Effect of Controlled Deactivation on the Properties of a Supported Nickel Catalyst in the Reactions of Liquid-Phase Hydrogenation of Carbon–Carbon Multiple Bonds

Russian Journal of General Chemistry - The effect of controlled deactivation of Ni/SiO2 catalysts in the reactions of liquid-phase reduction of the carbon–carbon double bond in maleic acid...     

Effect of the Size of Polyacrylamide-Stabilized Palladium Nanoparticles Supported on γ-Fe2O3 on Their Catalytic Properties in the Hydrogenation of Phenylacetylene

Theoretical and Experimental Chemistry - Hydrogenation catalysts derived from palladium nanoparticles varying in size supported on maghemite (γ-Fe2O3) were obtained by varying the...     

Oligomerization of α-Methylstyrene in the Presence of Mordenite Type Zeolite

The activity and selectivity of coarse-porous H-mordenite in synthesis of cyclic and linear dimers of -methylstyrene were studied.     

De‐agglomeration of Silica Nanoparticles in the Presence of Surfactants

The effect of the type of surfactant and pH on de‐agglomeration of a hydrophilic silica nano‐powder in a high shear mixer was investigated. It has been found that the presence of surfactant does not affect the general pattern of de‐agglomeration characterized by the transition of a single modal aggregates size distribution with the median of 10 µm, through a bi‐modal distributions with the second median of the order of 100 nm to a single modal distribution with the median of the order of 100 nm. None of the investigated surfactants enabled de‐agglomeration of the nano‐powder into a primary nanoparticle.

At pH=4, breakage of large secondary aggregates was enhanced by the addition of PEG and PVP, whereas the addition of SDS slowed down de‐agglomeration. The final aggregates were larger in all suspensions containing surfactant than in surfactant free suspensions. At pH=9 all surfactants drastically reduced de‐agglomeration rate without affecting the size of the primary aggregates. PEG induced bridge flocculation of the primary aggregates leading to a drastic change of the rheology of suspension.     

Reactions of Some Terpenoids with CH-Acids in the Presence of Cs-β Zeolite

Reactions of some ,-unsaturated ketones from terpenoid series with CH-acids in the presence of Cs- zeolite were studied under various conditions. The variation of reaction conditions (heating, ultrasonic irradiation) strongly affected the reaction products ratio, and the effect was singular in each case and gave different results.     

Modification of the Ultrastable Y Zeolite with Citric Acid in the Unbuffered System

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Preparative Procedure for the Reduction of Substituted Nitroarenes with Hydrazine Hydrate in the Presence of a Nickel–Cobalt Nanocatalyst

A preparative procedure has been proposed for the reduction of substituted nitroarenes with hydrazine hydrate in the presence of a nanocatalyst based on cobalt–nickel nanoparticles, which ensured selective formation of the corresponding anilines in 78–80% yield in 20–45 min.     

Effect of the State of a Surface Layer on the Properties of Pd–P Catalysts in the Hydrogenation of Alkylanthraquinones

Kinetics and Catalysis - X-ray photoelectron spectroscopy (XPS) was used to study the state of the surface layer of a Pd–P catalyst, which exhibits high selectivity in the hydrogenation of...     

Catalytic Activity of Polymetalorganosiloxanes Supported on Silica in the Metathesis of a C–Cl Bond

The catalytic activity of structurally different Cu- and Ni-containing polymetalorganosiloxanes supported on silica was studied using the reaction of C–Cl bond metathesis in the carbon tetrachloride–saturated hydrocarbon (n-decane) system as an example. Catalysts with low metal contents were found to exhibit the highest activity; an increase in the metal content resulted in a decrease in both conversion and specific activity. At the initial portions of kinetic curves, the reaction was described by first-order rate equations with respect to n-decane; the reaction was of fraction order with respect to CCl₄and catalyst. The activation energy of the process in the n-decane–carbon tetrachloride system on a copper-containing network catalyst was 23 ± 2 kcal/mol. The mechanism of catalysis on immobilized catalysts from the above class is discussed.     

Ionic Hydrogenation of α,β-Unsaturated Ketones with Cyclohexane in the Presence of Aluminum Halides

4-Methyl-3-penten-2-one, 3-hepten-2-one, 3-methyl-1-phenyl-2-buten-1-one, 4-(2,4-dichlorophenyl)-, 4-(4-hydroxyphenyl)-, 4-(4-methoxyphenyl)-, 4-(2-hydroxyphenyl)-, and 4-(4-dimethylaminophenyl)-3-buten-2-ones, and 3-(4-methoxyphenyl)-1-phenyl-2-propenone react with cyclohexane in the presence of excess aluminum chloride or aluminum bromide in CH2Cl2 or CH2Br2, respectively, at room temperature to form the corresponding saturated ketones in high yields. Using 4-phenyl- and 4-(4-methoxyphenyl)-3-buten-2-ones as examples, it was shown that the reaction pattern does not change in going from the Lewis acids AlCl3 and AlBr3 to proton-donor acid system CF₃SO₃H-SbF₅. The reactive intermediates are likely to be C-protonated complexes of ,-unsaturated ketones with aluminum halides or their O,C-diprotonated analogs.     

Detection and Determination of Released Ions in the Presence of Nanoparticles: Selectivity or Strategy?

