Polymerization of isoprene on a modified “neodymium” catalytic system

Polymerization of isoprene using the catalytic system NdCl₃·3i-C₃H₇OH-Al(i-C₄H₉)₃ modified with methylalumoxane was studied. The kinetic parameters of the process and the molecular characteristics of the polyisoprene obtained were determined.     

Synthesis of some new germasesquioxides by intramolecular catalytic Mannich-type reactions

A convenient procedure for the preparation of some new germasesquioxides containing phosphonyl groups carried by an intramolecular catalytic Mannich-type reaction is reported.     

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni²⁺/Cr³⁺ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni²⁺/Cr³⁺ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ～400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 Å. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 Å). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 Å is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni⁰ crystallites with a size of ～5.5 nm and a specific surface area of ～7.0 m² g^?1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO₂. The catalysts with the ratio Ni²⁺/Cr³⁺ = 1/(2?3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.     

Studies on the Electrochemical Reduction of Cyanocobinamide

l.INTR0DUCTIONVitaIninBlz(cyanocobalamin)anditScoenZymesasmostdrip0rtanmoleculeshavebeenextensivelystUdied.However,themetabolicreacti0nsofvitaIninBl2throughWhichtheintuellarconversi0ntoitSc0empeformsinmanunaliancellsarelargelyunkn0wnanduncharacterized[l].SeverallinesofevidencesuggestedthatvitaIninBl2mustbereducedpri0rtoformingitsc0e~es[2].Thus,theconversionofvitaIninBl2toitSc0enZyIneformsincellsneedsreductionreagents,suchasFMNapdNADHwithreducedglutathione[l].lnaddition,itwasreP0r…     

The cooperative effect of a hydroxyl and carboxyl group on the catalytic ability of novel β-homoproline derivatives on direct asymmetric aldol reactions

Novel β-homoproline derivatives, 2-hydroxy-2-(pyrrolidin-2-yl)acetic acids (R,S)- and (S,S)-1a-d, were synthesized. All of the prepared compounds were used as organocatalysts in the direct asymmetric aldol reaction of 4-nitrobenzaldehyde with several ketones. Among these catalysts, (R)-2-hydroxy-2-((S)-pyrrolidin-2-yl)acetic acid (R,S)-1a showed good catalytic ability in the formation of aldol product 13 (up to 69% ee, 95% yield), which was similar to the results catalyzed by l-proline (71% ee, 96% yield). Relatively low yields and low enantioselectivities were observed in aldol reactions catalyzed by (S,S)-1a, for example, 13 was obtained in 55% yield and 13% ee. The aldol reaction catalyzed by the methyl-protected carboxylic acid 1b and esters 1c,d produced much lower chemical yields and enantioselectivities during the formation of 13. The cooperative effect of the (R)-configured hydroxyl group and the carboxyl group was found to play an important role in inducing enantioselectivity in the aldol reaction. Relatively high diastereoselectivities (anti:syn = 85:15) and enantioselectivity (anti, 83% ee) were observed in the aldol reactions of 4-nitrobenzaldehyde with cyclohexanone, which was catalyzed by (R,S)-1a.     

Heterogeneous reactions of sulfur dioxide on dust

In urban atmospheric environment, SO2 is the prin- cipal sulfur-containing anthropogenic pollutant, with concentrations reaching into hundreds of parts per bil- lion[1]. Atmospheric SO2 can be adsorbed and oxidized to sulfate on the surface of particles and subsequently involved in the formation of secondary inorganic aerosol in the atmosphere[2―4]. Sulfate particles are known to affect climate by scattering solar radiation, resulting in a net cooling effect, as well as acting as cloud conde…     

Electrochemical study of the corrosion inhibition ability of “smart” coatings applied on AA2024

Smart epoxy coatings modified with different additives were applied on AA2024. The following three different systems were studied: a reference consisting of an epoxy coating containing chromate active pigments and two “smart” coatings modified with containers loaded with corrosion inhibitor—layered double hydroxides filled with mercaptobenzothiazole and tubular halloysites (HS) filled with 8-hydroxyquinoline. The thickness of the coatings was determined by scanning electron microscopy. The barrier properties and the average corrosion resistance were assessed by electrochemical impedance spectroscopy (EIS). The long-term corrosion repair ability of the various coatings was confirmed by EIS measurements carried for a period of 3 weeks in scratched samples. The ability of the smart additives to inhibit corrosion over defects with different sizes and geometry was studied at the microscale by using localized impedance spectroscopy (LEIS) and the scanning vibrating electrode technique. The results demonstrate that the additives provide effective corrosion inhibition on defects of various sizes. Moreover, the LEIS measurements give some important highlights concerning the mechanisms and kinetics of inhibition of each system.     

