Synthesis of platinum complexes containing (+)-bornyl- and (−)-menthylammonium in the outer coordination sphere and their catalytic activity in hydrosilylation reactions

Optically active (+)-bornyl- and (−)-menthylammonium platinates were synthesized starting from H₂[PtCl₆] · 4H₂O and hydrochlorides of the corresponding amines. Catalytic activity of the complexes in the hydrosilylation reactions of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 1,1,3,3-tetramethyldisiloxane and acetophenone with diphenylsilane was studied. The addition of the siloxanes leads to a predominant formation of β-adduct. Activity of the catalysts, evaluated on the 50% conversion of the substrate, decreases in the following sequence: (−)-(menthylNH₃)₂[PtCl₆] > (Et₃NH)₂[PtCl₆] > (+)-(bornylNH₃)₂[PtCl₄] > (+)-(bornylNH₃)₂[PtCl₆]. Asymmetric induction is observed in the hydrosilylation of aceto-phenone in the presence of (+)-(bornylNH₃)₂[PtCl _n ] (n = 4, 6); (+)-(bornylNH₃)₂[PtCl₆] showed the highest catalytic activity and selectivity. The hydrosilylation of acetophenone gave 1-phenylethoxy(diphenyl)silane, 1-phenylvinyloxy(diphenyl)silane, and 2-phenylethyl-2-diphenylsiloxy(diphenyl)silane as the products. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 341–349, February, 2008.     

Study on the Solvent Extraction with Radio-Tracers. I. Extraction Study on Protactinium-233 with the Noyltrifluoroacetone

Protactinium-233, separated from the irradiated thorium, was used as a tracer for the extraction study with thenoyItrifluoroacetone. From the results obtained by the variation of acidities of HCl with the constant concentration of TTA in benzene, a slope of ?2 was obtained by plotting the distribution coefficients against acidities. With a definite acid concentration of HCl in the aquous solution and by the variation of TTA concentration, a slope of 4 was obtained by plotting the distribution coefficients against the concentration of β-diketone. With these results, species extracted by the organic layer was assumed to be Pa[TTA]₂[HTTA]₂. If the composition of the organic layer was changed by the addition of the following solvents into the TTA in benzene solution, the order of the extraction was found as follows: n-amyl alcohol > cyclohexane > chloroform > n-hexane > carbon tetrachloride > benzene > nitrobenzene > hexone > cyclohexanone > n-butyl alcohol.     

Pulsed electrodeposition of Pt nanoclusters on carbon nanotubes modified carbon materials using diffusion restricting viscous electrolytes

A simple method for achieving high dispersion and small platinum nanoparticles down to only 2 or 3 nm on structured carbon supports (carbon nanotubes-modified PAN-based carbon fiber and carbon nanotubes-modified graphite foil) is presented. Pulsed electrodeposition of Pt nanoparticles was performed at increased viscosity of the H₂PtCl₆ containing electrolyte by addition of glycerol. The catalyst nanoparticle size can be controlled by varying the amount of glycerol added into the aqueous H₂PtCl₆ solution, and adjusting the number of the potential pulses. The shape and size of the Pt nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic properties of Pt nanoparticles with respect to O₂ and H₂O reduction were investigated by means of cyclic voltammetry, and the improved catalytic activity of the Pt nanoparticles/carbon nanotubes surfaces could be proved.     

Dielectric Barrier Discharge Initiated Gas-Phase Decomposition of CO2 to CO and C6–C9 Alkanes to C1–C3 Hydrocarbons on Glass, Molecular Sieve 10X and TiO2/ZnO Surfaces

Atmospheric Pressure Dielectric Barrier Discharge (APDBD) initiated decomposition of CO₂ and C₆–C₉ alkanes (in Ar carrier) with uncoated and TiO₂/ZnO coated glass surfaces, and under molecular sieve 10 X packing are presented in this study. Alkanes employed include 2-methylpentane, cyclohexane, n-hexane, n-heptane, n-octane, n-nonane and their decomposition products studied include C₁–C₃ hydrocarbons viz. CH₄, C₂H₄, C₂H₆ and C₃H₈. Generally the yields of all these C₁–C₃ products increased with discharge energy, however to a major extent the parent alkane structure controlled the relative concentration profiles of the individual products. Typically the slopes of the increase in various products yield varied from 0.025 to 0.25 ppm (v/v) mm V⁻¹. However, in the case of cyclohexane the total yield of methane, ethane and propane were only ∼20% of ethylene yield. Use of TiO₂ as well as TiO₂/ZnO coated central glass electrode in the APDBD apparatus showed ∼11% enhancement in degradation efficiency. However, while overall 2-methylpentane decomposition reduced significantly to ∼30%, in case of n-octane its decomposition to the C₁–C₃ products remained unaffected. On the other hand under molecular sieve 10X packing, yield of CH₄ and C₂H₄ increased significantly in both cases.     

