Effect of γ-irradiation on the catalytic activity and selectivity of γ-alumina II. Conversion of isopropanol

The catalytic conversion of isopropanol was conducted over a poorly crystalline -alumina irradiated with different doses of -rays (25–150 Mrad). The catalytic reaction was carried out at 180–400°C in a flow technique under atmospheric pressure. The results showed that the dose of 25 Mrad resulted in a decrease of about 50% of the dehydration activity which suffered a further slight decrease upon irradiation at a dose of 50 Mrad. Increasing the dose in the range of 50–150 Mrad effected an increase in the dehydration activity reaching a maximum limit at 100 Mrad, then decreased abruptly by a dose of 150 Mrad. -irradiation led also to creation of some active sites contributing in dehydrogenation of isopropanol to producing acetone. These results were discussed in terms of removal of Brönsted acidity (25–50 Mrad), responsible for the dehydration reaction and to transformation of Lewis to Brönsted acidity (100 Mrad) by the action of liberated water from the dehydration reaction. The drop in dehydration activity due to irradiation at 150 Mrad might result from an efficient removal of the Brönsted acid sites created. The induced dehydrogenation activity of irradiated aluminas was attributed to creation of some electron-donor centers.     

Preparation of L-asparagine complex of technetium-99m

Attempts have been made to employ magnesium oxide as the preconcentration agent for determination of trace metal sin seawater by neutron activation analysis. Hydrous magnesium oxide can efficienthy adsorb most cationic transition metals and rare earths in a simple water system. The adsorption behavior is believed to depend mainly from the association of the cationic species of the metals with MgO ₂ ^2– adsorbent. In seawater matrix some of the metal ions such as Hg²⁺, Ni²⁺, etc. may become inefficiently adsorbed owing to the formation of highly stable metal-chloro complexes with chloride ion. Usually the adsorption efficiencies of the metals can be recovered to be as high as the case in the simple water system if an acidified seawater (to pH1) is subjected to the adsorption experiment. In practice, a large volume of seawater (5 1) is stirred with a small amount of hydrous MgO (1 g). Thereafter, the trace metals adsorbed MgO is separated and taken to be neutron activated. The abundant sodium ion and ubiquitous bromide ion can be obviated by the adsorption process, thereby beneficial to the -spectrometry of the metals enriched on MgO.     

In Situ IR Spectroscopic Studies on Molybdenum Nitride Catalysts: Active Sites and Surface Reactions

Recent IR spectroscopic studies on the surface properties of fresh Mo₂N/-Al₂O₃ catalyst are presented in this paper. The surface sites of fresh Mo₂N/-Al₂O₃, both Mo⁺ (0<<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm^-1, due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo₂N/-Al₂O₃ behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo₂N/-Al₂O₃ catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo₂N/-Al₂O₃ catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.     

Adsorption and Electrochemical Behavior of Cobalt Tetra(p-methoxyphenyl)porphyrin at Anisotropic Pyrographite

The electrochemical behavior and electrocatalytic activity of cobalt tetra(p-methoxyphenyl)porphyrin (CoTMPP) adsorbed at anisotropic pyrographite in the reaction of oxygen electroreduction in 0.5 M H₂SO₄ is studied by cyclic voltammetry. Dependences of voltammogram parameters (currents and potentials of maximums of the Co^3+/2+TMPP redox reaction, numbers of adsorbed and working molecules, values of uncompensated layer resistance) on the adsorbate concentration (10^–6 to 10^–3 M) in chloroform are analyzed. It is concluded that adsorbed molecules change their orientation from a flat to an inclined position at c _CoMPP> 5 × 10^–5 M. The optimum, as to the effectiveness of CoTMPP in the oxygen reduction, is the adsorption layer thickness close to the thickness of a monolayer of flatly-oriented molecules.     

Methane Adsorption and Plasma-Assisted Catalytic Conversion on the Surface of γ-Alumina

Diffuse scattering IR spectroscopy was applied to study the adsorption and plasma-assisted catalytic conversion of methane (deuteromethane) on the surface of -alumina. It was found that CH₄ adsorption sites on the -Al₂O₃ surface were formed by molecular and dissociative mechanisms under the action of an electric-discharge plasma at room temperature. As distinct from -radiolysis, plasma treatment leads to the formation of acetylene in addition to other hydrocarbon products, aluminum hydrides, and surface hydroxyl groups. Plausible mechanisms were proposed for plasma-assisted catalytic reactions in the -Al₂O₃–adsorbed CH₄(CD₄) system.     

