La Addition Research Articles

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by C-H and C-C bond activation of 1-pentene and 2-pentene.

La atom reactions with 1-pentene and 2-pentene are carried out in a laser-vaporization molecular beam source. The two reactions yield the same metal-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage of the pentene molecules. The dehydrogenated species La(C5H8) is the major product, whereas the carbon-carbon bond cleaved species La(C2H2) and La(C3H4) are the minor ones. La(C10H18) is also observed and is presumably formed by La(C5H8) addition to a second pentene molecule. La(C5H8) and La(C2H2) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species from the two reactions exhibit the same transitions. Adiabatic ionization energies and metal-ligand stretching frequencies are determined for the two species, and additional methyl bending and torsional frequencies are measured for the larger one. Five possible isomers are considered for La(C5H8), and a C1 metallacyclopentene (Iso A) is identified as the most possible isomer. La(C2H2) is confirmed to be a C2v metallacyclopropene. The ground electronic state of each species is a doublet with a La 6s1-based electron configuration, and ionization yields a singlet state. The formation of the lanthanacyclopentene includes La addition to the C=C double bond, La insertion into two C(sp3)-H bonds, and concerted dehydrogenation. For the 2-pentene reaction, the formation of the five-membered ring may also involve 2-pentene to 1-pentene isomerization. In addition to the metal addition and insertion, the formation of the three-membered metallacycle from 1-pentene includes C(sp3)-C(sp3) bond breakage and hydrogen migration from La to C(sp3), whereas its formation from 2-pentene may involve the ligand isomerization.

The Impact of La Doping on Dry Reforming Ni-Based Catalysts Loaded on FSP-Alumina

The activity of nickel-based catalysts makes them promising for the dry reforming of methane (DRM), but their implementation is limited by instability which stems from undesirable selectivity to side reactions that promote carbon formation. Cobalt can be added in the form of a bimetallic Ni–Co catalyst to improve stability although this can be at the expense of activity. Here we report the impact of lanthanum doping of an alumina support on the performance of neat Ni and bimetallic Ni–Co dry reforming catalysts with the intent of improving both stability/selectivity and activity. Direct investigation of the DRM side reactions demonstrated that introducing La to the alumina support decreased the selectivity of Ni towards the Boudouard and methane cracking reactions. This afforded Ni an enhanced resistance to catalyst coking, thereby improving catalyst stability. Monometallic Ni supported by La-doped alumina was found to be the most active catalyst for the DRM with the La addition also improving catalyst stability via suppression of the Boudouard and methane cracking reactions. The benefits of La-doping on catalyst performance were less pronounced when Co was present alongside the Ni as the La superseded the positive contribution of the Co. Characterisation of the materials illustrated La inclusion into the support was in the form of single atoms highly dispersed across the Al2O3 surface, which improved support basicity and strengthened the interactions between the Ni/Co metal and the support.

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)

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.

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by association and carbon-carbon bond cleavage of isoprene.

La atom reaction with isoprene is carried out in a laser-vaporization molecular beam source. The reaction yields an adduct as the major product and C-C cleaved and dehydrogenated species as the minor ones. La(C5H8), La(C2H2), and La(C3H4) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of all three species exhibit a strong origin band and several weak vibronic bands corresponding to La-ligand stretch and ligand-based bend excitations. La(C5H8) is a five-membered metallacycle, whereas La(C2H2) and La(C3H4) are three-membered rings. All three metallacycles prefer a doublet ground state with a La 6s1-based valence electron configuration and a singlet ion. The five-membered metallacycle is formed through La addition and isoprene isomerization, whereas the two three-membered rings are produced by La addition and insertion, hydrogen migration, and carbon-carbon bond cleavage.

Effect of La content and extrusion temperature on microstructure, texture and mechanical properties of Mg-Zn-Zr magnesium alloy

The microstructure, texture and mechanical properties of Mg-6wt%Zn-0.5 wt%Zr (ZK60) alloys with different La contents (0, 0.5 and 1 wt%) were investigated. The alloys were produced by low-pressure die casting and extruded at 300 °C and 400 °C, following homogenization at 400 °C for 24 h. La addition to ZK60 alloy resulted in a formation of Mg-Zn-La ternary phase, generating a semi-continuous network structure in their as-cast state. After extrusion, secondary phases were broken into fine particles distributed along the extrusion direction. These fragmented particles led to a nucleation of new grains around them i.e. particle stimulated nucleation (PSN), and promoted dynamic recrystallization (DRX) during extrusion. Therefore, increasing La content led to an increase in DRX fraction. Higher extrusion temperature resulted in larger DRXed grains and higher DRX fraction. The basal texture intensity was also decreased with increasing La addition and extrusion temperature by PSN mechanism and solute atoms of La. The ZK60-1La alloy extruded at 300 °C showed a superior yield strength of 311 MPa and ultimate tensile strength of 360 MPa as a result of significant grain refinement and dispersion strengthening. Increasing extrusion temperature resulted in a decrease in yield and ultimate tensile strengths and increase in ductility.