Enthalpies of solution of <Emphasis Type="Italic">n</Emphasis>-alkanes in mixtures of MeCN with alkan-1-ols at 298.15 K. Relations between the thermodynamic properties of binary and ternary systems

The solution enthalpies of n-hexane, n-nonane, and n-undecane in mixtures of MeCN with EtOH, PrOH, and BuOH were determined by calorimetric method at 298.15 K. Relations between the thermodynamic properties of ternary systems and the properties of the binary solvents and the solute are discussed. To predict the enthalpies of solution of hydrocarbons in mixed solvents whose components have strongly different molar volumes (V ₂/V ₁ > 1.5), it is proposed to use the values that are additive in the volume fraction scale. The solution enthalpies of hydrocarbons in mixtures characterized by close molar volumes of the components strongly depend on the excess properties of the binary solvent.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1578–1582, August, 2004.     

Evaluation of the Thermodynamic Parameters for the Adsorption of Some Hydrocarbons on Chemically Treated-Bentonites by Inverse Gas Chromatography

Inverse gas chromatography has been used to evaluate the adsorption parameters (ΔH_a, ΔH_st, ΔS_a and ΔG_a) of some probe molecules, each representing a class of organic (n-hexane, cyclohexane, benzene, n-octane, 1-octene and isooctane) on bentonite and chemically treated-bentonites. The adsorption parameters of the probes on the bentonite samples were determined in infinite dilution region. Adsorption of the organic species was investigated in the temperature range of 200–275^∘C, using a flame ionization detector, and nitrogen as a carrier gas. The net retention volumes (V_n) of the probes were determined by the help of the retention times (t_R) observed on gas chromatograms for each probe. Injection was made at least three times for each probe, obtaining reproducible results of ± 0.5%. It was found that benzene exhibits more negative ΔH than for n-hexane and cyclohexane on all of the adsorbents. In addition, it was found that 1-octene exhibits more negative ΔH than for n-octane and isooctane on the chemically treated-bentonites, whereas n-octane exhibits more negative ΔH than for 1-octene and isooctane on the natural bentonite. Also, interactions of benzene with the natural- and chemically treated-bentonites were found to be stronger than those of n-hexane and cyclohexane with the same carbon number. Again, interactions of the 1-octene with the chemically treated-bentonites were found to be stronger those of n-octane and isooctane with the same carbon number. On the contrary, interactions of n-octane with the untreated-bentonite were found to be stronger than those of 1-octene and isooctane.     

Transformations of cyclohexane and benzene on the bimetallic Ru-Pt oxide catalysts

The bimetallic Ru-Pt/Al₂O₃ catalysts with an overall metal content of 1 wt. % and Pt: Ru weight ratios from 1: 3 to 3: 1 were studied. The catalytic activity for cyclohexane and benzene transformations, including hydrogenation, hydrogenolysis, and skeletal isomerization of the initial substrates and products of intermediate transformations, was studied at temperatures 180–350 °C and H₂ pressures from 1.0 to 5.0 MPa. The maximum yield of n-hexane from cyclohexane and benzene was obtained on the catalysts with a ruthenium content of 0.75–1.0%, being ∼29–30 wt.% at 40% selectivity. The selectivity to form n-hexane decreases with an increase in the cyclohexane conversion and is almost independent of the composition of the Ru-Pt system. On the catalysts under study, benzene is converted to the same products but at temperatures by 60 °C lower as compared to cyclohexane conversion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 633–637, April, 2006.     

Evaluation of Excess Gibbs Energy of Mixing in Binary Mixtures of Di-Isobutyl Ketone (Dibk) and Nonpolar Solvents

Abstract

Excess Gibbs energy of mixing in binary mixture of Di-isobutyl ketone (DIBK) in nonpolar solvents namely n-heptane, p-xylene, cyclohexane, dioxane, benzene and tetra-chloromethane have been evaluated at 303°K. The results indicate that (ΔG_AB)_maxima is in the order, n-heptane > p-xylene > cyclohexane > benzene > dioxane > tetra-chloromethane.     

