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1.
Kuśtrowski P Chmielarz L Dziembaj R Cool P Vansant EF 《The journal of physical chemistry. A》2005,109(2):330-336
The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites. 相似文献
2.
高建平 《中国无机分析化学》2019,9(1):64-66
建立了一种用电感耦合等离子体发射光谱仪(ICP-AES)测定磷酸中金属元素的分析方法。实验结果表明:选择合适的样品前处理方式和优化的仪器操作条件,方法的检出限可达到0.0012 ug/g~0.0552ug/g、加标回收率达到95%~105%,满足实际样品分析要求。 相似文献
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Ndiaye B Bhat S Jouaiti A Berclaz T Bernardinelli G Geoffroy M 《The journal of physical chemistry. A》2006,110(31):9736-9742
Paramagnetic complexes M(CO)5P(C6H5)2, with M = Cr, Mo, W, have been trapped in irradiated crystals of M(CO)5P(C6H5)3 (M = Cr, Mo, W) and M(CO)5PH(C6H5)2 (M = Cr, W) and studied by EPR. The radiolytic scission of a P-C or a P-H bond, responsible for the formation of M(CO)5P(C6H5)2, is consistent with both the number of EPR sites and the crystal structures. The g and 31P hyperfine tensors measured for M(CO)5P(C6H5)2 present some of the characteristics expected for the diphenylphosphinyl radical. However, compared to Ph2P*, the 31P isotropic coupling is larger, the dipolar coupling is smaller, and for Mo and W compounds, the g-anisotropy is more pronounced. These properties are well predicted by DFT calculations. In the optimized structures of M(CO)5P(C6H5)2 (M = Cr, Mo, W), the unpaired electron is mainly confined in a phosphorus p-orbital, which conjugates with the metal d(xz) orbital. The trapped species can be described as a transition metal-coordinated phosphinyl radical. 相似文献
8.
Anoop Kelkar Amrit Prakash Mohd. Afzal J. P. Panakkal H. S. Kamath 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):595-601
A single-column ion chromatography (SCIC) for the simultaneous determination of alkali, alkaline earth and transition metal
elements in UO2, ThO2 powders and sintered (Th, U) O2 pellet is described in this paper. Metrosep cation 1-2 analytical column containing poly butadiene-maleic acid (PBDMA) coated
silica has been applied to the ion chromatographic separation of 12 cations (copper, lithium, sodium, ammonium, nickel, potassium,
zinc, cobalt, manganese, magnesium, calcium and strontium) using an isocratic elution with tartaric acid and oxalic acid as
mobile phase with non-suppressed conductivity detection. Mobile phase composition was optimized to 1 mM tartaric acid and
0.75 mM oxalic acid for the baseline separation of 12 cations. The calibration plots were linear in the range of 0.05–40 mg L−1 with regression coefficients better than 0.998. The relative standard deviations (RSDs) of the retention time, peak area
and peak height were less than 1, 2.8 and 3.0%, respectively. The recoveries of the spiked samples for the cations were 94–110%.
The method developed was validated by comparison with certified standards of UO2 and ThO2 powders. 相似文献
9.
