Showing papers on "Lanthanum published in 2018"

Synthesis and Stability of Lanthanum Superhydrides.

Abstract: Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen-rich simple compounds having new clathrate-like structures and remarkable electronic properties including room-temperature superconductivity. X-ray diffraction and optical studies demonstrate that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty-two hydrogen atoms surrounding each La atom. Upon decompression, the fcc-based structure undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H-H distances of about 1.1 A, which are close to predictions for solid atomic metallic hydrogen at these pressures. With stability below 200 GPa, the superhydride is thus the closest analogue to solid atomic metallic hydrogen yet to be synthesized and characterized.

Lanthanum-Doped Hafnium Oxide: A Robust Ferroelectric Material.

Abstract: Recently simulation groups have reported the lanthanide series elements as the dopants that have the strongest effect on the stabilization of the ferroelectric non-centrosymmetric orthorhombic phas...

Examination of the influence of La promotion on Ni state in hydrotalcite-derived catalysts under CO2 methanation reaction conditions: Operando X-ray absorption and emission spectroscopy investigation

Abstract: Hydrotalcite-derived Ni-containing and Ni-La promoted catalysts showed very high activity in CO2 methanation, which is an efficient way of carbon dioxide conversion into methane – a valuable product. The catalysts were obtained by co-precipitation method followed by thermal decomposition and characterized by elemental analysis, low temperature nitrogen sorption, XRD, H2-TPR, CO2-TPD and TEM. The obtained results confirmed the formation of periclase-like structure materials, with nickel present as NiO nanoparticles and suggested successful incorporation of lanthanum into the catalytic system. The addition of lanthanum changed the interaction between nickel and periclase matrix (H2-TPR) and changed the distribution of basic sites, especially medium strength ones (CO2-TPD). Moreover, the catalysts were studied by complementary HERFD-XANES and XES spectroscopy under model operando conditions. The results uncovered that the presence of lanthanum strongly influenced the chemical nature and oxidation state of nickel species and its crucial role in catalyst activity enhancement in CO2 methanation reaction.

Mechanism studies on methyl orange dye degradation by perovskite-type LaNiO3-δ under dark ambient conditions

Abstract: Perovskite materials have attracted much attention in heterogeneous catalysis. Here, we report a perovskite type material LaNiO3-δ (LNO) for degradation of methyl orange (MO) azo dye in aqueous solutions under dark ambient conditions (room temperature, atmospheric pressure) without additional lights or chemical stimulants. The high degradation percentage of 5 ppm MO with 1.5 g/L LNO was 94.3% after 4 h with a stirring speed of 500 rpm. Reactions under nitrogen, oxygen and carbon dioxide conditions were performed with efficiencies of 19.6%, 7.1%, and 96.8% respectively after 6 h to understand the mechanism. MO was shown to degrade under dark ambient condition via main intermediates, sulfanilic acid anion and N,N-dimethyl-p-phenylenediamine (DPD), by electrospray ionization mass spectrometry (ESI/MS) and high performance liquid chromatography (HPLC). Degradation of MO under such a mild condition is due to two synergic effects proposed by means of XRD, FTIR, TGA, SEM, and XPS. Nickel is oxidized during MO degradation; lanthanum carbonate (La-analog calkinsite) is formed on the LNO surface due to the aqueous solution environment and speeds up azo bond cleavage. This work unravels the mechanism behind MO degradation by LNO under dark ambient conditions for the first time. It is a fundamental information on perovskite for dye degradation, especially for lanthanum series of perovskite. Excellent perovskite materials should be tailorable for water remediation applications considering the large variety of perovskites in terms of constituents and composition.

