E. V. Golubina

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.

Activity of Au, Ni, and Au–Ni Catalysts in the Water-Gas Shift Reaction and Carbon Monoxide Oxidation

Au/Al2O3, NiOx/Al2O3, and (Au + NiOx)/Al2O3 composites have been prepared by ion exchange and impregnation. Their structural and electronic properties, including the size and shape of supported metal particles and the oxidation state and ligand environment of the Au and Ni atoms, have been investigated. The catalytic action of Au/Al2O3, NiOx/Al2O3, and (Au + NiOx)/Al2O3 in the water-gas shift reaction and carbon monoxide oxidation is reported. At 300–450°C, the CO conversion over (Au + NiOx)/Al2O3 exceeds the sum of the CO conversions over the monometallic catalysts Au/Al2O3 and NiOx/Al2O3 by a factor of 2–3. An explanation is suggested for the nonadditive increase in the CO conversion over the Au-Ni catalysts.

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.

Hydrodechlorination of chlorobenzene in the presence of Ni/Al2O3 prepared by laser electrodispersion and from a colloidal dispersion

The low-percentage Ni/Al2O3 catalysts with active metal contents of 0.0002–0.1 wt % were prepared using the laser electrodispersion (LED) method and by means of supporting from a colloidal dispersion (CD). Their composition and physicochemical properties were determined by atomic absorption spectrometry, transmission electron microscopy (TEM), and XPS. With the use of TEM, it was found that average size of nickel particles in the LED catalysts was smaller than that in the CD catalysts. According to XPS data, the supporting of a metal onto a substrate by the LED method makes it possible to obtain samples containing Ni metal with a low active metal content (0.03 wt %). They exhibited a high initial activity in the hydrodechlorination reaction of chlorobenzene in a vapor phase, which was performed in a flow system at temperatures of 100–350°C. The CD catalysts were active in this reaction only at temperatures of 300–350°C. Reductive treatment led to the deactivation of LED catalysts and increased the activity and stability of samples prepared by supporting from a CD. The possible reasons for the observed changes are considered.

Chlorobenzene hydrodechlorination catalyst prepared via the pyrolysis of sawdust impregnated with palladium nitrate

Abstract(7% Pd)/C catalysts have been prepared by the pyrolysis of untreated sawdust and sawdust washed with an acid to remove of Group I and II metal impurities, both impregnated with palladium nitrate. Studies by transmission electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction have demonstrated that the dominant palladium species in the catalysts is 2–5 nm Pd0 particles, there is no PdO on the surface, and the catalyst bulk contains small amounts of larger (10–20 nm) PdO particles. The catalysts are active in chlorobenzene hydrodechlorination in a fixed-bed flow reactor and ensure 100% conversion of the substrate into benzene in the temperature range from 250 to 350°C. At lower temperatures (150–200°C), the catalyst containing calcium is the most active and the sample subjected to reduction after pyrolysis shows the lowest activity.