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101.
Effect of Copper Substitution and Preparation Methods on the LaMnO3 Structure and Catalysis of Methane Combustion and CO Oxidation 总被引:1,自引:0,他引:1
LaMn1-xCuxO3刡冊 perovskite oxides (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were prepared by two different methods, the Pechini and sol-gel methods. The catalysts were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray fluorescence spectroscopy, N2 adsorption, and temperature-programmed reduction. Their catalytic activity in the oxidation of methane and CO was evaluated. EDS and SEM results showed that the Pechini samples had more homogeneity and smaller particles (higher specific surface area). The catalytic activity for methane combustion was highest for x = 0.2. In CO oxidation, the oxides with x = 0.2 and x = 0.4 were the most active. The Pechini samples had higher activity and stability than the sol-gel samples. 相似文献
102.
A single phase rare earth double perovskite oxide Ba2CeNbO6 (BCN) is synthesized by solid-state reaction technique for the first time. The X-ray diffraction pattern of the sample at room temperature shows monoclinic structure, with the lattice parameters, a=5.9763 Å, b=5.975 Å and c=8.48 Å and β=90.04°. Impedance spectroscopy is used to study the ac electrical behavior of this material as a function of frequency (102-106 Hz) at various temperatures (30-450 °C). A relaxation is observed in the entire temperature range. Conduction mechanism is investigated by fitting the complex impedance data to Cole-Cole equation. Complex impedance plane plots show only one semicircular arc, indicating only the grain contribution of dielectric relaxation. The scaling behavior of imaginary part of electric modulus (M″) and imaginary part of electrical impedance (Z″) suggests that the relaxation describes the same mechanism at various temperatures. The frequency dependence of conductivity is interpreted in terms of the jump relaxation model and is fitted to Jonscher's power law. The values of dc conductivities extracted from the Jonscher power law varies from 2.79×10−7 to 3.5×10−5 Sm−1 with the increase in temperature from 100 to 450 °C. The activation energies (0.37 eV) extracted from M″(ω) and Z″(ω) peaks are found to follow the Arrhenius law. 相似文献
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106.
L. Patron O. Carp I. Mandru G. Grasa 《Journal of Thermal Analysis and Calorimetry》1999,56(2):597-602
New Nd-Co based polynuclear coordination compounds containing as ligand polyhydrocarboxylic acid as tartaric, malic and gluconic
acids were prepared, namely: [NdCo(tart)3]·4H2O, (NH4)[NdCo0.5Cu0.5(tart)3]·4H2O, (NH4)[NdCo(malic)3]·4H2O, (NH4)[NdCo0.5Cu0.5(malic)3]·4H2O, [NdCo(gluc)4]·4H2O and [Nd2CoCu(gluc)7]·5H2O. A comparison between the thermal behaviour of the studied polynuclear coordination compounds concerning thermal stability
and thermal decomposition stoichiometry was inferred. Oxalic and malonic intermediates were identified at about 300°C in the
thermal decomposition of tartaric and malic compounds. In all the decomposition processes at about 400°C the presence of oxocarbonate
is shown. The residual products are mixed oxides of perovskite type.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
107.
R. N. Pletnev É. I. Yurieva S. V. Verkhovskii G. V. Bazuev 《Journal of Structural Chemistry》2005,46(1):59-66
The 63Cu and 139La NMR spectra of the low-(δ = 0.25) and high-temperature (δ = 0) phases of lanthanum cuprate LACu0.81Ni0.19O2.5+δ have been obtained. Quantum chemical calculations of the electronic structure of the high-temperature phase have been performed. It is found that the observed metal-semiconductor phase transition is attended by changes in the degree of atomic ordering and in the character of electronic conductivity over certain types of “copper” centers. 相似文献
108.
Dr. Alessandra Alberti Dr. Ioannis Deretzis Dr. Giovanna Pellegrino Dr. Corrado Bongiorno Dr. Emanuele Smecca Dr. Giovanni Mannino Dr. Filippo Giannazzo Prof. Guglielmo Guido Condorelli Dr. Nobuya Sakai Prof. Tsutomu Miyasaka Dr. Corrado Spinella Dr. Antonino La Magna 《Chemphyschem》2015,16(14):3064-3071
We investigate the degradation path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temperature by means of X‐ray diffraction, spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI2. We describe how this degradation product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3NH2 or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material. 相似文献
109.
Dong‐Gyu Lee Ohhun Gwon Han‐Saem Park Su Hwan Kim Juchan Yang Prof. Sang Kyu Kwak Prof. Guntae Kim Prof. Hyun‐Kon Song 《Angewandte Chemie (International ed. in English)》2015,54(52):15730-15733
The electric conductivity‐dependence of the number of electrons transferred during the oxygen reduction reaction is presented. Intensive properties, such as the number of electrons transferred, are difficult to be considered conductivity‐dependent. Four different perovskite oxide catalysts of different conductivities were investigated with varying carbon contents. More conductive environments surrounding active sites, achieved by more conductive catalysts (providing internal electric pathways) or higher carbon content (providing external electric pathways), resulted in higher number of electrons transferred toward more complete 4e reduction of oxygen, and also changed the rate‐determining steps from two‐step 2e process to a single‐step 1e process. Experimental evidence of the conductivity dependency was described by a microscopic ohmic polarization model based on effective potential localized nearby the active sites. 相似文献
110.
《化学:亚洲杂志》2017,12(8):882-889
Ag0.5La0.5TiO3 with an ABO3 perovskite structure was synthesized by a newly developed ion‐exchange method. Molten Ag2SO4 instead of traditional molten AgNO3 was used as Ag+ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag+ for Na+ in Na0.5La0.5TiO3 with a stable ABO3 perovskite structure at a high ion‐exchange temperature (700 °C). Under full‐arc irradiation, the O2‐evolution activity of Ag0.5La0.5TiO3 was about 1.6 times that of Na0.5La0.5TiO3 due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag+ for Na+ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light‐response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag+ for Na+ induced a lattice distortion of the ABO3 perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible‐light irradiation, Ag0.5La0.5TiO3 displayed notable O2 evolution whereas Na0.5La0.5TiO3 showed little O2 evolution, thus demonstrating that the substitution of Ag+ for Na+ enabled the use of visible light to evolve O2 photocatalytically. This work presents an effective route to explore novel Ag‐based photocatalysts. 相似文献