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31.
S. Colonna S. De Rossi M. Faticanti I. Pettiti P. Porta 《Journal of molecular catalysis. A, Chemical》2002,180(1-2):161-168
ZrO2-supported La, Co oxide catalysts with different La, Co loading (2, 6, 8, 12 and 16 wt.% as LaCoO3) were prepared by impregnation of tetragonal ZrO2 with equimolar amounts of La and Co citrate precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and BET specific surface area determination. Catalytic CO oxidation was performed at 298–800 K. XRD revealed the presence of tetragonal zirconia with traces of the monoclinic phase. LaCoO3 perovskite was also detected for loading higher than 6%. XAS experiments suggested that at high loading LaCoO3 and Co3O4 were formed, while at low loading, La, Co oxide species interacting with support, and hard to be structurally defined, prevailed. The catalysis study evidenced that the catalytic activity was due to segregated and highly dispersed cobalt oxide species. 相似文献
32.
Kjell Ove Kongshaug 《Journal of solid state chemistry》2004,177(6):1852-1857
The two organically pillared layered zinc hydroxides [Zn2(OH)2(ndc)], CPO-6, and [Zn3(OH)4(bpdc)], CPO-7, were obtained in hydrothermal reactions between 2,6-naphthalenedicarboxylic acid (ndc) and zinc nitrate (CPO-6) and 4,4′biphenyldicarboxylate (bpdc) and zinc nitrate (CPO-7), respectively. In CPO-6, the tetrahedral zinc atoms are connected by two μ2-OH groups and two carboxylate oxygen atoms, forming infinite layers extending parallel to the bc-plane. These layers are pillared by ndc to form a three-dimensional structure. In CPO-7, the zinc hydroxide layers are containing four-, five- and six coordinated zinc atoms, and the layers are built like stairways running along the [001] direction. Each step is composed of three infinite chains running in the [010] direction. Both crystal structures were solved from conventional single crystal data. Crystal data for CPO-6: Monoclinic space group P21/c (No. 14), a=11.9703(7), b=7.8154(5), c=6.2428(4) Å, β=90.816(2)°, V=583.97(6) Å3 and Z=4. Crystal data for CPO-7: Monoclinic space group C2/c (No. 15), a=35.220(4), b=6.2658(8), c=14.8888(17) Å, β=112.580(4)°, V=3033.8(6) Å3 and Z=8. The compounds were further characterized by thermogravimetric- and chemical analysis. 相似文献
33.
Yasuhiro Ono Ryuji IshikawaYuzuru Miyazaki Yoshinobu IshiiYukio Morii Tsuyoshi Kajitani 《Journal of solid state chemistry》2002,166(1):177-181
The layered oxide thermoelectric material β-Na0.67CoO2 has been studied by powder neutron diffraction, electric and magnetic measurements. This compound includes an edge-sharing CoO6 slab and a highly vacant Na+ sheet in a unit cell (space group symmetry C2/m, a=4.9023(4) Å, b=2.8280(2) Å, c=5.7198(6) Å and β=105.964(6)° at 300 K). The evaluated formal valence of cobalt ion, +3.33(1), is ascribed to the coexistence of Co3+ and Co4+ in the ratio 2:1. Polycrystalline β-Na0.67CoO2, a p-type thermoelectric material, exhibits metallic behavior of the electric resistivity below 300 K. The Curie-Weiss-type magnetic susceptibility indicates antiferromagnetic interactions between magnetic cobalt ions in the edge-sharing CoO6 slab. 相似文献
34.
固体氧化物电解池是一种高效、环境友好型的能量转换器件,可以直接将电能转化为化学能. 本文介绍了近年来作者课题组在固体氧化物电解池直接用于CO2还原的研究进展,并以阴极材料为主着重讨论了金属陶瓷电极和混合导电型钙钛矿氧化物电极的研究工作,最后展望了未来固体氧化物电解池直接电解CO2的研究思路和方向. 相似文献
35.
Presently, a large variety of layered materials are synthesized that are able to intercalate neutral guest molecules or to exchange inorganic and organic ions for interlayer ions. Several of these materials are also found as minerals.The intracrystalline reactivity of a few selected compounds will be described and compared to clay minerals:
相似文献
| - intercalation into crystalline silicic acids; |
| - reactions of phosphates, arsenates, and sulfates; |
| - reactions of titanates, niobates, and molybdates with long chain alkylammonium ions, and |
| - anion exchange properties of double hydroxides. |
36.