Influence of La addition on the semi-conductive properties of passive films formed on Cu-Ni alloy

The semi-conductive properties of passive films formed on Cu-Ni alloy and Cu-Ni-La alloy were investigated in 0.1 M NaOH solution, by employing electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis and point defect model (PDM). Results indicate that both the passive films formed on Cu-Ni alloy and Cu-Ni-La alloy display p-type semi-conductive characteristics with cation vacancies in order of magnitude of 1020 cm3. Compared with Cu-Ni alloy, La addition could significantly improve the corrosion resistance, due to a superior barrier passive film formed Cu-Ni-La alloy with a bigger film resistance (Rf), increased passive film thickness (Lss) in conjunction with decreased diffusion coefficient (D0).

Effect of Ca and RE additions on microstructures and tensile properties of AZ31 alloys

Microstructures and tensile properties of AZ31 magnesium alloys with the same amount of Ca and RE (Gd + La) additions are investigated. The results show that Al2Ca new phases form after adding Ca elements, Al2Gd and Al11La3 new phases form after adding Gd and La elements, and formations of Al-Ca and Al-RE phases could decrease Mg17Al12 phases and refine grains. Al2Ca and Al11La3 phases are crushed into granules because of severe deformation during hot extrusion, while Al2Gd phases are not. Room temperature (TR) and 150 °C (T150°C) tensile tests results reveal that both AZ31-1.5Ca and AZ31-1.5RE as-extruded alloys exhibit superior comprehensive tensile properties when compared to AZ31 as-extruded alloy, however, AZ31-1.5Ca as-extruded alloy could be a better choice in view of the costs. Textures images of as-extruded alloys indicate that 1.5 wt% Ca and RE additions affects little on textures of AZ31 as-extruded alloy, therefore, morphologies of second phases and average grain sizes are the leading cause of tensile properties of as-extruded alloys.

La, Rb and Ba Additions on the Effect of Oxygen Reduction in Molten Alkali Carbonates

In this study, the effects of La, Rb and Ba additions to (Li+Na)CO3 electrolyte were investigated using a half-cell and a coin-type MCFC. The effect of La and Rb on oxygen reduction on a gold electrode in a (Li+Na)CO3 melt at 650oC were examined using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The C 0 D 0 0.5 values determined from CV and EIS were not comparable. The addition of 0.5 mol% of La2O3 to (Li + Na)CO3 showed a remarkable increase in C 0 D 0 0.5 values determined by both EIS and CV analyses. The effect of La and Rb on cell performance of coin cells using (Li+Na)CO3 as electrolyte and operated at 650oC were examined using I-V curve. The total overpotential was decreased by 13% when 0.5 mol% of La2O3 was added to (Li + Na)CO3 electrolyte but was decreased by 9% when 3 mol% of Rb2CO3 was added to (Li + Na)CO3.

Microstructure and Hydrogen Absorption/Desorption Behavior of Mg23-xLa x Ni10 Alloy

Induction melting was used as a routine method to synthesize Mg23Ni10, Mg22LaNi10 and Mg21La2Ni10 alloys, and followed by a detailed microstructural characterization which included X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS), high resolution transmission electron microscope (HRTEM) and hydrogen absorption/desorption measurements. XRD analysis results showed that Mg2Ni and Mg phases were detected in the XRD pattern of the Mg23Ni10 alloy, however, the La addition results in conversion from Mg to LaMg3 and La2Mg17 phases and appearance of crystal defects included dislocations, twin grain boundary and vacancy in the Mg22LaNi10 and Mg21La2Ni10 alloy textures. The total maximum hydrogen absorption capacity was 4.45wt% for the Mg23Ni10 alloy, however, the Mg22LaNi10 and Mg21La2Ni10 alloys with vacancy, dislocations and twin grain boundary, absorbed 3.66wt% and 3.60wt%, respectively, indicating that the La addition led to decreasing of the maximum hydrogen absorption capacity. Besides, hydrogen absorption/desorption of 90% of saturated state expended for about 456 and 990 s for pristine Mg23Ni10 alloy, by contrast, the time decreased owing to improvement of hydrogen absorption and desorption kinetics in the alloy with La element, with which the uptake time for hydrogen content to 90% of saturated state was 150 and 78 s, and 90% hydrogen can be released in 930 and 804 s for Mg22LaNi10 and Mg21La2Ni10 alloys in the experimental condition.

