A. Yu. Vasil’kov

Selective hydrogenation of phenylacetylene into styrene on gold nanoparticles

Gold nanoparticles (2–10 nm) supported on γ-Al2O3 exhibit high activity and stability in the hydrogenation of phenylacetylene into styrene in the phenylacetylene-styrene mixture. The selectivity of the catalyst is particle size-dependent: the styrene-to-ethylbenzene molar ratio in the reaction products increases from 2 to 30 as the average gold particle size decreases from 8 to 2.5 nm. The selectivity of phenylacetylene hydrogenation correlates with the selectivity of phenylacetylene adsorption on Au/γ-Al2O3 from the phenylacetylene-styrene mixture.

Synergism of the catalytic effect of nanosized gold-nickel catalysts in the reaction of selective acetylene hydrogenation to ethylene

Gold and nickel nanoclusters immobilized on aluminum oxide exhibited high activity in the reaction of acetylene hydrogenation to ethylene with molecular hydrogen at temperatures from 20 to 64°C. The reaction selectivity on Au-Ni nanocomposites with metal concentrations from 0.02 to 0.36 wt % was no lower than 99.99%, and the stability of catalysts was retained for at least 12 h. The simultaneous presence of gold and nickel in the systems resulted in the synergism of their catalytic effects: acetylene conversion on layer-by-layer immobilized metal clusters was higher than the total conversion on individual gold and nickel clusters. The dependence of the conversion of acetylene on bimetallic catalysts on the Au : Ni ratio exhibited an extremal character.

Allylic isomerization of allylbenzene on nanosized gold particles

Nanosized gold particles immobilized on γ-Al2O3 exhibited catalytic activity in the allylic isomerization reaction of allylbenzene. As the size of gold nanoparticles was decreased from 40 to 2 nm, their specific activity per surface gold atom nonmonotonically increased from 0.5 to 110 (mol products) (mol Ausurface)−1 h−1. The particles greater than 40 nm were practically inactive.

Hydrocarbon Adsorption on Gold Clusters: Experiment and Quantum Chemical Modeling

Heats of adsorption Q of n-alkanes C6–C9 on ZrO2 modified with gold and nickel nanoparticles were determined experimentally. The Q values were found to be higher on average by 7 kJ/mol on the modified samples as compared to the pure support. Density functional theory with the PBE functional and the pseudopotential for gold effectively allowing for relativistic corrections was used to model the adsorption of saturated hydrocarbons on Au and Au + Ni, as exemplified by the interaction of alkanes C1–C3 with Aum, Aum − 1Ni (m = 3, 4, 5) clusters as well as the interaction of C1–C8 with Au20. Based on the calculation results, the probable coordination centers of alkanes on nanoparticle surfaces were found to be vertices and edges, whereas face localization was less probable.

X-ray photoelectron spectra and structure of composites prepared via deposition of Au, Ni, and Au + Ni nanoparticles on SiO2 from colloidal solutions in triethylamine

Monometallic (Au and Ni) and bimetallic (Au + Ni) nanoparticles deposited on SiO2 from colloidal solutions in triethylamine have been studied by x-ray photoelectron spectroscopy (XPS). The solutions were prepared through vapor-phase metal synthesis. We have determined the basic parameters of the core-level and valence-band XPS spectra of the Au/SiO2, Ni/SiO2, and Au-Ni/SiO2 systems. The results indicate that the Au in these systems is in the Au(0) state, while Ni is oxidized to Ni(II). The Au/SiO2 and Au-Ni/SiO2 samples differ little in the shape of the Au 4f peak. In the Au-Ni/SiO2 system, the Ni 2p3/2-Au 4f7/2 binding energy difference is 0.3 eV larger and the Ni 2p3/2 peak is narrower than those in the monometallic samples. The effects characteristic of the bimetallic system may be due to the interaction between Ni and Au or may be interpreted as evidence that the Au particles level off the potential relief on the SiO2 surface.

Composite materials for medical purposes based on polyvinylpyrrolidone modified with ketoprofen and silver nanoparticles

A method for obtaining composite medical materials based on polyvinylpyrrolidone (PVP K15) modified with ketoprofen in a medium of supercritical carbon dioxide and with Ag nanoparticles prepared by metal vapor synthesis is developed. A system in which ketoprofen and Ag nanoparticles with an average size of ∼16 nm are uniformly distributed over the bulk of PVP is obtained. It is found that the yield of ketoprofen from the composite in the physiological solution is higher than that for an analogous system obtained by mechanical mixing of the components.

Categorization system of nanofillers to polymer composites

The paper deals with a systematic categorization of nanofillers in terms of their effect arising upon introduction into polymer composites of tribological applications. The authors study the nature of this effect and the tribological behavior of different types of nanofillers acting in composites and exhibiting either a tribochemical effect or a discrete surface one. Nanofillers having an indirect influence on friction and intercalation compounds are also studied.

Catalysis of Olefin Hydrogenation and Allylic Isomerization by Immobilized Gold Nanoclusters

Gold nanoparticles immobilized on carbon and oxide supports showed catalytic activity in the hydrogenation and allylic isomerization of alkenes and arylalk-1-enes. The catalysts were active only in the case when the average size of metal particles did not exceed 30 nm. Hydrogenation was accompanied by the allylic isomerization of the substrate. Under chosen conditions, the ratio of hydrogenation to isomerization rate was close to 1: 2. The activity of gold nanoparticles immobilized on oxide catalysts increases with an increase in their acidity.

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.

A density functional study of the structure and potential energy surface of dibenzenechromium and its alkylated derivatives

Density functional calculations were performed with the nonempirically constructed PBE functional and TZ2p basis set to study the potential energy surfaces of several dibenzenechromium derivatives containing methy1 and tert-buty1 groups in aromatic ligands. The method was shown to correctly describe the structure and intramolecular dynamics of bis-arenechromium complexes. It allows barriers to rotation about the metal-ligand bond to be calculated and detailed information to be obtained about the shape of the potential curves that correspond to this rotation. The potential energy surfaces of polymethylated dibenzenechromium derivatives contained several minima close in energy; these minima largely corresponded to eclipsed conformers. The potential curves for rotation about the metal-ligand bond in dibenzenechromium and its methylated derivatives reveal the presence of staggered conformers as transition states. Irrespective of the number of methyl groups present in both ligands, we observed no substantial changes in barrier heights, which were about 1 kcal/mol. Conversely, the introduction of bulky tert-butyl groups destabilized eclipsed conformations. Ensuing steric strain caused substantial out-of-ring-plane displacements of the Cipso-t-Bu bonds away from the chromium atom, distorted aromatic ring planarity, and substantially increased barriers to rotation, to 8–10 kcal/mol.