The temperature dependence of the paramagnetic susceptibility χm(T) taken in 2500 Oe, the resistivity ρ(T), and the thermoelectric power α(T) of DyBaCo2O5+x, which has Ba and Dy ordered into alternate (001) planes of an oxygen-deficient perovskite, have revealed a phase segregation in the compositional range 0.3?x<0.5. Orthorhombic DyBaCo2O5.51 has, in addition, oxygen vacancies ordered into alternate rows of the DyO0.51 (001) planes; a cold-pressed polycrystalline sample exhibits a first-order insulator-metal transition at TIM=320 K, a Curie temperature TC=300 K, and a broadened metamagnetic transition temperature TM≈265 K in 2500 Oe. A ferromagnetic M-H hysteresis curve fails to saturate at 5 T, and a minority ferromagnetic phase below TM has a volume fraction that decreases with decreasing temperature, vanishing below 50 K. Oxygen vacancies in the DyBaCo2O5.5 phase suppress the metallic state; interstitial oxygen does not. A thermoelectric power α(T)>0 of DyBaCo2O5.51 changing continuously across TIM is interpreted to manifest a metallic minority phase crossing a percolation threshold; α(T) also provides evidence for a progressive excitation of higher-spin Co(III) with increasing temperature from below 50 K to above TIM. A previous model of the RBaCo2O5.5 phase is extended to account for the Ising spin configuration below TC, the magnetic order in the presence of higher-spin octahedral-site Co(III), and the α(T) data. 相似文献
37.
38.
Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous. 相似文献
39.
Igor Presniakov Alexei Baranov Alexei Sobolev Viyacheslav Rusakov 《Journal of solid state chemistry》2007,180(11):3253-3261
For the first time a comparative study of rhombohedral LaNiO3 and LaCuO3 oxides, using 57Fe Mössbauer probe spectroscopy (1% atomic rate), has been carried out. In spite of the fact that both oxides are characterized by similar crystal structure and metallic properties, the behavior of 57Fe probe atoms in such lattices appears essentially different. In the case of LaNi0.99Fe0.01O3, the observed isomer shift (δ) value corresponds to Fe3+ (3d5) cations in high-spin state located in an oxygen octahedral surrounding. In contrast, for the LaCu0.99Fe0.01O3, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe4+(3d4) cations in octahedral coordination within Fe(IV) perovskite-like ferrates. To explain such a difference, an approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that in the case of LaNi0.99Fe0.01O3, electronic state of nickel is dominated by the d7 configuration corresponding to the formal ionic “Ni3+-O2−” state. On the other hand, in the case of LaCu0.99Fe0.01O3 a large amount of charge is transferred via Cu-O bonds from the O:2p bands to the Cu:3d orbitals and the ground state is dominated by the d9L configuration (“Cu2+−O” state). The dominant d9L ground state for the (CuO6) sublattice induces in the environment of the 57Fe probe cations a charge transfer Fe3++O−(L)→Fe4++O2−, which transforms “Fe3+” into “Fe4+” state. The analysis of the isomer shift value for the formally “Fe4+” ions in perovskite-like oxides clearly proved a drastic influence of the 4s iron orbitals population on the Fe−O bonds character. 相似文献
40.
Adachi K Sugiyama Y Yoneda K Yamada K Nozaki K Fuyuhiro A Kawata S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6616-6628
Novel triply hydrogen bonded suprastructures based on [M(tdpd)2(L)2]2- (H2tdpd=1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, L=solvent) and melamine-analogous cations have been synthesized and characterized. The use of anions containing two AAA sets from [M(tdpd)2(L)2]2- together with cations containing one DDD set (A=hydrogen-bond acceptor, D=hydrogen-bond donor) leads to the formation of complementary triply hydrogen bonded modules in the solid state. In all cases, the building module is further extended via additional hydrogen-bonding interactions to produce a tape, and tapes are assembled into sheets. These results show that a hydrogen-bonded module consisting of different kinds of building blocks, one of which is a metal complex that includes hydrogen-bond acceptor sites and the other is a hydrogen-bond donor molecule, will be attractive for constructing metal-containing supramolecular systems by the self-assembly technique. 相似文献