Search

The anodic oxidation of the carbon felt Carbonetcalon results in the formation of surface defects which serve as centers of strong adsorption of PdII, NiII, and CuII ions. The electrochemical reduction of adsorbed ions makes it possible to obtain metallic catalysts, which undergo multiple redox cycles without loss of metal. The catalysts are characterized by high dispersity of the reduced phase, high adsorption capacity with respect to hydrogen, and 100% selectivity in hydrogenation of acetophenone.

The reaction of carbon monoxide with the surface of Ni, Pd, and Ni-Pd catalysts, deposited on γ-Al2O3, was investigated at 25°C by IR spectroscopy in conjunction with an adsorption volumetric technique. The IR spectra contained the following absorption bands (v, cm−1): 2020–2100 (AB1) (linear and subcarbonyl forms of adsorbed CO); 1945–1985 (AB2) (bridging); 1920–1940 (AB3) with a shoulder at 1870–1885 (AB4) (bridging and many-center). In the spectrum of Ni the absorption band AB5 appears at 1770–1780 (CO-Ni+). It appears with surface coverage a ≥ 1.3 mole CO/mole eM. The optical density (A) of AB1 for Ni97Pd3 is appreciably higher than for the other investigated samples. In the Ni-Pd catalysts the intensity of AB2 in relation to AB1 is higher than in nickel. The introduction of K+ ions into the support of the bimetallic sample reduces the optical density of AB1. In modified Ni-Pd-K the AB3 and AB4 bands disappear.

The use of an Ni-Pd/Al2O3 catalyst in the synthesis of C1-C4 hydrocarbons from CO and H2 permits us to increase the selectivity and total yield of these products by a factor of 1.5–2.0 relative to the corresponding nickel and palladium catalysts. The optimal temperatures and CO/H2 ratios for obtaining hydrocarbons were determined. A structure was proposed for the active sites of the bimetallic catalyst.

The potential at which Pd is deposited on vitreous carbon has a strong influence on the activity of the catalyst in the cathodic evolution of H2 and the electrohydrogenation of acetophenone. The most effective catalyst is Pd deposited at E=0.6 V.

In liquid-phase hydrogenation of ethyl acetoacetate on bimetallic Ni-Pd catalysts supported on Al2O3, the reaction rate increases sharply and passes through a maximum with an increase in the concentration of Pd. The change in the rate of hydrogenation with a change in the composition of the catalysts is not due to a change in the dispersion of the metallic phase in them or enrichment of their surface with one of the metals.

The effect of support content and composition of supported metal phase on the crystallite size, phase composition and catalytic properties of supported Ni and Cu−Ni catalysts has been investigated. It has been established that with increasing metal content, crystallite sizes and enantioselectivity increase. Copper added to Ni catalysts decreases metal phase dispersity and enantioselectivity.

1. A study was made of the asymmetric hydrogenation of the oxime of R-menthyl phenylglyoxylate on Pd(OH)2/C catalyst at atmospheric pressure and 25° in ethanol. 2. The stereodirectivity of the process changes during reaction; the possible stereochemical mechanism of the addition of hydrogen is discussed.

The rate of formation of the excess of one enantiomeric product in the enantioselective hydrogenation of ethyl acetoacetate (EAA) and acetylacetone (acac) on a Raney copper catalyst modified with chiral aminoacids (AmA) correlates with the formation constants of the mixed complexes [CU EAA AmA] and [Cu acac AmA].

1. Using adsorption, thermal desorption, and isotopic methods the authors have investigated the state of hydrogen present on the surface of Ru/Al2O3, Ru/SiO2, and Ru black catalysts. 2. Hydrogen can be adsorbed very strongly on the surface of Ru catalysts, and removed only at elevated temperatures. The amount of strongly adsorbed hydrogen sharply increases in going from Ru black to deposited catalysts. 3. Hydrogen adsorbed on Ru can spread over the carrier surface and take part in exchange with the carrier OH groups.

1. Synergism has been found in the enantioselective hydrogenation of ethyl acetoacetate on copper-ruthenium catalysts supported on aerosil and modified with (+)-tartaric acid. 2. A hypothesis has been advanced to explain the activating effect of ruthenium on the copper.

1. The IR spectra have been obtained of RR-(+)-tartaric acid chemisorbed on Cu, Ni, and Cu-Ni catalysts supported on Aerosil. 2. We have considered the probable structure of the asymmetric clusters that carry out asymmetric hydrogenation, and of the intermediate heteroligand complexes through which the enantioselective reaction proceeds.

Studies of the effect of preparation conditions on the activity and enantioselectivity of asymmetric Cu−Ni catalysts have revealed their great dependence and two maxima in the dependence of the optical yield on the pH of the modifying solution. Cu−Ni catalysts are shown to have similar catalytic properties in a wide range of their Cu content.

1. The catalytic properties of CNC depend on the conditions of preparation. The simultaneous formation of Cu and Ni and their alloy occurs during the-reduction process of CNC. 2. The appearance of a cluster effect is observed for the enantioselective hydrogenation on CNC.