A. V. Soudackov A. L. Tchougreeff I. A. Misurkin 《Theoretical chemistry accounts》1992,83(5-6):389-416
Summary A semiempirical effective Hamiltonian treatment is proposed for transition metal complexes, taking into accountd-electron correlations, weak covalency of the metal-ligand bonds and the electronic structure of the ligand sphere. The technique uses the variation wave function which differs from the usual Hartree-Fock antisymmetrized product of molecular orbitals extended over the whole complex. The scheme is implemented and parameters describing the metal-ligand interactions are adjusted to reproduced-d-excitation spectra of a number of octahedral MF
6
4–
(M=Mn, Fe, Co, Ni) anions, Mn(FH)
6
2+
cation, CoCl
6
4–
anion, and a tetrahedral CoCl
4
2–
anion. The values of the parameters are reasonable, thus confirming the validity of the proposed scheme. 相似文献
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Bishop MM Lindoy LF Parkin A Turner P 《Dalton transactions (Cambridge, England : 2003)》2005,(15):2563-2571
Pseudo-macrocyclic complexes of copper(II), and in one instance nickel(II), incorporating the bidentate ligands methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)imidocarbamate and N,N-dimethyl-N'-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)guanidine are reported and their X-ray structures compared with those previously reported for related complexes of two N-(4-oxo- 5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)alkanimidamides. A feature of these complexes is that they are capable of forming hydrogen bonded chains or chains in which adjacent complexes are linked by phenyl 'embraces'. Changes in supramolecular structure arising from small changes in ligand structure or on crystallisation from different solvents are also discussed. 相似文献
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É. A. Kravtsova G. K. Parygina L. N. Mazalov Yu. S. Shorikov 《Journal of Structural Chemistry》1990,31(4):658-661
Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 4, pp. 145–148, July–August, 1990. 相似文献
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Gérard Demazeau Bernard Buffat Michel Pouchard Paul Hagenmuller 《Journal of solid state chemistry》1984,54(3):389-399
The A′xA2?xLi0.5M0.5O4 matrix deriving from the K2NiF4 structure has an elongated MO6 octahedron; it has been used to stabilize anisotropic electronic configurations such as high-spin Fe4+, low-spin Co4+, medium-spin Co3+, low-spin Ni3+, or low-spin Cu3+. The choice of ions to be stabilized was based on a simple model for predicting the electronic configuration of a dn ion in a tetragonally distorted octahedral environment. 相似文献
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Rafael Bilbao María Benita Murillo Angela Millera Jos Francisco Mastral 《Thermochimica Acta》1991,190(2):163-173
An experimental system that allows the use of large particle sizes and the simulation of different operating conditions was built to study the thermal decomposition of lignocellulosic materials. The values of solid conversion and of temperature obtained at different points using spherical particles of pine wood 2 cm in diameter are shown. The conversion values are compared with those calculated from the equations obtained in a thermobalance for small particle sizes. 相似文献
15.
Caruntu D Remond Y Chou NH Jun MJ Caruntu G He J Goloverda G O'Connor C Kolesnichenko V 《Inorganic chemistry》2002,41(23):6137-6146
Study of the reactivity of 3d transition metal cations in diethylene glycol solutions revealed several key features that made it possible to develop a new method for synthesis of the nanocrystalline transition metal ferrites. The 3-7 nm particles of [MFe2O4]n[O2CR]m, where M = Mn, Fe, Co, Ni, and Zn, ligated on their surface with long-chain carboxylate anions, have been obtained in an isolated yield of 75-90%. The key features are the following. Complexation of the first-row transition metal cations with diethylene glycol at a presence of alkaline hydroxide is sufficient to enable control over the rate of their hydrolysis. The reaction of hydrolysis leads to the formation of metal oxide nanocrystals in colloidal solution. The nanoparticles growth is terminated by an added long-chain carboxylic acid, which binds to their surface and acts as a capping ligand. The isolated nanocrystalline powders are stable against agglomeration and highly soluble in nonpolar organic solvents. 相似文献
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The combined use of different synchrotron radiation (SR) X-ray diffraction techniques is shown to be effective in collecting the most complete structural information about an object being studied. The high intensity of SR and its spectral-angular distribution enable researchers to conduct experiments with high angular resolution, experiments using resonance effects, time-resolved experiments, and experiments where the sample is exposed to the effects of temperature and reaction medium. Results are presented of two studies where the distinctive features of SR play the key role. 相似文献
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Bimetallic catalysts have been prepared by successively modifying the high-silica zeolite ZSM-5 with cobalt and aluminum salts. The performance of these catalysts in the conversion of higher alkanes at medium temperatures (130–190°C) depends on whether the reaction is conducted in the liquid or gas phase. In both cases, the transition metal and surface-anchored aluminum chloride act synergetically. In the liquid-phase reactions of n-heptane and n-dodecane, the activity of the bimetallic systems is more than one order of magnitude higher than the activity of the hydrogen form of the initial zeolite. New adsorption and catalytic sites resulting from the introduction of the two modifiers into the zeolite have been discovered by diffuse reflectance IR spectroscopy. In particular, the modifiers generate a new state of cobalt in which the transition metal atoms are linked with aluminum atoms through chlorine or oxygen atoms. The liquid-phase conversion of alkanes over the modified zeolites is unlikely to proceed via a carbocationic mechanism. 相似文献
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The abundance of rare-earth elements (REE) and yttrium in geological materials is generally low, and most samples contain elements that interfere in the determination of the REE and Y, so a separation and/or preconcentration step is often necessary. This is often achieved by ion-exchange chromatography with either nitric or hydrochloric acid. It is advantageous, however, to use both acids sequentially. The final solution thus obtained contains only the REE and Y, with minor amounts of Al, Ba, Ca, Sc, Sr and Ti. Elements that potentially interfere, such as Be, Co, Cr, Fe, Mn, Th, U, V and Zr, are virtually eliminated. Inductively-coupled argon plasma atomic-emission spectroscopy can then be used for a final precise and accurate measurement. The method can also be used with other instrumental methods of analysis. 相似文献
19.
