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31.
This review summarizes the results of molecular-level studies on the mechanism of Pd/C catalyst formation from the PdCl2 precursor. Two processes occur in acidic media during the contact of H2PdCl4 with carbon: (a) adsorption of palladium chloride to form surface complexes and (b) redox interaction between PdCl2 and carbon with the formation of palladium metal particles. The ratio between these adsorbed palladium species depends on
the conditions of adsorption and especially on the size of carbon support grains and the oxidative atmosphere. The observations
are explained by the fact that carbon support exhibits electrochemical and ligand properties. X-ray diffraction, X-ray scattering,
XPS, and high-resolution electron microscopy revealed that the nanostructure of carbon materials, in particular the extent
of their three-dimensional ordering, is crucial for the ligand properties. The presence of two forms, metallic and ionic,
of sorbed palladium determines the bimodal size distribution of the metal. After the reduction of ionic species, metal particles
are “blocked” with support. The nature of the ionic forms of palladium (mostly (PdCl2)n) clusters chemically and epitaxially bound to the carbon surface suggests the mechanisms of the bimodal distribution of the
supported metal particles on the surface and the methods for the control of the ratio between “blocked,” low-dispersed, and
highly-dispersed particles in the catalyst. One of these methods is the use of palladium polynuclear hydroxo complexes (PHCs)
with low oxidation potentials as starting compounds for catalysts preparation. The data on the PHC structure in a solution
and its change upon the adsorption of PHC on the surface of the carbon material obtained by the17O,23Na,133Cs, and35Cl NMR techniques are discussed. PHCs are shown to be a clew of the [Pd(OH)2]n polymeric filament, whose fractions are bound with alkali metal ions. When PHC is adsorbed on the surface of the carbon support
and then dried, palladium oxide is formed from which highly dispersed metal particles are formed during reduction. The nature
of alkali metal ions in PHC affects the activity of the Pd/C catalyst. An important role of the ligand, electrochemical, and
lyophilic properties of carbon material during the formation of the species of the active catalyst component is discussed. 相似文献
32.
33.
B.B. Troitskii V.A. Dozorov F.F. Minchuk L.S. Troitskaya 《European Polymer Journal》1975,11(3):277-281
The dehydrochlorination of PVC under vacuum (~ 10?4 mm Hg), with continuous removal of volatile products by freezing out, has been studied at 180–250°. The equation has been deduced and solved to describe the thermal degradation of PVC. The rate constants of separate steps of polymer dehydrochlorination and the dependence of concentrations of polyenes on time of degradation are calculated. 相似文献
34.
Condensation of aromatic (heteroaromatic) aldehydes with 1,3-dicarbonyl compounds under the 1-butyl-3-methylimidazolium tetrafluoroborate
([Bmim][BF4]) ionic liquid-piperidinium acetate catalytic system (0.2 equiv. of each component) in the absence of a solvent affords,
depending on the structures of the reagents, 2-arylidene derivatives of methyl acetoacetate and acetylacetone, diethyl 2,4-bis(trifluoroacetyl)-3-phenylpentanedioate,
or dimethyl 2-aryl-4-hydroxy-6-oxocyclohexane-1,3-dicarboxylates. The reactions of the resulting 2-arylidene derivatives with
O-methylisourea in the [Bmim][BF4] ionic liquid produced methyl 2-methoxy-4-methyl-6-aryldihydropyrimidine-5-carboxylates and 1-(2-methoxy-4-methyl-6-phenyldihydropyrimidin-5-yl)ethanone
(mixtures of 3,6- and 1,6-dihydro isomers), which were transformed into the corresponding 3,4-dihydropyrimidin-2(1H)-one derivatives.
Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1199–1204, May, 2005. 相似文献
35.
Troitskii B. B. Domrachev G. A. Semchikov Yu. D. Khokhlova L. V. Anikina L. I. Denisova V. N. Novikova M. A. Marsenova Yu. A. Yashchuk L. M. 《Russian Journal of General Chemistry》2002,72(8):1276-1281
Fullerene-C60 inhibits thermal and thermooxidative degradation of copolymers of methyl methacrylate with styrene, butyl acrylate, glycidyl methacrylate, and hydroxyethyl methacrylate. 相似文献
36.
M. N. Rodnikova V. M. Troitskii D. B. Kayumova I. A. Solonina M. A. Gunina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(12):2190-2192
The isothermal compressibility and bulk viscosity of solutions of tetrahydrofuran (THF) in ethylene glycol were measured on
a unique Micro PVT Systems unit over the concentration and pressure ranges 0–20 mol % THF and 0.1–160 MPa, respectively, at
298 K. The results were interpreted from the point of view of structural changes in the ethylene glycol-THF system. 相似文献
37.
V. M. Troitskii M. N. Rodnikova T. M. Val’kovskaya M. A. Solonina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(8):1419-1420
The bulk viscosity of solutions of tetramethylurea in ethylene glycol over the concentration and pressure ranges 0–10 mol % and 0.1–300 MPa, respectively, was measured on a MicroPVT System setup. The results are interpreted in terms of structural changes in the system and solvophobic effects in solutions of the nonelectrolyte. 相似文献
38.
Investigations were made on the effects of zinc and calcium carboxylates, polyols and other oxygen-containing compounds, nitrogen- and sulphur-containing compounds and of mixtures of zinc calcium carboxylates, zinc carboxylates-complexing agent, calcium carboxylate-complexing agent and of zinc carboxylate-calcium carboxylate-complexing agent upon the rate of dehydrochlorination and crosslinking and on the absorption spectrum of PVC during degradation in vacuum at 180°. The interaction of the stabilizers with 2-chlorobutane (a model for normal units of PVC) was studied at 180°. It was shown that, in the thermal degradation of PVC, zinc carboxylates give synergistic mixtures with compounds having -OH, -SH or -NH groups. In the thermal degradation of PVC in the presence of mixtures of zinc carboxylates with polyols, there are exchanges between chloro-containing groups of PVC and carboxylic groups of salt and alcohol residue. Zinc salts also catalyze the interaction of polyols with double (particularly conjugated double) bonds of degraded PVC. The investigated compounds do not form synergistic mixtures with calcium carboxylates. The triple mixtures of zinc and calcium carboxylates with complexing agents are more effective stabilizers of PVC than the binary mixtures zinc carboxylate-calcium carboxylate and zinc carboxylate-complexing agent. The mechanism of synergistic interaction in PVC stabilization by these mixtures are discussed. 相似文献
39.
The absorption of light by polyethylene film subjected to extension and electron bombardment has been investigated on the wavelength interval 220–800 nm. It is shown that irradiation and illumination by a xenon lamp during extension reduce the stresses corresponding to the beginning of high-elastic deformation of the polyethylene. It is established that deformation and electron bombardment lead to an increase in the light absorption of the polyethylene film with absorption maxima at 245 and 290 nm. It is assumed that the nature of the effect is associated with reorientation of the macromolecule chains under the influence of mechanical stress and the appearance of allyl radicals-CH2-CH CH-H-CH2-.Institute of Physical Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 451–455, May–June, 1972. 相似文献
40.