Remarkable stability of ionic gold supported on sulfated lanthanum oxide

Isolated cationic gold deposited on sulfated lanthanum oxide has been shown to exhibit remarkable stability opening a promising way of stabilising ionic gold for catalytic reactions.

Synthesis, Structure, and Spectroscopic Properties of the New Lanthanum(III) Fluoride Oxomolybdate(VI) La3FMo4O16

La3FMo4O16 crystallizes in the triclinic crystal system with space group P (1) over bar [a = 724.86(2) pm, b = 742.26(2) pm, c = 1469.59(3) pm, a = 101.683(2)degrees, beta 102.118(2)degrees, gamma = 100.279(2)degrees] with two formula units per unit cell. The three crystallographically independent La3+ cations show a coordination number of nine each, with one F- and eight O2- anions forming distorted monocapped square antiprisms. The fluoride anion is coordinated by all three lanthanum cations to form a nearly planar triangle. Besides three crystallographically independent tetrahedral [MoO4](2-) units, a fourth one with a higher coordination number (CN = 4 +1) can be found in the crystal structure, forming a dimeric entity with a formula of [Mo2O8](4-) consisting of two edge-connected square pyramids. Several spectroscopic measurements were performed on the title compound, such as infrared, Raman, and diffuse reflectance spectroscopy. Furthermore, La3FMo4O16 was investigated for its capacity to work as host material for doping with luminescent active cations, such as Ce3+ or Pr3+. Therefore, luminescence spectroscopic as well as EPR measurements were performed with doped samples of the title compound. Both the pure and the doped compounds can be synthesized by fusing La2O3, LaF3 and MoO3 (ratio 4:1:12; ca. 1 % CeF3 and PrF3 as dopant, respectively) in evacuated silica ampoules at 850 degrees C for 7 d.

Activation of Alkanes by Gold-Modified Lanthanum Oxide

Functionalization of alkanes is much sought after for the production of fine and bulk chemicals. In particular, the oxidative activation of alkanes and their conversion to ethene and propene has been studied extensively, owing to the use of these alkenes in polymerization reactions. The greater reactivity of the products in comparison with the reactants has proven a major issue in this reaction as this can result in overoxidation, producing CO and CO2 and, therefore, reducing the alkene yield. Herein, the first application of supported gold catalysts for the direct activation of C2+ aliphatic alkanes with oxygen to form alkenes is demonstrated. This catalyst is particularly notable as it is highly active, selective to propene and ethene, and stable on stream over a 48 h period. Maintaining cationic gold is thought to be critical for the stability and this catalyst design provides the possibility of applying gold-based catalysts over a much wider temperature range than has been reported.

A comparative study on the anisole methylation activity of lanthanum-promoted Sn02 catalyst and its sulfate-doped analogue

A comparative study on the anisole methylation with methanol over lanthanum-promoted Sn02 catalyst and its sulfate-doped analogue is presented. A maximum 2.6-xylenol selectivity of 82% was achieved at 400 degreeC under optimized conditions at an anisole conversion of 65% over lanthanum-promoted Sn02 catalyst. The sulfate modification resulted in the dealkylation of anisole to phenol followed by several unselective side reactions due to the creation of strong acid sites. The activity of lanthanum-modified tin oxide catalysts in the selective formation of 2.6-xylenol is ascribed to the presence of weak Lewis acid sites and comparatively stronger basic sites.

Basicity and electron donor properties of lanthanum oxide and its mixed oxides with alumina

The electron donating properties of La2O3 activated at 300, 500 and 800·C and its mixed oxides with alumina are reported from the studies on adsorption of electron acceptors of varying electron affinity on La203. The electron acceptors with their electron affinity values given in parenthesis are: 7,7,8,8-tetracyanoquinodimethane (2.84 eV), 2,3,5,6-tetrachloro-I,4-benzoquinone (2.40 eV) and p-dinitrobenzene(l.77eV). The basicity of the oxide has been determined by titration with n-butylamine and Ho.max values are reported. The limit of electron transfer from the oxide to the electron acceptor is between 2.40 and 1.77 eV. It is observed that La203 promotes the surface electron properties of alumina without changing its limit of electron transfer.

Catalytic activity of lanthanum oxide for the reduction of cyclohexanone

Lanthanum oxide, La2O3 has been found to be an effective catalyst for the liquid phase reduction of cyclohexanone. The catalytic activities of La2O3 activated at 300, 500 and 800·C and its mixed oxides with alumina for the reduction of cyclohexanone with 2-propanol have been determined and the data parallel that of the electron donating properties of the catalysts. The electron donating properties of the catalysts have been determined from the adsorption of electron acceptors of different electron affinities on the surface of these oxides.