von Feilitzsch T Härter P Schiemann O Michel-Beyerle ME Steiner UE Gilch P 《Journal of the American Chemical Society》2005,127(43):15228-15235
The radical pair recombination of an intramolecular electron-transfer system containing a transition metal moiety has been addressed by femtosecond spectroscopy. The radical pair is formed by ultrafast electron transfer (90 fs) from a ferrocene residue to a photoexcited Nile blue moiety. Its recombination proceeds on the picosecond time scale in a multiexponential fashion. The kinetic pattern is a manifestation of spin processes competing with electron transfer. Magnetic field effects on these kinetics allow one to disentangle the two contributions. Their temperature dependencies yield the activation parameters of the two processes. The discussion focuses on the mechanism of electron spin relaxation. Strong evidence for the Orbach/Kivelson mechanism will be given. 相似文献
20.
A. A. El-Bindary I. S. Shehatta E. M. Mabrouk 《Monatshefte für Chemie / Chemical Monthly》1994,125(4):373-384
Summary Proton-ligand dissociation and metal-ligand stability constants of trithiocarbodiglycolic acid (TCGA) with some transition metal ions were calculated potentiometrically. The order of stability constants was found to be Fe3+ > Cu2+ > Ni2+ > Co2+. The effect of temperature on the stability of the complexes formed was studied and the corresponding thermodynamic functions were derived and discussed. Polarographic and cyclic voltammetric behaviours ofTCGA were investigated in B.R. buffer solutions ofpH 2–12. In solutions ofpH<8, the polarograms and cyclo-voltammograms exhibited a single 2-electron diffusion-controlled irreversible step, corresponding to the reduction of the C=S. The mechanism of the reduction process was postulated and the kinetic parameters of the electrode process were evaluated.
Thermodynamik der Komplexierung einiger Übergangsmetallionen mit Trithiocarbodiglykolsäure. Potentiometrische und voltammetrische Untersuchungen
Zusammenfassung Die Protonendissoziation vom Liganden und die Metall-Ligand-Stabilitätskonstanten von Trithiocarbodiglykolsäure (TCGA) mit einigen Übergangsmetallionen wurden potentiometrisch bestimmt. Die Reihung der Stabilitäten ist Fe3+ > Cu2+ > Ni2+ > Co2+. Die Temperaturabhängigkeit der Stabilitäten wurde gemessen und die entsprechenden thermodynamischen Funktionen abgeleitet. Das polarographische und cyclovoltammetrische Verhalten vonTCGA wurde in B.R.-Puffer beipH 2–12 ermittelt. In Lösungen vonpH<8 zeigten die Polarogramme und Cyclovoltagramme eine einzelne diffusionskontrollierte irreversible 2-Elektronen-Stufe, die der Reduktion von C=S entspricht. Es wurde ein Mechanismus postuliert und die kinetischen Parameter des Elektrodenprozesses wurden bestimmt.相似文献