T. N. Rostovshchikova

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.

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).

Mixed-valence copper complexes with the organic donors as catalysts for dichlorobutene isomerization

Abstract The formation of mixed-valence copper complexes with dialkyl sulfides or triphenylphosphine in the catalytic isomerization of dichlorobutenes was investigated kinetically and spectroscopically (UV–Vis, IR, EPR, NMR). These species were prepared both starting from Cu(I) and Cu(II) compounds. The complexes containing 3 or 4 copper ions in different oxidation states, substrate and donor molecules were found to play a key role in catalysis. Chlorolefins with allylic chlorine atom may stabilize mixed-valence complexes as bridging ligand between Cu(I) and Cu(II). The EPR spectra of these complexes provide the five-coordinated Cu(II) with a trigonal–bipiramydal geometry of coordination sphere. The simultaneous presence of Cu(I) and Cu(II) in polynuclear structure is proposed to favor the electron transfer step in the reaction mechanism.

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.

Interaction of hydrogen and oxygen on the surface of individual gold nanoparticles

Adsorption properties of gold nanoparticles on pyrolytic graphite were studied. Water molecules are formed due to the consecutive adsorption of hydrogen and oxygen on the nanoparticle surface. The energies of bonds between chemisorbed hydrogen, water, and gold were determined.

Distinctive Characteristics of Carbon Tetrachloride Addition to Olefins in the Presence of Copper Complexes with Donor Ligands

The interaction between CCl4and olefins with different structures is studied in the presence of copper complexes with P-, S-, and N-containing donor ligands. Kinetic and spectroscopic studies show that the ability of olefins to be coordinated to copper complexes governs the rate, the product composition, and the reaction mechanism. Depending on the olefin and the structure of the metal complex, either typical radical-chain reactions or processes without free radicals are observed.

SURFACE DENSITY OF PARTICLES IN THE DESIGN OF NANOSTRUCTURED CATALYSTS

A discussion is given for theoretical and experimental data confirming the correlation between the catalytic properties of supported catalysts based on metal nanoparticles, the existence of contacts between the particles, and the possibility of charge transfer between them. Laser electrodispersion was used to prepare model systems.

Unusual catalytic properties of nanostructured nickel films obtained by laser electrodispersion

Nanostructured nickel films deposited by laser electrodispersion onto a silicon (semiconducting) or thermally oxidized silicon (insulating) substrate show a remarkably high catalytic activity (of the order of 103–104 (mol product) (mol Ni)−1 h−1) in the isomerization of chlorinated hydrocarbons and olefin hydrogenation. The special properties of the laser-deposited films are likely due to the small size (2.5 nm), developed surface, and amorphism of the nickel particles, as well as to highly active, charged particles appearing on the insulating substrate. The latter result from thermal fluctuations of electrons between closely spaced particles. In a film deposited on silicon covered with a natural oxide layer, a significant role is also played by charge redistribution between the substrate and metal particles.

Structurally Organized Nanocomposites in the Catalysis of Chlorohydrocarbon Reactions

Catalysis by closely packed metal films containing monodispersed nanocluster ensembles was considered using the reactions of chlorinated hydrocarbons as an example; these reactions include a step of electron transfer from a catalyst to a reactant. A new laser electrodispersion technique was used for preparing films that consisted of spherical copper grains 5 nm in size coated with thin (0.7 nm) layers of copper(I) oxide with different particle packing densities on the surface of thermally oxidized silicon. A comparison of the catalytic activity of films with varied packing density in media with different permittivities allowed us to assume that the observed maximum activity of closely packed films was associated with the appearance of charged grains in the ensembles of interacting nanoparticles due to the thermal fluctuations of electrons between closely spaced grains.

Laser electrodispersion method for the preparation of self-assembled metal catalysts

Abstract Laser electrodispersion (LED) method makes possible to fabricate dense nanostructured catalysts with unique catalytic properties. In contrast to earlier laser ablation techniques, where nanoparticles were synthesized from vaporized matter, LED is based on the cascade fission of liquid metallic drops. Fabricated catalysts consist of ensembles of nanoparticles that are uniform in size and shape, amorphous and stable to coagulation. The catalytic activity of these self-assembled Pt, Ni, Pd, Au and Cu catalysts with extremely low metal content ( -3 mass.%) in hydrogenation and hydrodechlorination is several orders of magnitude higher compared to that for separated metal clusters, highly loaded metal films and supported catalysts prepared by usual methods.