Catalytic Performance of Re/Ga2O3/WO3/ZrO2 Catalyst for n-Hexane Isomerization

A series of Re/Ga₂O₃/WO₃/ZrO₂ catalysts were prepared by the impregnation method. The crystalline structure, redox, and acid site distribution of the catalysts were characterized by X-ray powder diffraction, temperature-programmed reduction of H₂, and temperature-programmed desorption of NH₃. Their catalytic performance for n-hexane isomerization was studied. The results showed that the addition of Re greatly affected the redox properties and the acid site distribution of the catalysts. Owing to the presence of Re, n-hexane isomerization was catalyzed by metal and acid sites, and thus the conversion of n-hexane and the selectivity for 2,2-dimethylbutane were significantly increased. Under the conditions of 195 °C, 1.0 MPa, LHSV = 1.0 h⁻¹, and n(H₂)/n(C₆) = 2.0, the conversion of n-hexane over 1.0%Re/1.0%Ga₂O₃/WO₃/ZrO₂ is 84.8%, and the selectivities for 2,2-dimethylbutane, i-hexane, and cracking products (C_5-) are 20%, 97.7%, and 2.1%, respectively. The catalyst is stable during 150 h operation.     

Cost-effective electrodeposition of platinum nanoparticles with ionic liquid droplet confined onto electrode surface as micro-media

We report here for the first time on the use of a droplet of water-immiscible ionic liquid (IL) containing metallic precursor confined onto electrode surface as new micro-media for cost-effective electrodeposition of platinum nanoparticles. 1-n-Butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆), a typical water-immiscible IL, is found to be able to form a stable droplet onto electrode surface in which the metallic precursor (i.e., chloroplatinic acid hexahydrate (H₂PtCl₆)) for electrodeposition of Pt nanoparticles can be stably dissolved when the prepared electrode is used in aqueous solutions. The electrodeposition of Pt nanoparticles is carried out in the aqueous solution of 0.1 M KPF₆ with the H₂PtCl₆-containing IL droplet-confined glassy carbon electrode as working electrode at −1.5 V vs. Ag/AgCl. The Pt nanoparticles electrodeposited from the IL droplet micro-medium are characterized to have a uniform morphology and to possess an excellent electrocatalytic activity toward the oxidation of methanol. Compared with the existing methods for the electrodeposition of metals with ILs as the solvents, the method demonstrated here requires a less amount of ILs and metallic precursors and is thus anticipated to provide a new and cost-effective approach to the deposition of metallic nanoparticles onto conducting substrate.     

Reactions ofn-hexane andn-nonane on Pt catalysts and hydrogenating off hydrocarbonaceous adspecies after reaction

n-Hexane andn-nonane were reacted on Pt black, 6% Pt/SiO₂, 0.8% Pt/KL zeolite and a 0.6% industrial Pt/Al₂O₃ catalyst. Selectivities were compared at ∼10% conversion. After reaction, the catalyst was exposed to H₂ and the hydrocarbons leaving the catalysts were analyzed. The amount of hydrocarbons left the catalysts decreased in the sequence Pt black>Pt/SiO₂>Pt/KL>Pt/Al₂O₃. The composition of removed hydrocarbons gave important—although indirect—information on the possible state of “hydrocarbonaceous deposits” during catalysis.     

Synthesis of Barium Sulfate Nanoparticles in Water-in-Oil Microemulsion Systems

Micellar solutions of poly(ethylene glycol) octylphenyl ether and n-hexyl alcohol in cyclohexane were used to study the formation of water-in-oil microemulsion system and to synthesize barium sulfate nanoparticles. Barium sulfate particles (the average diameter is 10 nm) were obtained by mixing two microemulsion systems containing Ba²⁺and SO^2– ₄ions. It was shown that the sizes of BaSO₄particles measured by the dynamic light scattering and electron microscopy are in good agreement with each other.     

