Influence of60Co gamma radiation on La2CuO4 catalyst for the decomposition of hydrogen peroxide

The catalytic activity of La₂CuO₄ for the decomposition of H₂O₂ was studied in detail. La₂CuO₄ was prepared by the ceramic method in four different ways. Gamma irradiation of the La₂CuO₄ samples increased their catalytic activity irrespective of the method of preparation. The enhanced catalytic activity is attributed to irradiation generated Cu⁺ centres on the surface of the catalyst.     

Über Oxocuprate. XV Zur Kristallstruktur von Seltenerdmetalloxocupraten: La2CuO4, Gd2CuO4

About Oxocuprates. XV. The Crystal Structure of Rare Earth Oxocuprates: La₂CuO₄, Gd₂CuO₄ Gd₂CuO₄ and La₂CuO₄ are examined by single crystal X-ray methods. Gd₂CuO₄ is isotypic with Nd₂CuO₄, La₂CuO₄ however shows a slightly distorted K₂NiF₄ structure. Cu²⁺ has square (Gd₂CuO₄) or octahedral (La₂CuO₄) coordination. La₂CuO₄ is the only compound in the system of Rare Earth cuprates with K₂NiF₄-type structure.     

Über Oxocuprate. XVIII. Zur Kenntnis von Sr2CuO2Br2 mit einem Beitrag über La2NiO4

About Oxocuprates. XVIII. On Sr₂CuO₂Br₂ and a Contribution about La₂NiO₄ Sr₂CuO₂Br₂ (A) and La₂NiO₄ (B) were prepared and investigated by single crystal X-ray technique. (A) is isotypic with Sr₂CuO₂Cl₂, (B) with K₂NiF₄. Both compounds crystallize in the space group D–I4/mmm with the lattice constants (A): a = 399.1, c = 1 713.6 pm, (B): a = 387.6, c = 1 268.3 pm. A discussion about the octahedral distortion of Cu²⁺ and Ni²⁺ respectively in respect to other isotypic compounds is given.     

On the Crystal Structure of LaCaCuGaO5

The crystal structure of LaCaCuGaO₅ has been investigated by single crystal X-ray analysis. It crystallizes with orthorhombic symmetry, space group C–Ima2, a = 15.8467, b = 5,5077, c = 5.3188 Å, Z = 4. LaCaCuGaO₅ belongs to the mineral Brownmillerite showing layers of corner connected CuO₆ octahedra linked by GaO₄ tetrahedra. The La³⁺ and Ca²⁺ ions are distributed statistically over one crystallographic point position.     

A study on methanol steam reforming to CO2 and H2 over the La2CuO4 nanofiber catalyst

The La₂CuO₄ crystal nanofibers were prepared by using single-walled carbon nanotubes as templates under mild hydrothermal conditions. The steam reforming of methanol (SRM) to CO₂ and H₂ over such nanofiber catalysts was studied. At the low temperature of 150 °C and steam/methanol=1.3, methanol was completely (100%, 13.8 g/h g catalyst) converted to hydrogen and CO₂ without the generation of CO. Within the 60 h catalyst lifespan test, methanol conversion was maintained at 98.6% (13.6 g/h g catalyst) and with 100% CO₂ selectivity. In the meantime, for distinguishing the advantage of nanoscale catalyst, the La₂CuO₄ bulk powder was prepared and tested for the SRM reaction for comparison. Compared with the La₂CuO₄ nanofiber, the bulk powder La₂CuO₄ showed worse catalytic activity for the SRM reaction. The 100% conversion of methanol was achieved at the temperature of 400 °C, with the products being H₂ and CO₂ together with CO. The catalytic activity in terms of methanol conversion dropped to 88.7% (12.2 g/h g catalyst) in 60 h. The reduction temperature for nanofiber La₂CuO₄ was much lower than that for the La₂CuO₄ bulk powder. The nanofibers were of higher specific surface area (105.0 m²/g), metal copper area and copper dispersion. The in situ FTIR and EPR experiments were employed to study the catalysts and catalytic process. In the nanofiber catalyst, there were oxygen vacancies. H₂-reduction resulted in the generation of trapped electrons [e] on the vacancy sites. Over the nanofiber catalyst, the intermediate H₂CO/HCO was stable and was reformed to CO₂ and H₂ by steam rather than being decomposed directly to CO and H₂. Over the bulk counterpart, apart from the direct decomposition of H₂CO/HCO to CO and H₂, the intermediate H₂COO might go through two decomposition ways: H₂COO=CO+H₂O and H₂COO=CO₂+H₂.     