Construction of the reaction networks for heterogeneous catalytic reactions: Fischer—Tropsch synthesis and related reactions

The key approaches to the generation of reaction networks for the synthesis of products from CO and H₂ are considered. The selection rules for the elementary steps on the surface of heterogeneous catalysts are formulated. Data on the surface compounds and steps related to reactions of CO and H₂ are analyzed and a set of transforms (models of elementary steps) for generation of the reaction network are selected. Eight variants of generation of reaction networks for the formation of C1 products with different sets of transforms (12 to 31) were tested in computer experiments, and eight reaction networks comprising 34 substances and 132 to 1647 elementary steps were obtained. The pathways to CO₂, CH₄, and CH₃OH and pairs of compounds CH₄, CO₂ and CH₄, HCOOH obtained from the reaction network (220 elementary steps) are compared with the published schemes.     

Does phenomenological kinetics provide an adequate description of heterogeneous catalytic reactions?

Phenomenological kinetics (PK) is widely used in the study of the reaction rates in heterogeneous catalysis, and it is an important aid in reactor design. PK makes simplifying assumptions: It neglects the role of fluctuations, assumes that there is no correlation between the locations of the reactants on the surface, and considers the reacting mixture to be an ideal solution. In this article we test to what extent these assumptions damage the theory. In practice the PK rate equations are used by adjusting the rate constants to fit the results of the experiments. However, there are numerous examples where a mechanism fitted the data and was shown later to be erroneous or where two mutually exclusive mechanisms fitted well the same set of data. Because of this, we compare the PK equations to "computer experiments" that use kinetic Monte Carlo (kMC) simulations. Unlike in real experiments, in kMC the structure of the surface, the reaction mechanism, and the rate constants are known. Therefore, any discrepancy between PK and kMC must be attributed to an intrinsic failure of PK. We find that the results obtained by solving the PK equations and those obtained from kMC, while using the same rate constants and the same reactions, do not agree. Moreover, when we vary the rate constants in the PK model to fit the turnover frequencies produced by kMC, we find that the fit is not adequate and that the rate constants that give the best fit are very different from the rate constants used in kMC. The discrepancy between PK and kMC for the model of CO oxidation used here is surprising since the kMC model contains no lateral interactions that would make the coverage of the reactants spatially inhomogeneous. Nevertheless, such inhomogeneities are created by the interplay between the rate of adsorption, of desorption, and of vacancy creation by the chemical reactions.     

Study of pre-equilibrium effects on α-induced reactions on copper

A stack of natural copper was bombarded with -particles. Cumulative cross-sections for⁶⁵Ga,⁶⁶Ga and⁶⁵Zn production, and the excitation functions for⁶⁸Ga and⁶⁷Ga production, were measured using high resolution gamma-ray spectroscopy. The data are compared with the theoretical result provided by equilibrium and pre-equilibrium reaction model, for this purpose we used the code ALICE of Blann. The overall agreement with theory is good. Besides, we present the experimental data obtained by other authors.     

Influence of chemical composition of nanocrystalline iron’s surface on the rates of two parallel reactions: nitriding and catalytic decomposition of ammonia

Influence of chemical composition of nanocrystalline iron’s surface on its activity in the nitriding process of iron and catalytic decomposition of ammonia was studied. The rate of the nitriding reaction was measured by the thermogravimetric method using a tubular differential reactor. Hydrogen concentration in the reactor was also measured. The rate of the catalytic decomposition of ammonia was determined using the reactor’s mass balance. Experiments were conducted at different temperatures within the range from 300°C to 525°C. Iron catalyst for ammonia synthesis was studied. Two sorts of samples with a different content of potassium oxide (0.16 mass % and 0.64 mass % of K2O) were used. The composition of samples from the second group was modified by an addition of different amounts of sulfur. At temperatures above 400°C, when the effect of ammonia decomposition on the gas phase composition was experimentally measured, the presence of potassium and sulfur on the iron surface influenced the rate of the iron nitriding process. The ammonia decomposition rate was higher for samples with a greater amount of potassium. The rate of reactions depended also on the sulfur concentration and dropped when the sulfur content increased. The value of apparent activation energy of ammonia decomposition was in the range of 150 kJ mol⁻¹ to 180 kJ mol⁻¹ while the content of sulfur in the samples increased.     