Near fifty percent sodium substituted lanthanum manganites—A potential magnetic refrigerant for room temperature applications

Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J kg 1 K 1 was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62K at 280 K

Towards Realization of Magnetocaloric and Magnetoelectric Applications based on Bulk and Thin film forms of Sodium substituted Lanthanum Manganites

The present thesis work focuses on hole doped lanthanum manganites and their thin film forms. Hole doped lanthanum manganites with higher substitutions of sodium are seldom reported in literature. Such high sodium substituted lanthanum manganites are synthesized and a detailed investigation on their structural and magnetic properties is carried out. Magnetic nature of these materials near room temperature is investigated explicitly. Magneto caloric application potential of these materials are also investigated. After a thorough investigation of the bulk samples, thin films of the bulk counterparts are also investigated. A magnetoelectric composite with ferroelectric and ferromagnetic components is developed using pulsed laser deposition and the variation in the magnetic and electric properties are investigated. It is established that such a composite could be realized as a potential field effect device. The central theme of this thesis is also on manganites and is with the twin objectives of a material study leading to the demonstration of a device. This is taken up for investigation. Sincere efforts are made to synthesize phase pure compounds. Their structural evaluation, compositional verification and evaluation of ferroelectric and ferromagnetic properties are also taken up. Thus the focus of this investigation is related to the investigation of a magnetoelectric and magnetocaloric application potentials of doped lanthanum manganites with sodium substitution. Bulk samples of sodium substituted lanthanum manganites. Bulk samples of sodium substituted lanthanum manganites with Na substitution ranging from 50 percent to 90 percent were synthesized using a modified citrate gel method and were found to be orthorhombic in structure belonging to a pbnm spacegroup. The variation in lattice parameters and unit cell volume with sodium concentration were also dealt with. Magnetic measurements revealed that magnetization decreased with increase in sodium concentrations.

Uranyl(VI) and lanthanum(III) thio-diglycolamides complexes: synthesis and structural studies involving nitrate complexation

New tri-functional ligands of the type R2NCCCH2SCH2CCNR2 (where R = iso-propyl, n-butyl or iso-butyl) were prepared and characterized. The coordination chemistry of these ligands with uranyl and lanthanum(III) nitrates was studied by using the IR, (HNMR)-H-1 and elemental analysis methods. Structures for the compounds [UO2(NO3)(2)((Pr2NCOCH2SCH2CONPr2)-Pr-i-Pr-i)] [UO2(NO3)(2)((Bu2NCOCH2SCH2CONBu2)-Bu-i-Bu-i)(2)] [La(NO3)(3)((Pr2NCOCH2SCH2CONPr2)-Pr-i-Pr-i)(2)] and [La(NO3)(3)((Bu2NCOCH2SCH2CONBu2)-Bu-i-Bu-i)(2)] were determined by single crystal X-ray diffraction. These structures show that the ligand acts as a bidentate chelating ligand and bonds through both the carbamoyl groups to the uranyl and lanthanum(III) nitrate groups. Solvent extraction studies show that the ligand can extract the uranyl ion from the nitric acid medium but does not show any ability to extract the americium (III) ion. (C) 2009 Elsevier Ltd. All rights reserved.

Coordination and extraction studies of an unexplored bi-functional ligand, carbamoyl methyl pyrazole (CMPz) with uranium(VI), lanthanum(III) and cerium(III) nitrates

The bi-functional carbamoyl methyl pyrazole ligands, C5H7N2CH2CONBu2 (L-1), (C5H7N2CH2CONBu2)-Bu-i (L-2), C3H3N2CH2CONBu2 (L-3), (C3H3N2CH2CONBu2)-Bu-i (L-4) and C5H7N2CH2CON(C8H17)(2) (L-5) were synthesized and characterized by spectroscopic and elemental analysis methods. The selected coordination chemistry of L-1 to L-4 with [UO2(NO3)(2)center dot 6H(2)O], [La(NO3)(3)center dot 6H(2)O] and [Ce(NO3)(3)center dot 6H(2)O] has been evaluated. Structures for the compounds [UO2(NO3)(2) C5H7N2CH2CONBu2] (6) [UO2(NO3)(2) (C5H7N2CHCONBu2)-Bu-i] (7) and [Ce(NO3)(3){C(3)H(3)N(2)CH(2)CON(i)Bu2}(2)] (11) have been determined by single crystal X-ray diffraction methods. Preliminary extraction studies of the ligand L-5 with U(VI) and Pu(IV) in tracer level showed an appreciable extraction for U(VI) and Pu(TV) up to 10 M HNO3 but not for Am(III). Thermal studies of the compounds 6 and 7 in air revealed that the ligands can be destroyed completely on incineration. (c) 2007 Elsevier Ltd. All rights reserved.