Effects of Ti and La Additions on the Microstructures and Mechanical Properties of B-Refined and Sr-Modified Al–11Si Alloys

The effects of Ti and La additions on the microstructures and mechanical properties of B-refined and Sr-modified Al–11Si alloys were investigated in the present work. The interactions among Ti, La, B and Sr elements were discussed employing microstructure observation, thermal analysis and tensile test, respectively. It was found that the addition of 0.05 wt% B induces a transformation of eutectic Si from finely fibrous to coarsely plate-like morphology in the Al–11Si alloy with 0.02 wt%Sr modification, owing to the poisoning of IIT mechanism, and the eutectic Si grows only with TPRE mechanism. Both titanium and lanthanum can neutralize the co-poisoning effect between Sr and B in the Al–11Si alloy, but the neutralizing effect of La is dependent on the addition sequence. The combinative addition of La and B elements promotes the effective refinement of α-Al grains, but an inhomogeneous modification of eutectic Si phases is also observed, leading to a slightly decrease in the elongation.

Microstructure and properties of as-cast Cu-Cr-Zr alloys with lanthanum addition

Cu-0.45Cr-0.2Zr-xLa (x = 0–0.48) alloys were prepared by vacuum casting. The effects of La addition and orientation on the microstructure and properties of the as-cast alloy were investigated by an optical microscope, a scanning electron microscope with an energy dispersive X-ray spectrometer, a tensile testing machine and an electrical conductivity tester. The result shows that the addition of La significantly refines the columnar grainsize and decreases the secondary dendrite arm spacing. Trace addition of La improves the room temperature ultimate tensile strength, elongation and electrical conductivity mainly by purifying during melting and casting. The ultimate tensile strength, elongation and electrical conductivity significantly decrease with the increase of La content due to formation of coarse particles and oxides, which severely harm the performance of the Cu-0.45Cr-0.2Zr-xLa alloys. The Cu-0.45Cr-0.2Zr-0.13La alloy possesses a good combination of room temperature ultimate tensile strength, elongation and electrical conductivity. In addition, room temperature ultimate tensile strength and electrical conductivity along transverse direction of the ingot are higher than that along longitudinal direction, which is mainly ascribed to different distribution of grain boundary and grain orientation.

Effect of La Addition on the Electrical Characteristics and Stability of Solution-Processed LaInO Thin-Film Transistors With High-${k}$ ZrO2Gate Insulator

In this paper, solution-processed ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films are used to be as insulting layers for lanthanum indium oxide (LaInO) thin-film transistors (TFTs) with different La doping contents. The influence of La addition on the electrical properties and stability under bias stress and temperatures stress for LaInO TFTs is investigated in detail. With the improvement of La doping contents, the saturation mobility (μ) decreases from 48.8 to 32.7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> · V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and the threshold voltage (VT) increases from 1.12 to 1.76 V. When La doping concentration is 10 mol%, LaInO TFT has a small subthreshold swing of 0.12 V/dec. Meanwhile, the stability is improved obviously. It is attributed to the strong bonding strength of La-O relative to that of In-O, resulting in the reduction of trap states. X-ray photoelectron spectroscopy shows that the generation of oxygen vacancies can effectively be suppressed by La addition. The calculation of density of states and the measurement of the capacitance-voltage can also further confirm that the density of trap states is decreased by La addition, and thus the stability of LaInO TFTs can get an obvious improvement.

Lanthanum-mediated dehydrogenation of butenes: Spectroscopy and formation of La(C4H6) isomers.