Metallic nanoparticles can release ionic species, but also both species can occur in the same samples. Therefore, there is a need of efficient and cost‐effective methods to determine these ionic species in the presence of the corresponding nanoparticles. Electroanalytical techniques open the door to this selective detection of NPs and their ions. In this work, a methodology that allows the direct determination of ionic silver (Ag⁺) in the presence of silver nanoparticles based on anodic stripping voltammetry was implemented. Silver nanoparticles were determined, after acidic digestion of the sample, by difference with respect to the total content of silver. The method was validated in terms of specific identification of silver ions, linearity, working range, limit of detection, limit of quantification, recovery, repeatability and ruggedness. All parameters are adequate for an analytical method following Eurachem recommendations. The validated method was used to determine the concentration of Ag⁺ and total silver in two commercial products of colloidal silver. The results were compared with those obtained by atomic absorption spectrometry in combination with an ultrafiltration step for isolation of ionic silver. There were no significant differences in the results. The proposed methodology benefits from the intrinsic selectivity of the electroanalysis methods, allowing to eliminate the steps of pretreatments of the samples, which are necessary in other techniques. The novelty of the article lies in the direct determination of Ag (I) ions in the presence of AgNPs, without the use of previous separation steps.     

Production of Methyl Acetate from Methanol in Vapor-Phase Tandem Reactions on Supported Copper–Nickel Catalysts

Theoretical and Experimental Chemistry - A method is proposed for the production of methyl acetate by combining vapor-phase reactions of methanol decomposition on a CuO-NiO-ZnO/Al2O3/cordierite...     

Note a Kinetic Study of the Photopolymerization of N,N Methylenebisacrylamide Initiated by N‐Bromo‐Succinimide in the Presence and Absence of Isopropyl Alcohol

The photopolymerization of N,N′‐methylenebisacrylamide has been studied with N‐bromosuccinimide as photoinitiator in the presence and absence of isopropyl alcohol (ISP). The rate of polymerization in the presence of ISP was found to be very high, and this is explained on the basis of the relative reactivities of the initiating radicals. A probable mechanism consistent with the observed results is proposed and discussed.     

Facile and Large-Scale Fabrication of Sub-3 nm PtNi Nanoparticles Supported on Porous Carbon Sheet: A Bifunctional Material for the Hydrogen Evolution Reaction and Hydrogenation

Facile and large-scale preparation of materials with uniform distributions of ultrafine particles for catalysis is a challenging task, and it is even more difficult to obtain catalysts that excel in both the hydrogen evolution reaction (HER) and hydrogenation, which are the corresponding merging and splitting procedures of hydrogen, respectively. Herein, the fabrication of ultrafine bimetallic PtNi nanoparticles embedded in carbon nanosheets (CNS) by means of in situ self-polymerization and annealing is reported. This bifunctional catalyst shows excellent performance in the hydrogen evolution reaction (HER) and the hydrogenation of p-nitrophenol. Remarkably PtNi bimetallic catalyst with low metal loading (PtNi₂@CNS-600, 0.074 wt % Pt) exhibited outstanding HER activity with an overpotential as low as 68 mV at a current density of 10 mA cm⁻² with a platinum loading of only 0.612 μg_Pt cm⁻² and Tafel slope of 35.27 mV dec⁻¹ in a 0.5 m aqueous solution of H₂SO₄, which is comparable to that of the 20 % Pt/C catalyst (31 mV dec⁻¹). Moreover, it also shows superior long-term electrochemical durability for at least 30 h with negligible degradation compared with 20 % Pt/C. In addition, the material with increased loading (mPtNi₂@CNS-600, 2.88 % Pt) showed robust catalytic activity for hydrogenation of p-nitrophenol at ambient pressure and temperature. The catalytic activity towards hydrogen splitting is a circumstantial evidence that agrees with the Volmer–Tafel reaction path in the HER.     

A General Catalyst Based on Cobalt Core–Shell Nanoparticles for the Hydrogenation of N-Heteroarenes Including Pyridines

Herein, we report the synthesis of specific silica-supported Co/Co₃O₄ core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased.     

A Study on the Simultaneous Determination of Copper and Tin in the Presence of Lead

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Stereoselective Hydrogenation of Thymol over Rh/alumina in the Presence of β:-cyclodextrin and its Derivatives

Stereoselective hydrogenation of thymol over Rh/alumina in the presence of various equivalents of -cyclodextrin (-CD) and itsderivatives in the solid state was studied. Hydrogenation of thymol in the absence of -CD gave 76.8% epimeric alcohols with a menthol/neomenthol (M/N) ratio of 5.6 and an alcohol/ketone ratio of 4.5, whereas the presence of 0.1 equivalent (to thymol) of -CD gave rise to 94.6% of epimeric alcohols with a M/N ratio of 6.3 and an alcohol/ketone ratio of 45.4. The effect of -cyclodextrin and its derivatives on the modification of the yield and the proportion of epimeric alcohols formed were found to be the salient features of this investigation. Inclusion complexation of thymol by -CD studied by UV-Visible spectroscopyindicated a 2:1 stoichiometry ofthymol: -CD complex with a binding constant value of 480 ±40 M^-2.     

Oxidation of Sulfides with N‐Bromosuccinimide in the Presence of Hydrated Silica Gel

An efficient and highly selective procedure for oxidation of sulfides to sulfoxides with N‐bromosuccinimide (NBS) in the presence of hydrated silica gel has been developed. Hydrated silica gel supplies the water necessary for decomposition of the intermediate bromosulfonium salt to the product, allowing the reaction to employ a nonaqueous media. Also, this procedure has increased the scope of the reaction by oxidizing a wider variety of sulfides, which was not possible until now.