The investigation of the role of basic lanthanum (La) species on the improvement of catalytic activity and stability of HZSM-5 material for eliminating methanethiol-(CH3SH)

Abstract: Lanthanum (La)-doped HZSM-5 and HZSM-5 catalysts were prepared to investigate the natural roles of La addition on the catalytic performance of HZSM-5 for decomposing methanethiol (CH3SH). Compared to HZSM-5, the incorporation of La species into HZSM-5 catalyst not only decreased the intrinsic activation energy (from 51.4 kJ/mol to 40.6 kJ/mol) but also largely improved the stability. Based on the characterizations of X-ray diffraction pattern (XRD), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of carbon dioxide (CO2-TPD), temperature-programmed desorption of ammonia (NH3-TPD), and temperature programmed desorption of CH3SH (CH3SH-TPD), the promotional role of La species on the catalytic activity was demonstrated to be the contribution of the surface active oxygen species within lanthanum oxy-carbonates composites, which not only might act as new active sites for converting CH3SH into CO2 but also could decrease the activation temperature for the dehydrogenation of CH3SH into intermediate, dimethyl sulfide (CH3SCH3). The enhanced stability of La doped HZSM-5 was attributed to the synergistic effect of the decrease in the strong acid sites as well as the formed CO2 and surface lanthanum oxy-carbonates layer. The rapid deactivation of HZSM-5 was due to the formation of deposited coke irrespective of deposited sulfur species. The nature, amount and type of deposited coke were investigated in detail via the characterization of FTIR, Raman spectroscopy, temperature programmed oxidation of oxygen (O2-TPO), thermogravmetric analysis (TGA). A facile and rapid regeneration method was used to regenerate spent La doped HZSM-5 and no significant deactivation was observed even after three cycles of deactivation-regeneration.

Tunable assembly of porous three-dimensional graphene oxide-corn zein composites with strong mechanical properties for adsorption of rare earth elements

Abstract: Three-dimensional (3D) graphene oxide (GO)-based porous composites with strong compressive mechanical properties were prepared by self-assembly of corn zein (CZ) and GO through a facile hydrothermal process, which were used for the adsorption of rare earth elements (REEs) from aqueous solutions. The adsorption equilibrium for REEs by GO CZ composites could be achieved within 200 min. And the maximum adsorption capacities of GO CZ9:1 for yttrium (Y), lanthanum (La), erbium (Er), ytterbium (Yb) and neodymium (Nd) were 14.2, 17.29, 11.72, 10.08 and 9.68 mg g−1, respectively. The relatively high desorption rate (85–95%) of 3D GO CZ9:1 composite represents a higher reproducibility. Moreover, the 3D GO CZ composites obtained with a mass ratio of 3:1, 5:1 and 9:1 for GO and CZ could be compressed to 60% of their original volumes and gradually restored to their original morphologies under the corresponding stresses of 18, 16 and 11 KPa, respectively. The adsorption mechanism was also proposed.

Niobium Doped Lanthanum Strontium Ferrite as A Redox-Stable and Sulfur-Tolerant Anode for Solid Oxide Fuel Cells.

Abstract: A novel Nb-doped lanthanum strontium ferrite perovskite oxide La0.8Sr0.2Fe0.9Nb0.1O3-δ (LSFNb) is evaluated as anode material of solid oxide fuel cell (SOFC). The effects of Nb partial substitution on the crystal structure, electrical conductivity and valence of Fe ions are studied. A good structural stability of LSFNb in severe reducing atmosphere at 800 °C is found, suggesting that high valent Nb can effectively promote the stability of lattice structure. The ratio of Fe2+ increases after Nb doping as confirmed by the results of XPS. The maximum power density of a thick Sc-stabilized zirconia (ScSZ) electrolyte supported single cell reached 241.6 mW·cm-2 at 800 °C using H2 as fuel. The cell exhibited excellent stability for continuously 100 h operation without detectable degeneration. SEM images clearly revealed the exsolutions on LSFNb surface after operation. Meanwhile, LSFNb particles agglomerated obviously during long-term stability test. Impedance spectra suggested that both LSFNb anode and (La0.75Sr0.25)0.95MnO3-δ (LSM)/ScSZ cathode exhibited an activation process during long-term test, through which the ability of charge transfer increases obviously. Meanwhile, low-frequency resistance (RL) mainly attributed by anode (80%) significantly increased, probably due to the agglomeration of LSFNb particles. The LSFNb anode exhibits excellent anti-sulfuring poisoning ability and redox stability. These results demonstrate that LSFNb is a promising anode material for SOFC.