Mononuclear single helices of lanthanum(III) and europium(III). Metal dependent diastereomeric excess

Using the 1: 2 condensate of benzildihydrazone and 2-acetylpyridine as a tetradentate N donor ligand L, LaL(NO3)(3) (1) and EuL(NO3)(3) (2), which are pale yellow in colour, are synthesized. While single crystals of 1 could not be obtained, 2 crystallises as a monodichloromethane solvate, 2 center dot CH2Cl2 in the space group Cc with a = 11.7099(5) angstrom, b = 16.4872(5) angstrom, c = 17.9224(6) angstrom and beta = 104.048(4)degrees. From the X-ray crystal structure, 2 is found to be a rare example of monohelical complex of Eu(III). Complex 1 is diamagnetic. The magnetic moment of 2 at room temperature is 3.32 BM. Comparing the FT-IR spectra of 1 and 2, it is concluded that 1 also is a mononuclear single helix. H-1 NMR reveals that both 1 and 2 are mixtures of two diastereomers. In the case of the La(III) complex (1), the diastereomeric excess is only 10% but in the Eu(III) complex 2 it is 80%. The occurrence of diastereomerism is explained by the chiralities of the helical motif and the type of pentakis chelates present in 1 and 2.

Preparation and structural characterization of rare-earth doped lead lanthanum zirconate titanate ceramics

A new preparation route towards rare-earth (RE) doped polycrystalline lead lanthanum zirconate titanate (PLZT) ceramics (RE = Y(3+), Nd(3+), Yb(3+)), based on the use of doped lanthanum oxide or zirconia, is reported. Structural characterization by X-ray powder diffraction reveals that secondary phase formation can be substantially diminished in comparison to conventional preparation methods. The distribution of the rare-earth dopants was investigated as a function of concentration by static (207)Pb spin echo NMR spectra, using Fourier Transformation of Carr-Purcell-Meiboom-Gill spin echo trains. For the Nd- and Yb-doped materials, the interaction of the (207)Pb nuclei with the unpaired electron spin density results in significant broadening and shifting of the NMR signal, whereas these effects are absent in the diamagnetic Y(3+) doped materials. Based on different concentration dependences of the NMR lineshape parameters, we conclude that the structural role of the Nd(3+) dopants differs significantly from that of Yb(3+). While the Nd(3+) ions appear to be statistically distributed in the PLZT lattice, incorporation of Yb(3+) into PLZT appears to be limited by the appearance of doped cubic zirconia as a secondary phase. (C) 2009 Elsevier Masson SAS. All rights reserved.

Solid state NMR as a new approach for the structural characterization of rare-earth doped lead lanthanum zirconate titanate laser ceramics

To facilitate the design of laser host materials with optimized emission properties, detailed structural information at the atomic level is essential, regarding the local bonding environment of the active ions (distribution over distinct lattice sites) and their extent of local clustering as well as their population distribution over separate micro- or nanophases. The present study explores the potential of solid state NMR spectroscopy to provide such understanding for rare-earth doped lead lanthanum zirconate titanate (PLZT) ceramics. As the NMR signals of the paramagnetic dopant species cannot be observed directly, two complementary approaches are utilized: (1) direct observation of diamagnetic mimics using Sc-45 NMR and (2) study of the paramagnetic interaction of the constituent host lattice nuclei with the rare-earth dopant, using Pb-207 NMR lineshape analysis. Sc-45 MAS NMR spectra of scandium-doped PLZT samples unambiguously reveal scandium to be six-coordinated, suggesting that this rare-earth ion substitutes in the B site. Static Pb-207 spin echo NMR spectra of a series of Tm-doped PLZT samples reveal a clear influence of paramagnetic rare-earth dopant concentration on the NMR lineshape. In the latter case high-fidelity spectra can be obtained by spin echo mapping under systematic incrementation of the excitation frequency, benefiting from the signal-to-noise enhancement afforded by spin echo train Fourier transforms. Consistent with XRD data, the Pb-207 NMR lineshape analysis suggests that statistical incorporation into the PLZT lattice occurs at dopant levels of up to 1 wt.% Tm3+, while at higher levels the solubility limit is reached. (C) 2008 Elsevier Masson SAS. All rights reserved.