Factors determining the chemoselectivity of phosphorus-modified palladium catalysts in the hydrogenation of chloronitrobenzenes

The precursor nature effect on the state of the Pd–P surface layer in palladium catalysts and on their properties in the liquid-phase hydrogenation of chloronitrobenzenes under mild conditions has been investigated. A general feature of the Pd–P-containing nanoparticles obtained from different precursors and white phosphorus at P/Pd = 0.3 (PdCl₂ precursor) and 0.7 (Pd(acac)₂ precursor) is that their surface contains palladium in phosphide form (BE(Pd3d _5/2) = 336.2 eV and BE(Р2р) = 128.9 eV) and Pd(0) clusters (BE(Pd3d_5/2) = 335.7 eV). Factors having an effect on the chemoselectivity of the palladium catalysts in chloronitrobenzenes hydrogenation are considered, including the formation of small palladium clusters responsible for hydrogenation under mild conditions.     

Synthesis,properties, and activity of nanosized palladium catalysts modified with elemental phosphorus for hydrogenation

The applicability of elemental phosphorus as a modifier of palladium catalysts for hydrogenation was demonstrated, and the conditions for the synthesis of nanoparticles that are highly efficient in hydrogenation catalysis were optimized. The modifying effect of elemental phosphorus depends on the P/Pd ratio; it is associated with changes in the catalyst dispersity and the nature of the formed nanoparticles containing various palladium phosphides (PdP₂, Pd5P₂, and Pd₆P) and Pd(0) clusters. The main stages of the formation of palladium catalysts for hydrogenation were determined, and a model of an active catalyst, in which the Pd₆P phosphide is the core of a nanoparticle and Pd(0) clusters form a shell, was proposed.     

Hydrogen dynamics in Ce2Fe17H5: inelastic and quasielastic neutron scattering studies

The vibrational spectrum of hydrogen and the parameters of H jump motion in the rhombohedral Th(2)Zn(17)-type compound Ce(2)Fe(17)H(5) have been studied by means of inelastic and quasielastic neutron scattering. It is found that hydrogen atoms occupying interstitial Ce(2)Fe(2) sites participate in the fast localized jump motion over the hexagons formed by these tetrahedral sites. The H jump rate τ(-1) of this localized motion is found to change from 3.9 × 10(9) s(-1) at T = 140 K to 4.9 × 10(11) s(-1) at T = 350 K, and the temperature dependence of τ(-1) in the range 140-350 K is well described by the Arrhenius law with the activation energy of 103±3 meV. Our results suggest that the hydrogen jump rate in Th(2)Zn(17)-type compounds strongly increases with decreasing nearest-neighbor distance between the tetrahedral sites within the hexagons. Since each such hexagon in Ce(2)Fe(17)H(5) is populated by two hydrogen atoms, the jump motions of H atoms on the same hexagon should be correlated.     

Dynamic modulus of polymethylmethacrylate saturated with carbon dioxide

The authors have devised a method for measuring the complex modulus of elasticity of non-plasticized polymethylmethacrylate of grade ST-1-110 in an atmosphere of carbon dioxide. The pressure of the saturated gas in the working chamber was varied between 4·10⁵ and 60·10⁵ N/m², and the experiments were performed at 18–90°C.S. M. Kirov Ural Polytechnic Institute, Sverdlovsk. Translated from Mekhanika Polimerov, No. 2, pp. 370–372, March–April, 1974.     

Nuclear-spin-lattice relaxation in the organic superconductor (BEDT-TTF)2Cu[N(CN)2]Br0.8Cl0.2

The behavior of the spin-lattice relaxation rate of ¹H nuclei in the organic superconductor (BEDT-TTF)₂Cu[N(CN)₂]Br_0.8Cl_0.2 in the temperature interval 12–319 K is investigated. A relaxation rate maximum, which depends on the resonance frequency and is associated with thermally activated vibrations of the end ethylene groups in the BEDT-TTF molecules, is observed in the vicinity of 270 K. The relaxation rate is observed to deviate from Korringa behavior at T<100 K. These deviations can be attributed to the existence of strong antiferromagnetic spin correlations. Fiz. Tverd. Tela (St. Petersburg) 39, 39–41 (January 1997)     

Experimental determination of superheated liquid density by the optical fiber method

An experimental approach to determination of the density of liquid superheated with respect to the liquid-vapor equilibrium temperature, including the range of high degrees of superheating, is developed. The approach is based on application of an optical fiber method combined with a pure bubble chamber. Performance of the method for investigation of the refractive index and density for superheated liquids as functions of temperature and pressure is illustrated in experiments with n-hexane as a reference substance for thermophysical measurements. The relative density measurements are performed with a resolution up to 10^?4 at a characteristic time of 1 ms. For absolute measurements, the setup should be calibrated by the known data on the liquid density for the saturation line.