Reactivity of binary mixtures of Cu(II) oxalate and La(III) oxalate

Reactivity of binary mixtures of oxalates of Cu(II) and La(III) was studied by observing their thermal behaviours in decomposition using TG, DTA and XRD techniques to set the temperature conditions for preparations of various composites of oxides of Cu(II) and La(III). In the thermal behaviour it was found that the decomposition of Cu(II) oxalate is not affected while that of La(III) oxalate is drastically affected in the case of all the mixtures. The decomposition temperature at which La(III) oxide is formed is lowered by 250 K in the case of all the mixtures while the complete decomposition occurred at 723 K only in the case of mixtures containing excess Cu(II) oxalate.At 823 K La₂CuO₄ phase is developed in all the mixtures while -La and Cu₂La phases are also detected in mixtures containing excess Cu(II) oxalate. Therefore, the temperature 823 K was found to be suitable to prepare various composites viz. La₂CuO₄, La₂CuO₄·La₂O₃ and La₂CuO₄·CuO to study their electrical properties.Authors are thankful to the authorities of Department of Atomic Energy (DAE), Government of India, for providing the funds for research project and to Professor A. V. Phadke, Department of Geology, University of Poona, for valuable discussion.     

Synthesis and Structure of Sr1-xLixCuO2 (0<x<:0.15) Phases Produced at High Temperatures and Pressures

We studied the possibility of synthesizing infinitelayer (IL) phases of Sr_1-xLi_xCuO₂ (01-xLi_xCuO₂ (0 < x < 1) solid solutions and from the corresponding cuprates, SrCuO₂ and Li₂CuO₂, at high pressures (P = 4–8 GPa) and high temperatures (T = 600–1000°). The optimal conditions for synthesis of the IL phases are P = 4 GPa, T = 800°gr, and = 2 min. At high pressures and temperatures, the components of the SrCuO₂–LiCuO₂ system show limited mutual solubility. Sr_1-xLi_xCuO₂ solid solutions exist at 0 < x < 0.15. The relationship between the unit cell parameters and Li content of highpressure Sr_1-xLi_xCuO₂ phases has been established.     

The direct decomposition of NO over the La2CuO4 nanofiber catalyst

The NO catalytic direct decomposition was studied over La₂CuO₄ nanofibers, which were synthesized by using single walled carbon nanotubes (CNTs) as templates under hydrothermal condition. The composition and BET specific surface area of the La₂CuO₄ nanofiber were La₂Cu_0.88²⁺Cu_0.12⁺O_3.94 and 105.0 m²/g, respectively. 100% NO conversion (turnover frequency-(TOF): 0.17 g_NO/g_catalyst s) was obtained over such nanofiber catalyst at temperatures above 300 °C with the products being only N₂ and O₂. In 60 h on stream testing, either at 300 °C or at 800 °C, the nanofiber catalyst still showed high NO conversion efficiency (at 300 °C, 98%, TOF: 0.17 g_NO/g_catalyst s; at 800 °C, 96%, TOF: 0.16 g_NO/g_catalyst s). The O₂ and NO temperature programmed desorption (TPD) results indicated that the desorption of oxygen over the nanofibers occurred at 80-190 and 720-900 °C; while NO desorption happened at temperatures of 210-330 °C. NO and O₂ did not competitively adsorb on the nanofiber catalyst. For outstanding the advantage of the nanostate catalyst, the usual La₂CuO₄ bulk powder was also prepared and studied for comparison.     

Crystal structure of the La3+ sandwich complex based on 8-membered macrocyclic siloxanolate ligands

The product of the reaction between anhydrous lanthanum trichloride and potassium vinylsiloxanolate, K₅[VinSiO₂]₈La₄(₄-OH)[O₂SiVin]₈ · 5n-BuOH·2H₂O has been studied by X-ray diffraction. The compound is a «sandwich»-type complex where macrocyclic vinyloctasiloxanolate ligands with regularcis-configuration have co-axial and antiparallel orientation. These ligands coordinate a planar «cationic layer» formed by four La³⁺ ions and stabilized by an additional ₄-OH^– bridge ligand. A three-dimensional cage structure of complex lanthansiloxanolate pentaanions linked through the coordinated K⁺ counter-ions is formed in the crystal studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 184–189, January, 1993.     

