a high specific surface area of 100 m 2 g -1 . Ammonia temperature-programmed desorption measurements show that the density of Lewis acid sites is four times higher than ever reported in the case of lanthanum phosphates. The catalytic activity of the above sample is demonstrated by using it as a Lewis-acid catalyst in an acetal-formation reaction with a very good yield of 85 %. The sol is used to develop nanocoatings on a glass surface and the morphology of the coatings is investigated using atomic force microscopy and scanning electron microscopy. The microstructure of the coating confirmed the rod-shaped nature of the sol particles. The coating was uniform with a thickness of about 55 nm.
TL;DR: In this article, mixed oxides of nickel, magnesium and aluminum were prepared by precursors hydrotalcite type and were substituted by lanthanum or cerium using the method of anion exchange.
Abstract: Mixed oxides of nickel, magnesium and aluminum were prepared by precursors hydrotalcite type and were substituted by lanthanum or cerium using the method of anion exchange. The catalysts were characterized by X-Ray Photoelectronic Spectroscopy (XPS); Energy Dispersive X-Ray Spectroscopy (EDS); Surface Area Method BET; X-Ray Diffraction (XRD); Temperature Programmed Reduction (TPR) and Catalytic Tests. Analysis of the mixed oxides suggests that the hydrotalcite type precursor after thermal treatment lead a good dispersion of nickel forming the periclase (Ni, Mg)O replaced by cations of Al 3+ and spinel structure (Ni,Mg)Al 2 O 4 . The catalysts were tested in the partial oxidation of methane and the results showed that the catalysts promoted with lanthanum and cerium led to a reduction in the velocity of the carbon formation.
TL;DR: In this paper, a series of lanthanum benzoate complexes have been prepared and structurally characterised as DMF or DMSO solvates, and the structures of these complexes vary considerably as a function of the steric bulk of the ligands and the degree of solvation.
Abstract: A series of lanthanum benzoate complexes have been prepared and structurally characterised as DMF or DMSO solvates. The structures of these complexes vary considerably as a function of the steric bulk of the ligands and the degree of solvation. With one exception, all of the complexes form coordination polymers. These experimental results are compared to reported data from the Cambridge Structural Database (CSD) in order to study the role of sterically bulky substituents in the structures of lanthanum benzoate complexes. Binding modes vary from the η1 coordination of a carboxylic acid co-ligand to carboxylate ligands adopting a bridging μ-η2 : η1 geometry. The nature of the bridging environment between adjacent lanthanum ions varies significantly in the structures and often several different environments exist within the same structure. Solvent effects are also observed, particularly in cases where the solvent is able to partake in intra- or intermolecular hydrogen bonding.
TL;DR: In this paper, the effect of lanthanum ion substitution for iron on the structural and magnetic properties of Ni-Cu-Zn ferrite was reported, and the Rietveld structure refinement was carried out; La solubility in spinel, residual stress in sintered core, quantity of secondary LaFeO 3 phase formed and change in lattice parameters, etc.
Patent•
14 Feb 2007TL;DR: In this article, the catalysts comprising copper chromite, palladium and lanthanum have been shown to have hydrogenation activity and are useful for the preparation of methanol from carbon monoxide and hydrogen and for the hydrogenation of carbonyl compounds such as aldehydes, ketones, and esters.
Abstract: Disclosed are catalysts comprising copper chromite, palladium and lanthanum having hydrogenation activity. The combination of copper chromite with palladium and lanthanum enhances catalyst activity more than the presence of either palladium alone or palladium in combination with alkali or alkaline earth metals. The catalysts are useful for the preparation of methanol from carbon monoxide and hydrogen and for the hydrogenation of carbonyl compounds such as, for example, aldehydes, ketones, and esters, to their corresponding alcohols. The catalysts may be used for the preparation of cyclohexanedimethanols from dialkyl cyclohexanedicarboxylates or of ethylene glycol from alkyl glycolates.
TL;DR: Lanthanum-doped MCM-48 molecular sieves with different La contents were synthesized hydrothermally and characterized by X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), UV-visible spectroscopy, and Fourier transform infrared (FT-IR) spectroscopic.
Abstract: Lanthanum-doped MCM-48 molecular sieves with different La contents were synthesized hydrothermally and characterized by X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), UV−visible spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. The results show that the majority of La cations have been incorporated into the framework of MCM-48 molecular sieves. When the molar ratio of La/Si is >0.039 in the sample, some of lanthanum species exist in the extraframework. Compared with pure silicate MCM-48, lanthanum-doped MCM-48 samples show the medium strong acidity that is due to the incorporation of La in the framework of silica. In the oxidation of styrene with H2O2 as the oxidant over the lanthanum-doped MCM-48 catalysts, benzaldehyde is the main product with a small amount of styrene oxide. The La content in the catalysts, reaction temperature, reaction time, and solvent affect greatly the catalytic oxidation of styrene. The conversion of styrene and the selectivit...
Patent•
03 Jan 2007TL;DR: In this paper, a two-layer system is proposed to prevent CMAS infiltration at the interface of the outer layer of TBC and the CMAS, where the inner layer consists of partially stabilized zirconium oxide.