Liquid Solution Densities of Ternary-Pseudobinary Mixtures of (Benzene + Cyclohexane) in the Presence of Tetrachloromethane or <Emphasis Type="Italic">n</Emphasis>-Hexane

Densities have been obtained as a function of composition for ternary-pseudobinary mixtures of [(benzene + tetrachloromethane or n-hexane) + (cyclohexane + tetrachloromethane or n-hexane)] at atmospheric pressure and the temperature 298.15 K, by means of a vibrating-tube densimeter. Excess molar volumes, V_m^E, partial molar volumes and excess partial molar volumes were calculated from the density data. The values of V_m^E have been correlated using the Redlich–Kister equation and the coefficients and standard errors were estimated. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, CCl₄ or n-C₆H₁₄, have quite different influences on the volumetric properties of binary liquid mixtures of benzene with cyclohexane.     

Solvent effect on the synthesis of monodisperse amine-capped Au nanoparticles

A remarkable solvent effect in a single-phase synthesis of monodisperse amine-capped Au nanoparticles is demonstrated.Oleylamine-capped Au nanoparticles were prepared via the reduction of HAuCU by an amine-borane complex in the presence of oleylamine in an organic solvent.When linear or planar hydrocarbon(e.g.,n-hexane,n-octane,1-octadecylene,benzene,and toluene) was used as the solvent, high-quality monodisperse Au nanoparticles with tunable sizes were obtained.However,Au nanoparticles with poor size dispersity were obtained when tetralin,chloroform or cyclohexane was used as the solvent.The revealed solvent effect allows the controlled synthesis of monodisperse Au nanoparticles with tunable size of 3-10 nm.     

Formation of polyaniline/Pt nanoparticle composite films and their electrocatalytic properties

Polyaniline (PANI) thin films modified with platinum nanoparticles have been prepared by several methods, characterised and assessed in terms of electrocatalytic properties. These composite materials have been prepared by the in situ reduction of a platinum salt (K₂PtCl₄) by PANI, in a variety of solvents, resulting in the formation of platinum nanoparticles and clusters of different sizes. The further deposition of platinum clusters at spin cast thin films of PANI/Pt composites from a neutral aqueous solution of K₂PtCl₄ has also been demonstrated. Thin-film electrodes prepared from these materials have been investigated for their electrocatalytic activity by studying hydrazine oxidation and dichromate reduction. The properties of the composite materials have been determined using UV–visible spectroscopy, atomic force microscopy and transmission electron microscopy. The nature of the material formed is strongly dependent on the solvent used to dissolve PANI, the method of preparation of the PANI/Pt solution and the composition of the spin cast thin film before subsequent deposition of platinum from the aqueous solution of K₂PtCl₄.Dedicated to Professor Dr. Alan Bond on the occasion of his 60th birthday.     

甲醇重整反应中Pt/γ-Al2O3催化剂纳米Pt粒径与催化性能关系研究

利用硝基甲烷还原法在室温条件下得到了纳米Pt粒径可控的担载Pt/γ-Al₂O₃催化剂, 并利用甲醇重整反应为反应探针考察了Pt粒径与催化反应性能之间的关系, 发现催化反应的性能与担载贵金属颗粒粒径之间存在明显的相关性. 通过透射电镜(TEM)、X射线衍射(XRD)、程序升温还原(TPR)等测试手段对催化剂进行表征, 发现钠米Pt的粒径大小不但影响甲醇重整反应的活性, 同时也影响反应的选择性, 即催化剂的催化性能与担载贵金属粒径之间存在明显的尺度效应.     

Divalent transition metal complexes of 3,5-pyrazoledicarboxylate

New divalent transition metal 3,5-pyrazoledicarboxylate hydrates of empirical formula Mpz(COO)₂(H₂O)₂, where M=Mn, Co, Ni, Cu, Zn and Cd (pz(COO)₂=3,5-pyrazoledicarboxylate), metal hydrazine complexes of the type Mpz(COO)₂N₂H₄ where M=Co, Zn or Cd and Mpz(COO)₂nN₂H₄·H₂O, where n=1 for M=Ni and n=0.5 for M=Cu have been prepared and characterized by physico-chemical methods. Electronic spectroscopic data suggest that Co and Ni complexes adopt an octahedral geometry. The IR spectra confirm the presence of unidentate carboxylate anion (Δν=ν_asy(COO^–)–ν_sym(COO^–)>215 cm^–1) in all the complexes and bidentate bridging hydrazine (ν_N–N=985–950 cm^–1) in the metal hydrazine complexes. Both metal carboxylate and metal hydrazine carboxylate complexes undergo endothermic dehydration and/or dehydrazination followed by exothermic decomposition of organic moiety to give the respective metal oxides as the end products except manganese pyrazoledicarboxylate hydrate, which leaves manganese carbonate. X-ray powder diffraction patterns reveal that the metal carboxylate hydrates are isomorphous as are those of metal hydrazine complexes of cobalt, zinc and cadmium.     