La atom reactions with 1-butene, 2-butene, and isobutene are carried out in a laser-vaporization molecular beam source. The three reactions yield the same La-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage and coupling of the butenes. The dehydrogenated species La(C4H6) is the major product, which is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectrum of La(C4H6) produced from the La+1-butene reaction exhibits two band systems, whereas the MATI spectra produced from the La+2-butene and isobutene reactions display only a single band system. Each of these spectra shows a strong origin band and several vibrational progressions. The two band systems from the spectrum of the 1-butene reaction are assigned to the ionization of two isomers: La[C(CH2)3] (Iso A) and La(CH2CHCHCH2) (Iso B), and the single band system from the spectra of the 2-butene and isobutene reactions is attributed to Iso B and Iso A, respectively. The ground electronic states are 2A1 (C3v) for Iso A and 2A' (Cs) for Iso B. The ionization of the doublet state of each isomer removes a La 6s-based electron and leads to the 1A1 ion of Iso A and the 1A' ion of Iso B. The formation of both isomers consists of La addition to the C=C double bond, La insertion into two C(sp3)-H bonds, and H2 elimination. In addition to these steps, the formation of Iso A from the La+1-butene reaction may involve the isomerization of 1-butene to isobutene prior to the C-H bond activation, whereas the formation of Iso B from the La+trans-2-butene reaction may include the trans- to cis-butene isomerization after the C-H bond activation.

Effect of the Addition of Rare Earth Element La on the Tribological Behaviour of AlSi5Cu1Mg Alloy

The effects of 0, 0.3, 0.6 and 0.9 wt % modifier La on the dry sliding wear behaviours of AlSi5Cu1Mg alloy were investigated under different friction conditions (normal loads, sliding velocities) by using pin-on-disc configuration. The microhardness of the alloys was tested, and it was found that the microhardness of the alloys was improved by the La addition. The AlSi5Cu1Mg + 0.6 wt % La alloy exhibited the smallest grain size and maximum microhardness. The wear mechanism analysis of the worn surface was done, which drew support from a scanning electron microscope (SEM) that was equipped with an energy dispersive spectrometer. The results showed that AlSi5Cu1Mg + 0.6 wt % La alloy exhibited the best wear resistance, which was mainly due to the modified grain and microhardness. At the sliding velocity of 0.19 m/s, the adhesive wear became the main wear mechanism with the increase of the load because of the rupture of the oxide layer on the friction surface. Under the load of 3.8 MPa, the abrasive wear became slight as the sliding velocity increasing, due to the recrystallization phenomenon that happened in the frictional surface.

Maillard Conjugation of Sodium Alginate to Whey Protein for Enhanced Resistance to Surfactant-Induced Competitive Displacement from Air-Water Interfaces.

Whey protein adsorbed to an interface forms a viscoelastic interfacial film but is displaced competitively from the interface by a small-molecule surfactant added afterward. The present study evaluated the impact of the covalent conjugation of high- or low-molecular-weight sodium alginate (HA or LA) to whey protein isolate (WPI) via the Maillard reaction on the ability of whey protein to resist surfactant-induced competitive displacement from the air-water interface. Surfactant added after the pre-adsorption of conjugate to the interface increased surface pressure. At a given surface pressure, the WPI-LA conjugate showed a significantly higher interfacial area coverage and lower interfacial film thickness compared to those of the WPI-HA conjugate or unconjugated WPI. The addition of LA to the aqueous phase had little effect on the interfacial area and thickness of pre-adsorbed WPI. These results suggest the importance of the molecular weight of the polysaccharide moiety in determining interfacial properties of whey protein-alginate conjugates.

Improvement of a Mesh-Type Cu/Ni/γ-Al2O3/Al Catalyst for Steam Reforming of Dimethyl Ether by Metal (Fe, Zn or La) Addition for CO in Situ Removal

A mesh-type structured anodic alumina supported Cu/Ni bi-functional catalyst was developed for steam reforming of dimethyl ether (SRD). It was found that the Cu/Ni/γ-Al2O3/Al catalyst had remarkable catalytic activity and stability, but a high CO selectivity. Therefore, a multi-functional catalyst was proposed by metals (Fe, Zn, or La) addition to inhibit CO formation during the SRD process. The results show that promoter Fe can improve the Cu dispersion and decrease the reduction temperature of catalyst, and CO selectivity was minimized from 27% to around 3%. However, the addition of Zn and La only can decrease the CO selectivity to 12%. Furthermore, there was an excellent synergetic effect between Cu/Ni/γ-Al2O3 and Fe over the Cu/Ni/Fe/γ-Al2O3/Al catalyst by evaluating catalytic performance of catalysts with different packing structures. And the synergetic mechanism of the active components (γ-Al2O3, Cu or Cu2O, and Fe3O4) for SRD and CO in suit removal was proposed. Finally, a 400-h durability test was carried out and the results show that the Cu/Ni/Fe/γ-Al2O3/Al catalyst had an excellent stability with a 100% DME conversion and low CO selectivity.