Abstract: A coating applied as a two layer system. The outer layer (22) is an oxide of a group IV metal selected from the group consisting of zirconium oxide, hafnium oxide and combinations thereof, which are doped with an effective amount of a lanthanum series oxide. These metal oxides doped with a lanthanum series addition comprises a high weight percentage of the outer coating (22). When the zirconium oxide is doped with an effective amount of a lanthanum series oxide, a dense reaction layer is formed at the interface of the outer layer of TBC and the CMAS. This dense reaction layer prevents CMAS infiltration below it. The second layer, or inner layer (20) underlying the outer layer (22), comprises a layer of partially stabilized zirconium oxide.
TL;DR: In this paper, the authors applied H MAS NMR spectroscopy to quantify the concentration of hydroxyl groups on lanthanum- exchanged zeolites X and Y as a function of the dehydration temperature.
TL;DR: In this article, the preparation of lanthanum hydroxide and manganese oxide nanoparticles is presented, based on a nonaqueous sol-gel process involving the reaction of La(OiPr)3 and KMnO4 with organic solvents such as benzyl alcohol, 2-butanone and a 1:1 vol. mixture thereof.
TL;DR: In this paper, the high-pressure structural behavior of lanthanum monochalcogenides is investigated by theory and experiment, which comprises density-functional calculations of LaS, LaSe, and LaTe with the general gradient approximation for exchange and correlation effects, as implemented within the fullpotential linear muffin-tin orbital method.
Abstract: The high-pressure structural behavior of lanthanum monochalcogenides is investigated by theory and experiment. Theory comprises density-functional calculations of LaS, LaSe, and LaTe with the general gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. The experimental studies consist of high-pressure angle dispersive x-ray-diffraction investigations of LaS and LaSe up to a maximum pressure of 41 GPa. A structural phase transition from the NaCl-type to CsCl-type crystal structure is found to occur in all cases. The experimental transition pressures are 27-28 and 19 GPa for LaS and LaSe, respectively, while the calculated transition pressures are 29, 21, and 10 GPa for LaS, LaSe, and LaTe, respectively. The calculated ground-state properties such as equilibrium lattice constant, bulk modulus and its pressure derivative, and Debye temperatures are in good agreement with experimental results. Elastic constants are predicted from the calculations.
TL;DR: In this article, La-In-based oxysulfide is demonstrated to act as a photocatalyst for the reduction of H + to H 2 and the oxidation of H 2 O to O 2 in the presence of sacrificial reagents under visible light.
Abstract: La-In-based oxysulfide is demonstrated to act as a photocatalyst for the reduction of H + to H 2 and the oxidation of H 2 O to O 2 in the presence of sacrificial reagents under visible light (420 ≤ λ≤ 480 nm). Loading with IrO 2 is effective for promoting O 2 evolution, while Pt is effective as a cocatalyst for H 2 evolution.
TL;DR: In this paper, the effects of lanthanum incorporation into HfO2 dielectrics were studied using first-principles total energy calculations, and it was shown that the formation energy of a neutral oxygen vacancy (VO0) in the vicinity of substitutional La atoms at Hf sites is 0.7eV larger than that in pure Hf O2, indicating that the concentration of VO0's is drastically reduced by La incorporation.
Abstract: The effects of lanthanum incorporation into HfO2 dielectrics were studied using first-principles total energy calculations. The author’s computational result clearly showed that the formation energy of a neutral oxygen vacancy (VO0) in the vicinity of substitutional La atoms at Hf sites is 0.7eV larger than that in pure HfO2, indicating that the concentration of VO0’s is drastically reduced by La incorporation. This effect is understood to be caused by the decrease in the local dielectric constant κL around La atoms due to the strong ionic character of the La–O bond compared to the Hf–O bond.
TL;DR: In this paper, the influence of barium doping on the microstructural and electrochemical properties of the apatite phase La 10− x Ba x (SiO 4 ) 6 O 3− x /2 with x ǫ = 0.25-2.
Abstract: The main task in SOFC research is the reduction of the working temperature down to the range 700–800 °C. Apatite ceramics are interesting alternative SOFC electrolytes because of their open structure including tunnels for the diffusion of oxide ions and their good chemical stability. This study reports the influence of barium doping on the microstructural and electrochemical properties of the apatite phase La 10− x Ba x (SiO 4 ) 6 O 3− x /2 with x = 0.25–2. This doping range allows theoretical stoichiometric and overcharged apatite (more than two oxide ions in the tunnel). X-ray diffraction results on fired pellets show total insertion of the barium in the apatite lattice with a linear increase of the lattice parameters following the barium rate. Ionic conductivities are measured under air by impedance spectroscopy between 400 and 900 °C. The results are compared with apatite phases doped with calcium and strontium on the La site.
TL;DR: In this article, a two-dimensional salicylaldimine lanthanum coordination polymer is proved by the X-ray diffraction analysis of a new Lanthanum(III) nitrate complex containing the N,N′-bis(salicylidene)-1,4-butanediamine ligand L.