D. A. Yavsin

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.

Effect of oxidation on the electrical properties of granular copper nanostructures

The structural and electrical properties of thin granular metal films obtained by laser electrodispersion were studied. Such structures, which consist of amorphous copper grains 5 nm in size, were established to be extremely stable against oxidation. For instance, when oxidized in air, copper grains were covered by Cu2O oxide shells about 1 nm thick after a period of a few days, after which further growth of the oxide in thickness stopped. The oxidized close-packed structures conduct current through intergrain tunneling electron transitions, whereas in partially oxidized structures the conduction involves tunneling electron hopping between conducting ensembles made up of several nanoparticles. It was shown that the size of the nanoparticles and of the conducting ensembles can be found by analyzing the temperature dependence of the conductivity and, independently, from the I–V characteristics of the films.

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).

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.

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.

Electron transport in monodisperse metal nanostructures

Electron transport in monodisperse granular Cu, Ni, and Pd structures with conduction near the percolation threshold is investigated. An activation conduction law is observed in the oxidized Cu structures, whereas the Efros-Shklovskii law is observed in the initial Cu structures and in the Ni and Pd structures. This behavior is discussed within the framework of a model in which variable range hopping conduction is considered with regard to both the disorder potential and spread of the sizes of grain assemblies.

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.

Formation of Structures from Amorphous Metallic Nanoparticles by Dispersing Metal Drops Continuously Charging in an Electron Beam

The formation of amorphous metal nanoparticles by the method of electrohydrodynamic dispersion is studied. In this method, fine liquid metal drops are generated, charged in an electron beam to an unstable state, and dispersed into nanometer droplets. Rapid cooling of these nanometer droplets results in the formation of amorphous metal nanoparticles. The chief problem in the formation of such particles is that it is difficult to charge molten metal drops to an unstable state, since the bombardment of the drop by an electron beam may cause intense emission of electrons. To overcome this difficulty, the drops are charged by a beam of slow electrons. Charging proceeds in such a way that the electron energy rises with the drop’s charge. It is shown that this method makes it possible to obtain granulated films made up of amorphous metal particles. Copper films with a nanoparticle mean size of 2 nm and a small dimensional variation are prepared.

A study of lithium insertion into electrodes with thin gold films

The process of lithium insertion into thin gold films is studied. It is found that lithium is reversibly inserted with the formation of compounds, which are close to Li1.5Au in their average composition. The long-term cycling leads to the breakdown of gold layer (and corresponding decrease in the electrode capacity), which is associated with considerable volume changes due to lithium insertion.