On the role of Ce in CO2 adsorption and activation over lanthanum species

Abstract: La2O3 exhibits good performance for various catalytic applications, such as oxidative coupling of methane (OCM) and dry reforming of methane (DRM), during which coke formation may lead to the deactivation of catalysts. Typically, the reaction between CO2 adsorbed on La2O3 and coke is the rate-determining step of the coke elimination process. This paper describes the influence of Ce addition on the CO2 adsorption and activation over La2O3. Combined with in situ and ex situ characterization and density functional theory (DFT) calculation, we show that Ce addition promotes the formation of bidentate carbonate on La2O3via tuning CO2 adsorption energy. In addition, Ce addition adjusts the ratio of bidentate/monodentate carbonate, and affects the ratio of hexagonal/monoclinic La2O2CO3 on the binary oxides. DRM is used as a probe reaction to examine the coke elimination performance of Ce-La binary oxide. It is found that when the Ce/La ratio reaches the optimal value (0.15), Ce-La binary oxide has the highest CO2 adsorption energy and predominantly promotes the formation of bidentate carbonate, and hence possesses the highest basicity above 700 °C and finally exhibits the best coke elimination performance.

The accumulation of La, Ce and Y by Lemna minor and Lemna gibba in the Keban gallery water, Elazig Turkey

Abstract: This study investigated the phytoremediation ability of Lemna minor and Lemna gibba to accumulate lanthanum, cerium and yttrium from gallery water polluted by metals. L. minor and L. gibba were settled in the mining water and adapted to separate reactors. During the experiment, the water and plant samples were daily taken and the temperature, electric conductivity and pH of the water were daily measured in situ. These plants were firstly washed, dried in and then ashed at 300°C for 24 h in an oven. Both water and ashed plant samples were measured by ICP-MS to detect the concentrations of lanthanum (La), cerium (Ce) and yttrium (Y). Although these elements are at low concentrations in gallery water, they were accumulated at the highest levels in L. gibba and in L. minor. This study showed that both plants have high ability to remove lanthanum, cerium and yttrium in gallery water polluted by different elements.

Roles of Lanthanum and Cerium in Grain Refinement of Steels during Solidification

Abstract: Refinement of as-cast structures is one of the most effective approaches to improve mechanical properties, formability, and surface quality of steel castings and ingots. In the past few decades, addition of rare earths (REs), lanthanum and cerium in particular, has been considered as a practical and effective method to refine the as-cast steels. However, previous reports contained inconsistent, sometime even contradictory, results. This review summaries the major published results on investigation of the roles of lanthanum or/and cerium in various steels, provides reviews on the similarity and difference of previous studies, and clarifies the inconsistent results. The proposed mechanisms of grain refinement by the addition of lanthanum or/and cerium are also reviewed. It is concluded that the grain refinement of steels by RE additions is attributed to either heterogeneous nucleation on the in-situ formed RE inclusions, a solute effect, or the combined effect of both. The models/theories for evaluation of heterogeneous nucleation potency and for solute effect on grain refinement of cast metals are also briefly summarized.

Kinetics, mechanism, and thermodynamics of lanthanum adsorption on pectin extracted from durian rind

Abstract: The rare-earth elements in aqueous waste streams have received great attention due to their potential to pollute the environment. Lanthanum is one of the most used rare-earth elements in industries and disposed as waste. Several efforts have been devoted to remove lanthanum from waste water systems. This study was focused on the adsorption of lanthanum from aqueous solutions by using pectin extracted from durian rind, which is home and industrial waste of durian fruit. Adsorption experiments were carried out in batch method, and the effects of contact time, initial concentration of lanthanum ion, pH of medium, pectin dosage, and temperature on the adsorption efficiency were investigated. The kinetics, mechanism, and thermodynamics of lanthanum adsorption on the pectin were also evaluated. The results demonstrated that the pectin as a cost-effective biosorbent could remove lanthanum with efficiency as high as 41.2 mg/g (at the optimum conditions: pH 4.0, 25 °C, 90 min). The adsorption process of lanthanum on the pectin is well described by either Freundlich or Temkin isotherm model, indicating that adsorption occurs mainly on multilayers and heterogeneous surfaces of pectin. Thermodynamic quantities suggested that the adsorption of lanthanum on the pectin was exothermic and spontaneous, and the reaction was feasible. We also showed that the spent adsorbent can be regenerated up to a limited number of times, upon strong base treatment.