Studies on solid state reactions of coordination compounds

A series of tetranuclear Mo(W)-Ag mixed-metal clusters have been synthesized by makinguse of the solid state reactions of[NH_4]_2[MYS_3](M=Mo,W;Y=O,S),AgX(X=Cl,Br,I)and(n-Bu)_4NX'(X'=Cl,Br),two of which[(n-Bu)_4N]_3[MoOS_3Ag_3Br_4](1)and[(n-Bu)_4N]_3[WS_4Ag_3Cl_4](2)have been structurally characterized by X-ray analysis.The crystal data:1,cubic,P 3m,a=12.093(4) ,Z=1,R=0.076;2,cubic,P 3m,a=12.059(2) ,Z=1,R=0.075.The clusteranion core[Ag_3MS_3X']of the two compounds can be viewed as a cube in which the four metal atomsand the four non-metal atoms are statistically distributed,respectively.Substitution reaction withPPh_3 ligand is also discussed for this type of tetranuclear clusters.     

Electrochemical Studies on the Deposition of Neodymium in DMSO

IntroductionTherareearthsandtheiralloysarewidelyusedasmagnetic,ophcal,nuclear,andsuperconductingmaterials.IfsuchametalthinfilInwaspreParedbyelectrodeposition,thefimctionefficiencywouldbegreatlyborovedandtheaPplicationfieldshouldex-pandextensively.However,theelectrodepositionofrareearthfromaqueoussoluhoniscomPlicatedbythefactthathydrogenisevolvedbeforerareearthisdeposited.Thus,aProhcnonaqueoussolventssuchasddriethylformandde(DMF),dAnethylsulfoxide(DMSo),propylenecarbonate(PC),andformandde…     

Study on Synthesis and Electrochemical Properties of Nanophase Li-Mo-spinel

Li-Mn-spinel was synthesized using the rheological phase recation method,First,the precursor was prepared by rheological phase reaction.The it was decomposed to form Li-Mn-spine,which was characterized by X-ray diffraction analysis and IR spectra.The particle size of Li-Mn-spinel was determined by the method of the transmission electron microscopy.The synthesized materials are of nanometer size with 30-100nm in the average diameter.The electrochemical properties of the Li-Mn-spinel were also studied.It proved that this method not only provided a simple practicable and effective route for the synthesis of Li-Mn-spinel,but also had many advantages such as lower sintering temperature,shorter sintering time,fine particles and particularly excellent electrochemical performances.     

Effect of Additive Agent on the Electrochemical Capacitance of Activated Carbon

In order to compare the effect of additive agent on the electrochemical capacitance of activated carbon, three additive agents like carbon nanotubes (CNTs), activated carbon fibre (ACF) and acetylene black (AB) were added to activated carbon by ultrasonic dispersion. Two electrodes including 95wt.% activated carbon, 2wt.% additive agent and 3wt.% PTFE binder were prepared. ECs were assembled in an argon-filled glove box by sandwiching a microporous separator (Celgard 2400) between two ele…     

“On Water” promoted N-arylation reactions using Cu (0)/myo-inositol catalytic system

Myo-inositol is originally applied as a cardiovascular medicine in clinic, which can be multi-ton manufactured via extraction from the byproducts in agricultural product processing such as defatted rice bran and corn-soaking water. Herein, the application of myo-inositol (MI) as a novel versatile tridentate O-donor ligand has been first described for promoting Cu-catalyzed amination reaction in aqueous medium.     

Electrochemical reactions of reversible intercalation in Chevrel compounds for cationic transfer – Principle and application on Co2+ ion

The process is an application of the reversible electrochemical reactions of insertion and deinsertion in the mineral host matrix M_xMo₆S₈ Chevrel phases to carry out the transfer of cations between two electrolytes. The device and the associated process are built around an electrochemical transfer junction (ETJ) placed between two tanks. The whole allows a transfer of cobalt cations (∼5 × 10⁻⁶ mol/h/cm² for a junction thickness of 4 mm) by application of a current density controlled between electrodes placed in both tanks.