State of Atoms and Interatomic Interactions in Complex Perovskite-Like Oxides: XVIII. Magnetic Dilution in the LaCrO<Subscript>3</Subscript>-LaGaO<Subscript>3</Subscript> System

Magnetic susceptibility of dilute solid solutions of lanthanum chromate in lanthanum gallate was studied. The calculated antiferromagnetic exchange parameter and distribution of chromium atoms over the diamagnetic matrix gave evidence for enhanced chromium aggregation and weakened magnetic exchange in lanthanum gallate compared to lanthanum aluminate.     

Sufficient conditions for asymptotic normality of sums of values of discrete random fields,dependent in strips

Sufficient conditions are given for the asymptotic normality of a sum of values of a field on a square of the integer lattice in R² with the side n for normalization by the quantity (2n+1)^3/2. Moreover, the values of the field are dependent on strips of fixed width. The method of moments is used for proof.Translated from Matematicheskie Zametki, Vol. 23, No. 5, pp. 725–732, May, 1978.     

Contribution of dimensional factor to the potential of copper-containing electron-ion exchangers

The average size of copper particles in copper-containing electron-ion exchangers is determined with the aid of microscopy and x-ray diffractometry. The results are used to calculate the contribution made by a dimensional factor to the electrode potential. Compared to the potential of compact copper, the potential shift in the negative direction measured experimentally falls within the region of calculated values. The average size of copper particles remains practically unchanged after contact with a copper sulfate solution, testifying to stabilization of an ultradisperse state of copper particles by a polymer matrix.     

Recrystallization in metal-ion exchanger nanocomposites

The rate of growth of metal (silver, copper) particles obtained by multiple chemical precipitation into sulfostyrenedivinylbenzene ion exchange matrix was studied in solutions of their own potential-determining metal ions by no-current chronopotentiometry. The potential shift of metal particles on a carrier from the potential of a compact electrode was caused by the disperse state of particles, and potential changes with time, by their growth during recrystallization. An increase in the size of silver particles with time during the initial period of the process was described by the parabolic law. Thanks to stabilization by macroporous ion exchange matrix, the growth of metal particles was substantially decelerated even under formed electron conducting cluster conditions.     

Electrochemical Peculiarities of Mediator-Assisted Bioelectrocatalytic Oxidation of Glucose by a New Type of Bioelectrocatalyst

Russian Journal of Electrochemistry - A protein extract of microbe cells is studied as a bioelectrocatalyst for glucose oxidation. The microbial protein extract prepared from Escherichia coli BB,...     

Alkyne hydrogenation using Pd–Ag hybrid nanocatalysts in surface‐immobilized dendrimers

A series of Pd–Ag mixed‐metal nanocatalysts were prepared by reduction of Pd–Ag salts in the presence of poly(propylene imine) dendrimers, which were covalently bound to the surface of a silica polyamine composite, BP‐1 (polyallylamine covalently bound to a silanized amorphous silica gel). Three different Pd‐to‐Ag ratios were evaluated (50:50, catalyst 1 ; 40:60, catalyst 2 ; 60:40, catalyst 3 ) with the goal of determining how the amount of Ag effects selectivity, rate and conversion in the selective reduction of alkynes, such as phenylacetylene and 1‐ or 4‐octyne, to the corresponding alkenes. Conditions for the catalysis are reported where there is improved selectivity without a serious reduction in rate when compared with the analogous Pd‐only catalysts. Catalyst 2 worked best for phenylacetylene and catalyst 3 worked best for the octynes. The catalysts could be reused seven times without loss of activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficiency of Pyrrole Electropolymerization under Various Conditions

The electrooxidative polymerization of pyrrole on the surface of a glassy carbon electrode was studied, while varying the solvent, the type and concentration of supporting electrolyte, redox mediator addition to the polymerization medium, and hydrodynamic conditions. The efficiency of polymerization was determined as the ratio of the charge of the redox response of the polymer film under the standard conditions to the total charge of film formation in the monomer solution. The above factors were varied to determine the conditions that allow minimization of the ratio in order to obtain the highest yield of the polymer product. This was achieved by using a combination of a redox mediator addition with active stirring of solution.

     

Electroactive Composite Pd–Polypyrrole and Its Catalytic Properties in the Reaction of Styryl Bromide Cyanation

A composite material in the form of powder is synthesized by a redox reaction in mixed aqueous solution of Pd(NH₃)₄Cl₂ + pyrrole. The composite consists of polypyrrole globules with palladium nanoparticles uniformly distributed inside the latter. Being applied as a film on the electrode surface, both components of this material exhibit redox activity. Palladium particles inside the composite exhibit catalytic properties in cyanation of styryl bromides, a reaction widely used in fine organic synthesis.     

Crystal structure of β′-Zn2V2O7

The crystal structure of the high-temperature modification of zinc pyrovanadate, namely, β′-Zn₂V₂O₇, is refined by the full-profile Rietveld method (GSAS) using the high-temperature X-ray diffraction data. The crystals are monoclinic (space group C2/m, Z = 2); the unit cell parameters are as follows: a = 6.9324(2) Å, b = 8.4394(2) Å, c = 5.0326(1) Å, and β = 108.272(2)°. Comparative analysis of the crystal structures of β′-Zn₂V₂O₇, β-Mn₂V₂O₇, and Cd₂V₂O₇ is performed.     

Stability of Ultradisperse Copper in a Sulfo Cation Exchanger Matrix

The recrystallization of ultradisperse copper chemically deposited onto a sulfo cation exchanger matrix was studied by the potentiometric method. The stationary value of the electrode potential of the copper-sulfo cation exchanger composite was established during a long period of time, which depended on the ionic form of the composite (H⁺, Cu²⁺, or Na⁺), solution composition (CuSO₄, H₂SO₄, and Na₂SO₄), and solution concentration. Recrystallization was favored by copper(II) counterions, which entered the composite as a result of ion exchange, nonexchange absorption of copper sulfate, or preliminary composite transformation into the Cu²⁺ form. In the quasi-equilibrium state, the concentration of copper(II) counterions was maintained at a high level by the Donnan interfacial potential. At all the copper(II) sulfate concentrations used, the potential of the Cu²⁺/Cu ion—metal pair in the ion-exchange matrix remained at virtually the same level, which was indicative of the stable state of copper particles. In the absence of an external source of copper ions, recrystallization was significantly hindered; therefore, the potential exhibited only a slight drift. Copper ions formed in the solution of small crystals were localized in the vicinity of ionogenic matrix centers, which decreased the mobility of these particles as counterions; therefore, the dispersity of particles remained unchanged.