The effect of sintering process on lithium ionic conductivity of Li6.4Al0.2La3Zr2O12 garnet produced by solid-state synthesis

Abstract: Recently, solid-state electrolyte lithium lanthanum zirconium oxide garnet (Li7La3Zr2O12, LLZO) has attracted great attention due to its high room temperature conductivity of lithium ions and stability against lithium metal electrodes. The Al-doped cubic garnet Li6.4Al0.2La3Zr2O12 was synthesized by a conventional solid-state method at different sintering temperatures. The influence of the sintering process on the structure and ionic conductivity was investigated by X-ray diffraction, electrochemical impedance spectroscopy, and scanning electron microscopy. The results showed that Li vaporization and relative density were affected by the sintering process. The synergistic effects of Li concentration and relative density determined the Li+ ionic conductivity. Compared with the relative density, the Li concentration plays a more important role in determining the ionic conductivity via the solid-state method.

A Mechanistic Approach for the Synthesis of Carboxylate-Rich Carbonaceous Biomass-Doped Lanthanum-Oxalate Nanocomplex for Arsenate Adsorption

Abstract: Considering the protocol of “zero-alkaline waste disposal” for green and arsenic-free environment, lanthanum (La3+)-based MOF-like complex materials were designed, and the complex materials have been employed as adsorbent for AsO43– adsorption from water. The sucrose-derived porous carbon (SPC)@La-oxalate complex was prepared by a simple one-pot coprecipitation method at room temperature, where oxalate has been used as an organic ligand, and the carbonaceous biomass has been used as a doping material that is naturally a carboxylate-rich functional group derived from a sucrose biomass. In addition to SPC@La-oxalate, bare-SPC, La(OH)3, and SPC@La(OH)3 were also prepared via simple base-addition conventional methods, and their performances in AsO43– removal were compared. The FTIR peak at 848 cm–1 confirmed the presence of AsO43– on the SPC@La-oxalate complex after adsorption of 1 mM AsO43–. The high resolution X-ray photoelectron spectrum for the AsO43– adsorbed SPC@La-oxalate showed a peak at EB[As 3d] = 4...

Effect of lanthanum and chlorine doping on strontium titanates for the electrocatalytically-assisted oxidative dehydrogenation of ethane

Abstract: Oxidative dehydrogenation (ODH) of alkanes is an important catalytic reaction that can be used to convert less valuable alkanes, such as ethane, to more valuable olefins, such as ethylene. However, further oxidation of olefins to carbon dioxide and carbon monoxide limits the selectivity of the process. Oxide ion-conducting electrolyte reactors allow for controlling oxygen availability to the reaction and thus, improve the selectivity for olefin formation. In this study, strontium titanate-type perovskites were tested as anode catalysts for electro ODH reaction. Cl-incorporated, La-doped strontium titanates were synthesized via a modified Pechini route. The effect of lanthanum doping and chlorine incorporation on these catalysts was investigated. The characteristics of the catalysts were examined using ambient and in-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed oxidation (TPO) using CO2, laser Raman spectroscopy, and electrical conductivity measurements. In addition, impedance measurements were also taken to better understand the cell characteristics and resistances. Electrocatalytically-assisted ODH tests on the cell with La0.2Sr0.8TiO3±dClσ anode showed that ethane conversion and ethylene production rates increase with increasing current. It was also observed that La doping increases the electrical conductivity and ethane conversion, while Cl doping increases both ethane conversion and ethylene selectivity.

Lanthanum loaded graphitic carbon nitride nanosheets for highly sensitive and selective fluorescent detection of iron ions

Abstract: A facile synthesis of lanthanum (La) loaded graphitic carbon nitride nanosheets (CNNS) was developed in this study. The obtained La-CNNS exhibited an intense emission peak at 255 nm, owing to fluorescence enhancement effect of introduced La on the surface of CNNS. La-CNNS showed excitation-independent behavior and blue shift compared with CNNS. It displayed great fluorescence quenching via photoinduced electron transfer (PET) when a small amount of Fe3+ was added. The probe exhibited a wide linear response concentration range (0.1–20 μM) to Fe3+ with a detection limit of 0.0232 μM. The La-CNNS fluorescence probe was highly selective and suitable for Fe3+ analysis in natural water samples.