Reactivity of oxalates of La(III), Ba(II) and Cu(II) in ternary mixtures

Composites of cuprates of La(III) and Ba(II) were obtained by decomposing mixtures of oxalates of La(III), Ba(II) and Cu(II) prepared in 111 and 123 mol proportions respectively and sintering the oxide products at 1173 K. Reactions studied by TG, DTA and XRD techniques revealed the following features: (i) Decomposition of oxalates of La(III) and Ba(II) is drastically affected in mixtures. Decomposition temperature of organic part in the former (111) is shifted by 100 K while that of BaCO₃ in the case of latter (123) is shifted by 400 K towards lower temperature side. (ii) All exothermic peaks on DTA traces of both the mixtures are allotted to the decomposition of oxalates to Cu₂O, La₂O₂CO₃ and BaCO₃ phases while endothermic peaks around 863 and 1083 K are assigned for BaCuO₂ and La₂CuO₄ phases respectively in the case of former (111) and endothermic peaks at about 1068, 1136 and 1213 K are correlated with BaCuO₂, a composite of La₂O₃, La₂CuO₄ and La_0.5Ba_0.5CuO_3– (0.5) phases and LaBa₂Cu₃O_7– (0) phase respectively in the case of latter (123) and (iii) Lines of all cuprate compounds appear in XRD patterns of those samples preheated at temperatures 873 K. The following reaction is proposed in the case of 123 mixture: Authors are deeply thankful to the Authorities of Department of Atomic Energy (DAE), Goverment of India, for providing the funds for research project and to Professor A. V. Phadke, Department of Geology, University of Poona, for the valuable discussion.     

Surface composition in perovskite-like cuprates as probed by X-ray photoelectron spectroscopy

Complex cuprates La_0.85Sr_0.15CuO_2.5?δ having an anion-deficient perovskite structure and La_2?x Sr _x CuO_4?δ (x = 0.15, 0.6, 1.0) having a K₂ NiF₄ layered structure have been prepared by ceramic technology. X-ray powder diffraction verified that single-phase samples were obtained. X-ray photoelectron spectroscopy (XPS) was used to determine the surface composition of compacted samples. It was found that both the photoionization cross-section and the photoelectron mean free path should be taken into account when calculating the surface composition. The surface was enriched in strontium as a result of segregation, regardless of the bulk composition of the cuprate sample.     

Prediction of transport properties of new functional materials based on lanthanum-strontium cuprates: Molecular mechanics calculations

The method of molecular dynamics is used for prediction of properties of new functional materials based on lanthanum-strontium cuprates La_{2 ? x} Sr _x CuO_{4 ? δ} as new materials of the solid state ionics. The most interesting phases are synthesized to test the obtained calculation data and their electrophysical and thermomechanical characteristics are studied. It is shown that the high values of the oxygen diffusion coefficients are obtained in the La_{2 ? x} Sr _x CuO_{4 ? δ} solid solutions with a high replacement degree of Sr → La (up to x = 1). The calculated values of lattice cell parameters, thermal expansion coefficients and oxygen diffusion coefficients agree with the experimental data. The observed anisotropy of anionic transport for all the studied compositions corresponds to the regularities of crystal structure of complex oxides. Using the molecular dynamics method allows tracing the contribution of separate types of oxygen ions (equatorial and apical) into ionic transport at the microscopic level and also confirming directly that oxygen diffusion occurs according to the usual jump mechanism, mainly in (CuO₂) layers.     

Über ternäre Oxocuprate. VII. Zur Kristallstruktur von Nd2CuO4

About Oxocuprates. VII. On the Crystal Structure of Nd₂CuO₄ The crystal structure of Nd₂CuO₄ was examined by single crystal X-ray diffraction data (Space group D—I4/mmm, a = 3.945, c = 12.171 Å) Nd₂CuO₄ has not the K₂NiF₄-type but forms a hitherto unknown crystal structure with Cu²⁺ in a complanar oxygen surrounding similar to the CaF₂-structure. A detailed discussion is given.     

The in situ study of surface species and structures of oxide-derived copper catalysts for electrochemical CO2 reduction

Oxide-derived copper (OD-Cu) has been discovered to be an effective catalyst for the electroreduction of CO₂ to C2+ products. The structure of OD-Cu and its surface species during the reaction process are interesting topics, which have not yet been clearly discussed. Herein, in situ surface-enhanced Raman spectroscopy (SERS), operando X-ray absorption spectroscopy (XAS), and ¹⁸O isotope labeling experiments were employed to investigate the surface species and structures of OD-Cu catalysts during CO₂ electroreduction. It was found that the OD-Cu catalysts were reduced to metallic Cu(0) in the reaction. CuO_x species existed on the catalyst surfaces during the CO₂RR, which resulted from the adsorption of preliminary intermediates (such as *CO₂ and *OCO⁻) on Cu instead of on the active sites of the catalyst. It was also found that abundant interfaces can be produced on OD-Cu, which can provide heterogeneous CO adsorption sites (strong binding sites and weak binding sites), leading to outstanding performance for obtaining C2+ products. The Faradaic efficiency (FE) for C2+ products reached as high as 83.8% with a current density of 341.5 mA cm⁻² at −0.9 V vs. RHE.

