E. S. Lokteva

Catalytic hydrodehalogenation of organic compounds

Recent results on hyd rode halogenation (HDH) of alkyl halides, freons, aryl halides, polychlorinated derivatives of benzodioxines and biphenyls, and other compounds in the presence of heterogeneous and homogeneous catalysts are generalized, Effective and selective hydrodehalogenation proceedsvia anion or radical anion intermediates. Special attention is given to the nature of the source of the hydrogen replacing the halogen.

The hydrodechlorination of chlorobenzene in the vapor phase in the presence of metal-carbon nanocomposites based on nickel, palladium, and iron

Metal-carbon nanocomposites based on nickel, palladium, and iron and bimetallic palladium-nickel-carbon nanocomposites were for the first time used as catalysts of hydrodechlorination of chlorobenzene in the vapor phase in the atmosphere of hydrogen. Nickel and Pd-Ni nanoparticles completely coated by a carbon layer not only were stable to oxidation and agglomeration but also exhibited considerable activity in hydrodechlorination of chlorobenzene at temperatures much lower than those at which dechlorination on carbon carriers occurred. The dependence of catalytic properties (activity, selectivity, and stability) on temperature and nanocomposite composition was studied. Depending on the nature of the metal, the composition of bimetallic particles and temperature the selectivity could be changed, and the reaction could be directed toward the formation of benzene or cyclohexane. Carbon coating was stable under reaction conditions at least up to 350°C and did not hinder hydrodechlorination. Substrate adsorption likely occurred on the outside carbon surface of composite particles. The activity and structure of Ni@C composite remained almost unchanged after triple cycling over the temperature range from 50 to 350°C in a flow system.

High catalytic activity and stability of palladium nanoparticles prepared by the laser electrodispersion method in chlorobenzene hydrodechlorination

Palladium nanoparticles deposited on thermally oxidized silicon and on the carbon support Sibunit by the laser electrodispersion method are extremely active in the gas-phase hydrodechlorination of chlorobenzene at 100–200°C. High conversion of chlorobenzene (above 90%) has been achieved with catalysts with an unusually low metal content (from 10−4 to 10−3 wt %). The cyclohexane-to-benzene ratio in the reaction products depends on the process duration, palladium content, and support nature. According to X-ray photoelectron spectroscopy (XPS) data, palladium in the catalysts retains its metallic state over a long time under the reaction conditions. Possible causes of the high catalytic activity (105 mol (mol Pd)−1 h−1) of the palladium nanoparticles and their stability to chlorination are discussed.

Palladium on ultradisperse diamond and activated carbon: The relation between structure and activity in hydrodechlorination

Ultradisperse diamond was studied as a promising carrier for Pd-containing hydrodechlorination catalysts. Transmission electron microscopy, temperature-programmed reduction, and the adsorption method were used to study catalysts on ultradisperse diamond and activated carbon and a commercial catalyst from Fluca. Catalyst activities in multiphase hydrodechlorination of chlorobenzenes were compared. The activity of Pd-containing catalysts on ultradisperse diamond was found to be several orders of magnitude higher than that of Pd catalysts on activated carbon.

C-C bond formation during hydrodechlorination of CCl4 on Pd-containing catalysts

Catalytic transformations of CCl4 in a flow-type system in vapors under 150–230°C in the presence of carbon and titania supported Pd catalysts after special treatment has been studied. Under such conditions not only hydrodechlorination products were formed, but also a mixture of saturated and unsaturated hydrocarbons having chain-length up to C5.

Hydrogen dissociation catalyzed by carbon-coated nickel nanoparticles: experiment and theory.

Based on the combination of experimental measurements and first-principles calculations we report a novel carbon-based catalytic material and describe significant acceleration of the hydrogenation of magnesium at room temperature in the presence of nickel nanoparticles wrapped in multilayer graphene. The increase in rate of magnesium hydrogenation in contrast to a mix of graphite and nickel nanoparticles evidences intrinsic catalytic properties of the nanocomposites explored. The results from simulation demonstrate that doping of the metal substrate and the presence of Stone-Wales defects turn multilayer graphene from being chemically inert to chemically active. The role of the size of the nanoparticles and temperature are also discussed.

The synthesis, structure, and properties of carbon-containing nanocomposites based on nickel, palladium, and iron

Nickel, iron, palladium, and bimetallic nickel-palladium nanoparticles encapsulated in carbon were synthesized by contactless levitation fusion of metals in a magnetic field in a flow of an inert gas containing a hydrocarbon. The products were characterized by X-ray diffraction, differential thermal analysis, thermogravimetry, high-resolution transmission electron microscopy, and adsorption. A layered carbon shell preventing agglomeration and oxidation formed on the surface of nickel- and iron-containing particles. The size of particles depended on preparation conditions and could be of 5–15 nm.

Laser electrodispersion as a new chlorine-free method for the production of highly effective metal-containing supported catalysts*

Laser electrodispersion (LED) of metals is a promising technique for the preparation of heterogeneous catalysts as an alternative to wet impregnation of supports with the corresponding salt solutions. The LED technique can be used to deposit highly active chloride- and nitrate-free metal nanoparticles onto carbon or oxide supports. We report preparation and properties of new Ni-, Pd-, and Au-containing alumina-supported catalysts with low metal loadings (10–3–10–4 % mass) and their comparison with the previously studied carbon (Sibunit) supported systems. The catalysts demonstrate high stability and extremely high specific catalytic activity (by 2–3 orders of magnitude higher than for traditional catalysts) in the gas-phase hydrodechlorination (HDC) of chlorobenzene (CB).

Formation of C1-C5 hydrocarbons from CCl4 in the presence of carbon-supported palladium catalysts

Along with hydrodechlorination, the formation of C1 and higher hydrocarbons takes place in a flow system in the presence of catalysts containing 0.5–5.0% Pd supported on a Sibunit carbon carrier at 150–230°C. In the entire range of conditions examined, the reaction products are primarily methane, C2–C4 hydrocarbon fractions, and C5 traces. The catalysts are stable in operation, and a high conversion of CCl4 was retained for a long time interval. The nonselective formation of linear and branched hydrocarbons is indicative of a radical mechanism of the process.

Ultradispersed diamond as a new carbon support for hydrodechlorination catalysts

The properties of palladium and nickel catalysts supported on ultradispersed diamond (UDD) were studied in the vapor-phase hydrodechlorination (HDC) reaction of chlorobenzene and the multiphase HDC of polychlorobenzenes. The catalysts on UDD exhibited a number of advantages: the vapor-phase HDC of chlorobenzene on Ni/UDD occurred at lower temperatures, and the multiphase HDC of chlorobenzene, 1,3,5-trichlorobenzene, and 2,4,8-trichlorodibenzofuran on Pd/UDD occurred more rapidly than that on catalysts supported on activated carbon. The structure of the catalysts and the electronic states of the active components were studied using IR spectroscopy, temperature-programmed reduction, and adsorption techniques. It was found that the properties of the catalysts depend on the electronic state of palladium, which depends on its concentration in the sample; the structural properties, which are responsible for the accessibility of the active surface to adsorption; and the presence of other metal impurities.