Investigation on the modification behavior of A356.2 alloy with Yb–La composite modifier

In this work, an investigation was conducted to evaluate the influence of the Yb + La addition on the microstructures and mechanical properties of A356.2 alloy. The results show that the the grain size was refined and morphological structure of Si changed from needle-like to fine spheroidal particle by adding Yb + La. The eutectic temperature decreased from 589 °C to 581 °C and the freezing range of primary α-Al become wider after adding Yb + La. The mechanical properties showed great improvement after T6 heat treatment. The ultimate tensile strength and microhardness of the composites were increased to 279.0 MPa and 99.2 HB after T6 heat treatment which increased by 28.2% and 47.3%, respectively. The fracture mechanism was analyzed using the scanning electron microscopy and proved to be a transgranular/intergranular fracture modes.

Microstructure and properties of TP2 copper tube with La microalloying by horizontal continuous casting

The TP2 copper tube was prepared with La microalloying by horizontal continuous casting (HCC). The absorptivity of La and its effects on microstructure, tensile and corrosion properties of HCC TP2 copper tube were studied by means of the inductively coupled plasma optical emission spectrometer (ICP-OES), optical microscope (OM), scanning electron microscope (SEM) and potentiodynamic polarization measurements. The results show that the absorptivity of La in the HCC TP2 copper tube is about 15% under antivacuum conditions due to the good chemical activities of La. The impurity elements in copper tube such as O, S, Pb and Si can be significantly reduced, and the average columnar dendrite spacing of the copper tube can also be reduced from 2.21 mm to 0.93 mm by adding La. The ultimate tensile strength and the elongation with and without La addition are almost unchanged. However, the annual corrosion rate of the HCC TP2 copper tube is reduced from 10.18 mm•a-1 to 9.37 mm•a-1 by the purification effect of trace La.

Effect of Successive Multiple Doping of La, Nb and Fe on Structure and Lattice Vibration of MPB PZT

Morphotropic phase boundary (MPB) Lead zirconate titanate [i.e Pb(Zr0.52Ti0.48)O3, PZT] is modified by incorporation of i) La in Pb-site, ii) simultaneously La in Pb-site and Nb in Zr/Ti site and iii) simultaneously La in Pb-site, Nb and Fe in Zr/Ti-site. Samples are prepared by alkoxide sol-gel synthesis. XRD study reveals peak shift towards lower 2θ upon La addition but the shift is towards higher 2θ for both La and Nb are incorporated. Addition of Fe makes peak shift towards higher angle but the amount of shift is very small with respect to that of La and Nb doping. The XRD data is further analyzed with the help of Rietveld refinement which reveals change in lattice parameters. It is observed that successive doping of La, La-Nb and La-Nb-Fe decrease both lattice parameters a and c.However, for the case of Nb and La co-doped PZT the value of c increases with respect to the c of only La doped PZT. The charge difference in Nb (5+) and Fe (3+) ions have compensating effect as they are doped in the same atomic site (i.e. B-site of the ABO3) which is having charge 4+. Raman spectroscopic study reveals more complex effect of successive multiple doping of La, Nb and Fe. Some of the observations in Raman spectroscopy are supportive to the observations made in XRD. Raman spectra are analyzed by cumulative fitting of de-convoluted peaks, which represent various individual vibrational modes: reveal changes happening in the lattice due to the systematic successive doping of La, Nb and Fe.

Mechanical Properties and Corrosion Behavior of As-Cast Mg-Zn-Zr-(La) Magnesium Alloys

The effects of La content on the mechanical properties and corrosion behavior of as-cast Mg-Zn-Zr (ZK) magnesium alloys were investigated. The results showed that La addition to ZK60 alloy resulted in a considerable grain refinement and an increase in the volume fraction of second phases by formation of Mg-Zn-La ternary phase. The tensile tests were performed at both room and elevated temperatures. At room temperature, the yield and tensile strengths and elongation-to-fracture significantly increased with 0.2 wt.% La addition, then deteriorated slightly with increasing La additions above 0.2 wt.%. At 200 °C, the yield and tensile strengths continually improved and elongation-to-fracture decreased with increasing La content due to the presence of thermally stable Mg-Zn-La phase. Immersion and electrochemical corrosion tests revealed that the formation of Mg-Zn-La phases led to a higher amount of cathodic sites and preferential corrosion propagation, and thus a decrease in the corrosion resistance of ZK60 alloys.