CuO_x species were shown to exist on OD-Cu during the CO₂RR, which resulted from the adsorption of preliminary intermediates (such as *CO₂ and *OCO⁻) on Cu instead of on the active sites of the catalyst.     

Suppression of superconductivity in submicron La1.85Sr0.15CuO4?δ

Bulk La_1.85Sr_0.15CuO_4– (LSCO) superconducts below 36K. But microcrystalline LSCO with mean particle size 700nm (prepared by rapid liquid dehydration) is not superconducting down to 4.2K. This may be due to a size-induced structural distortion and an accompanying reduction in the oxygen occupancy.     

Electron-irradiation induced phase transformation in La1/3Zr2(PO4)3: La displacement in a preserved NASICON framework

The La_1/3Zr₂(PO₄)₃ NASICON-type compound (S.G. - neutron and X-ray diffraction experiments) is investigated by transmission electron microscopy (TEM) technique, selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM), in order to study locally the lanthanum distribution. An irreversible structural transformation is observed, without modification of the atomic content and cell size, as soon as the phase is illuminated by the electron beam. The progressive disappearance of the spots which do not check the R conditions on the SAED patterns is clearly shown along two zone axis, [001] and [100]. This transformation implies the displacement of the two La³⁺ cations in a preserved classical [Zr₂(PO₄)₃]⁻ network. This interesting behavior is in good agreement with the La³⁺ ionic conductivity observed in La_1/3Zr₂(PO₄)₃ (4.09×10⁻⁷ S cm⁻¹ at 700 °C). To our knowledge, this is the first time that a complete TEM study is done on a NASICON-type phase.     

über Erdalkalimetalloxocuprate,VIII Zur Kenntnis von Sr2CuO2Cl2

On Alkaline Earth Oxocuprates VIII. About Sr₂CuO₂Cl₂ Sr₂CuO₂Cl₂ was prepared and investigated by single crystal X – ray work (space group D–Immm, a = 3.975, c = 15.618 Å). Sr₂CuO₂Cl₂ is isotypic with K₂NiF₄ – compounds and shows an octahedral configuration for Cu²⁺. Cl^? occupies trans-positions of the octahedral Cu²⁺/O^2? polyhedron. A discussion with related compounds (Sr₂CuO₃ and Nd₂CuO₄) explains the observed distribution of O^2? and Cl^?.     

Phase equilibria in the system La2O3-Na2O-P2O5

In the ternary system La₂O₃-P₂O₅-Na₂O the partial system La₂O₃-Na₄La₂P₄O₁₅-LaPO₄ has been examined by the thermal, dilatometric X-ray and microscopic analyses and its phase diagram provided. The lanthanum oxyphosphate La₃PO₇ melts incongruently at the 1590°C temperature and crystallizes in a monoclinic systema=11.20 Å,b=11.94 Å,c=7.01 Å,=93.79 andV=936.97 ų.

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Zusammenfassung Mittels Thermo- und dilatometrischer Analyse, Röntgendiffraktionsuntersuchungen und Mikroskopie wurde das Teilsystem La₂O₃ - Na₄La₂P₄O₁₅ - LaPO₄ des ternären Systemes La₂O₃ - P₂O₅ - Na₂O untersucht und ein Phasendiagramm entwickelt. Lanthanoxyphosphat La₃O₇ schmilzt inkongruent bei 1590°C und kristalliert in einem monoklinen System mita=11.20 Ä,b=11.94 Ä,c=7.01 Å,=93.79 undV=936.97 ų.

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The author thanks Mrs. B. Lagódka for the technical assistance (thermogravimetric analyses). The thermal study was supported by grant CPBP.     

Electrode properties of Sr doped La2CuO4 as new cathode material for intermediate-temperature SOFCs

High performance La_2−xSr_xCuO_4−δ (x = 0.1, 0.3, 0.5) cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFCs) were prepared and characterized. The investigation of electrical properties indicated that La_1.7Sr_0.3CuO₄ cathode has low area specific resistance (ASR) of 0.16 Ω cm² at 700 °C and 1.2 Ω cm² at 500 °C in air. The rate-limiting step for oxygen reduction reaction on La_1.7Sr_0.3CuO₄ electrode changed with oxygen partial pressure and measurement temperature. La_1.7Sr_0.3CuO₄ cathode exhibits the lowest overpotential of about 100 mV at a current density of 150 mA cm⁻² at 700 °C in air.