1. The catalytic and asymmetrizing properties of copper-nickel catalysts deposited on Aerosil in the hydrogenation of acetylacetone have been investigated. 2. The adsorption of acetylacetone on these catalysts modified with RR-(+)-tartaric acid and the unmodified catalysts has been studied by IR spectroscopy. 3. A synergistic effect of the catalytic, asymmetrizing, and adsorption properties of the copper-nickel catalysts has been found. 4. The results obtained are in harmony with the idea of the occurrence of the asymmetric hydrogenation of acetylacetone through a mixed-ligand complex of the [substrate-modifying agent-catalyst] type.

The correlation between the asymmetrizing and catalytic activities of ruthenium catalysts of different origins has been studied. The preparation of the catalyst and the nature of the support have been shown to have a considerable effect on the specific activity of the catalyst and its asymmetrizing ability.

1. An x-ray and thermogravimetric study was made of the phase composition of a skeletal ruthenium that was obtained by the decomposition of a Ru−Al alloy (30% Ru) with caustic alkalis. It was found that, besides highly dispersed metallic ruthenium, the catalyst contains bayerite. 2. Skeletal ruthenium catalyst when heated to 600° decomposes in stages due to dehydration of the bayerite. 3. The same as in the case of the Ni−Al alloy, complex aluminum salts are formed during the leaching of the aluminum from a Ru−Al alloy, which then decompose with the formation of aluminum trihydroxide.

1. It has been established that skeletal Cu-Pd catalysts contain phases of Pd and Cu or a Pd-based solid solution, and also Pd, and Al2O3·3H2O. 2. The adsorption of hydrogen on these catalysts in a 0.1 N H2SO4 solution has been investigated, and it has been found that the quantity of hydrogen adsorbed on the skeletal copper-palladium catalysts drops off very rapidly as the Pd content in the Metallic phase is increased from 5.1% to 15.1% (at.). 3. The possibility of catalytic activation of the copper by the palladium has been demonstrated, and also the capability of the skeletal copper-palladium catalysts for performing enantioselective hydrogenation.

For Raney Cu-Ru and Cu-Pd catalysts non-additive changes in the strength of the catalyst-hydrogen bond and in the catalytic activity and enantioselectivity were found to occur with changing composition, indicating the presence of a ligand effect in these systems.

1. We have prepared a skeletal Cu-Pd catalyst modified with tartaric acid, on which there is 100% selectivity in the hydrogenation of ethyl α-acetylamino-β-ketobutyrate with a yield of N-acetyl-allo-threonine ethyl ester of about 90%. 2. It is shown that the nature of the metal phase of the catalysts has an effect on their activity, selectivity, and diastereoselectivity in this process.

1. The kinetics of the hydrogenation of acetoacetic ester on skeletal copper catalyst in the liquid phase was studied. The observed reaction rate is strongly dependent on the hydrogen pressure and the temperature. 2. A scheme was proposed for the progress of the studied reaction along three routes.

A mixed Cu-Ni (1∶1) catalyst, deposited on aerosil and modified with D-(+)-tartarie acid, was obtained, which is active in theselective stereoselective hydrogenation of acetylacetone to the (-)-ketol. The optical yield of the ketol is 9.1% at 133°.

1. Mixed skeletal Cu-Ru catalysts, which contain 0.01–0.5% Ru, have a much smaller asymmetrizing capacity than skeletal copper and ruthenium catalysts. 2. The activity of the mixed skeletal catalysts is substantially greater than the activity of skeletal copper.

1. Skeletal copper-ruthenium catalysts are composed of copper, ruthenium, bayerite, and gibbsite phases. 2. The change curves of the copper-ruthenium catalysts were taken, and from them were determined the specific surface areas of the ruthenium phases and the average size of the ruthenium crystallites. 3. A complex relationship was found to exist between the dispersity of ruthenium and its amount in a mixed catalyst.

The properties of immersed bimetallic Cu−Pd and Ni−Pd catalysts have been examined. They depend on both the nature of support and the method for introducing metal components onto support.

Pronounced synergism of the asymmetric effect of chiral copper-palladium catalysts related to manifestation of a ligand effect was found.

1. A study was made of the asymmetrizing activity of asymmetric Ru/SiO2 catalyst samples that had been modified with (+)-tartaric acid in the liquid-phase hydrogenation of ethyl acetoacetate. 2. The sample that contains Ru as crystallites with a size of 45 A has the highest asymmetrizing activity. 3. Taking into consideration the characteristics of asymmetric hydrogenation, an explanation was offered for the observed experimental data.

Enantioselective hydrogenation with different chiral catalytic systems has been thought to proceed through an intermediate complex (metal-modifier-substrate). The heteroligand complexes of Cu, Co and Ni with chiral amino acids(AmA) and aoetylacetone (AA) or ethyl acetoacetate (EAA) have been studied by chiroptical methods as models of the intermediates. The correlation of the degree of conformational distortion of carbonyl compound with configuration of its hydrogenation product has been observed. The enantioselective hydrogenatin of AA and adsorption on Cu-Ni/Aerosil catalysts have been studied. The correlation between the covalency of COO-metal bond and optical yield was found. The step-by-step mechanism of enantioselective reductive aminolysis of -oxa-zolin-5-ones with Pd and Rh catalysts has been investigated and it has been concluded that the chiral nucleophile may act as a modifier of the catalysts.

1. Copper tartrate complexes that partially go into solution are formed on the surface of a copper catalyst when skeletal copper is modified with (2R,3R)-(+)-tartaric acid. 2. The character of the modifier-catalyst bond is close to the character of the modifier-metal bond in the corresponding complex.