Dependence of the catalytic activity of Ag/Al2O3 on the silver concentration in the selective reduction of NOx with n-hexane in the presence of H2

The activity of 0.25–5% Ag/Al₂O₃ catalysts in the selective catalytic reduction of nitrogen oxides with n-hexane under the conditions of promotion with a small amount of H₂ was studied. It was found that, upon the introduction of ∼1000 ppm of H₂ into the reaction mixture, the Ag/Al₂O₃ samples containing 1–2% Ag exhibited optimum activity and selectivity. It was established that, in the presence of 1000 ppm of H₂, the rate of the selective catalytic reduction of NO _x was higher by a factor of 10–13, and the onset temperature of the reaction was lower by approximately 100°C. It was found by X-ray photoelectron spectroscopy, temperature-programmed reduction, and UV spectroscopy that the high activity of 1–2% Ag/Al₂O₃ catalysts was due to the presence of small Ag _n ^δ+ and Ag _m ⁰ clusters on their surface. A decrease in the concentration of Ag below the optimum value resulted in the predominance of an inactive ionic form on the catalyst surfaces. As the concentration of Ag was increased (>2%), large particles of Ag₂O and Ag⁰, which facilitate the oxidation of n-C₆H₁₄, were formed to lead to a decrease in selectivity and in the degree of reduction of nitrogen oxides.     

Effect of chelation on the polycondensation of monomers having an active ester group

Various amino acid esters and dicarboxylic acid esters having a β-thioether group have been synthesized and their polycondensation with diamine was found to occur at room temperature to form polyamide thioether. The effect of solvents or chelating agents on their polycondensation reaction was investigated. Metal acetylacetonates or inorganic salts had a great influence on the rate of the polycondensation reaction, and the catalytic activity of metal acetylacetonates M(AcAc)_n or inorganic salts decreased in the following order: Mg(AcAc)₂?Th(AcAc)₄>Cu(AcAc)₂>Li(AcAc)>None>Zr(AcAc)₄, MgCl₂·6H₂O>CuCl₂·.2H₂O>ZnCl₂>MgCl₂>None. It was also found that the amount of polyamide thioether was dependent on solvents or the presence of chelating agents because the polycondensation rate and the apparent equilibrium between ring and chain structures were both greatly influenced by solvents or chelating agents. These effects of solvents or chelating agent on the polycondensation may be attributable to formation of a complex with the thioether group which enhances the reactivity of ester.     

Synthesis of nickel metal nanoparticles via a chemical reduction of nickel ammine and alkylamine complexes by hydrazine

Nickel nanoparticles were prepared from their coordination compounds, such as [Ni(NH₃)₆]Cl₂, [Ni(N₂H₄)₂Cl₂], [Ni(HNEt₂)₆]Cl₂, and [Ni(H₂NBu)₆]Cl₂ in aqueous solution by chemical reduction. The reaction of nickel ammine and alkylamine complexes with hydrazine monohydrate as a reducing agent was carried out at 90 °C and pH = 10–12. Depending on the influencing parameters such as oxidizing agent, pH, and temperature, the hydrazine reaction can be carried out in different pathways. The chemical reduction method is a simple procedure and also is the best one in the controlling of composition, size, and shape of Ni powder. The reduction of nickel complexes into the metallic Ni powder occurs via the dissociation of complexes and reduction by hydrazine in alkaline solution. Therefore, complexing agents have the most effect on the reduction reaction. The results show that, when the ligands in complexes were changed from ammine to diethylamine and butylamine, respectively, the crystalline size and morphology of nickel metal nanoparticles are changed. The chemical reduction of nickel complexes into metallic nickel can be accompanied with a change in the crystalline system. The pure nickel crystalline has a face-centered cubic structure. The nickel nanoparticles were characterized using IR spectroscopy, X-ray powder diffraction, scanning electron microscopy and vibrating sample magnetometer analyses.