Interaction of Chloride Anion and Chlorine Atom with Indium and Gallium Surfaces: A Quantum-chemical Study

The adsorption of the chloride ion and chlorine atom on clusters simulating the surface of the (111) and (001) faces of the crystal lattice of indium and liquid gallium are calculated using the Hartree–Fock–Roothaan and density functional (B3LYP) quantum-chemical methods. The energy of adsorption of chloride ions from a gas phase at these faces increases in the following series: bridgehollow < on-top positions and equals to 179 kJ mol^–1 for In(111) and 183 kJ mol^–1 for gallium in the on-top position. Both metals exhibit similarity in the formation of bonds between their surface atoms and the adsorbate. The adsorbate charge does not depend on the adsorbed form (chloride ion or chlorine atom) and equals 0.5e. Parameter of a virial adsorption isotherm is estimated with allowance for coulombic interactions near the metal/electrolyte interface.     

Estimates of the Catalytic Efficiency of a Heterogeneous Catalyst for Acetylene Hydrochlorination on the Surface of Mechanically Activated K2PtCl6 Salt

Acetylene hydrochlorination by gaseous HCl on the surface of the mechanically activated salt K₂PtCl₆ is shown to occur as a catalytic reaction. Using a modified kinetic distribution method, the specific catalytic activity of the mechanically activated catalyst was found to be equal to 0.2 (mol C₂H₂) (mol Pt)^–1 s^–1.     

Effect of high pressure on the rate constant of the Diels-Alder reaction between furan and maleic anhydride

The effect of high pressure (up to 700 MPa) on the rate of the Diels-Alder reaction between furan and maleic anhydride has been investigated in deuterated acetone at 20C. The volume effect of the reaction at atmospheric pressure is found to be V₀=–28.0 cm³/mole. The rate constants for the formation, decomposition and isomerization of the products have been found by numerical integration. The volume of activation V in the pressure range studied has been determined from the observed dependence of log k upon P by spline approximation and was found to be –30.5 cm³/mole at atmospheric pressure, close to the volume change in the reaction, which is consistent with the assumption of a conjugated cyclic transition state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 525–529, March, 1990.     

Selectivity of liquid-adsorption chromatography on hydroxylated silica gel with nonpolar and polar eluents

Summary The effect of nonpolar (hexane, decane, benzene) and polar (water, isopropanol, water+isopropanol) eluents on separation of aromatic hydrocarbons and their derivatives in liquid-adsorption chromatography on hydroxylated silica gel columns has been studied. The work has revealed that the traditional application areas of hydroxylated silica gel in liquid chromatography may be extended. In particular it has been shown that, first, polar compounds may be separated on hydroxylated silica gel with nonpolar eluents at high temperatures (100–150°C) and that polar and nonpolar compounds may be separated using pure water as eluent. The effect of adsorbed moisture on retention behaviour of silica gel with nonpolar eluents has also been investigated.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.     

A comparative study of trace enrichment of chlorophenols in water by extraction with C6 and C8 alkanes and by C18 reversed-phase adsorption

The efficiency, reproducibility and sensitivity ofn-hexane and iso-octane extraction and of C₁₈ reversed-phase adsorption for accumulation of 4-chloro-, 2,4-dichloro-, 2,4,5- and 2,4,6-trichloro-, 2,3,4,6-tetrachloro- and pentachlorophenol from aqueous solutions were compared. In extraction procedures the acetyl and pentafluorobenzoyl derivatives of chlorophenols were extracted from water. In adsorption procedure chlorophenols adsorbed on a Sep-Pak C₁₈ cartridge were eluted with acetone and after that derivatized analogously.All three procedures were found to be applicable for an efficient trace enrichment of chlorophenols in water, the proper choice being dependent on the required sensitivity of the analysis. Lower detection limits of single compounds at 10 ng·1^–1 levels were achieved by adsorption procedure owing to the more uniform and for most chlorophenols higher adsorption than extraction recoveries as well as owing to the possibility of treating larger volumes of water samples. The extraction procedure could be successfully applied to the concentrations of chlorophenols in water 1g·1^–1.Owing to its higher efficiency and better sensitivity the C₁₈ reversed-phase adsorption procedure was chosen as the more suitable one for the determination of chlorophenol levels in surface, ground and drinking waters. The conversion of chlorophenols accumulated from a water sample parallel to both acetyl and pentafluorobenzoyl derivatives and the analysis of both types of derivatives on two basically different gas Chromatographic columns were recommended for a more reliable identification and quantitation of the compounds analyzed.     

Study of the influence of alkali element compounds on the activity of aluminopalladium catalysts for oxidation of carbon monoxide

A discussion is presented of a discovery that the anionic part of sodium salts introduced into the catalyst by impregnation of -Al₂O₃ after deposition of palladium salts and their reduction in that catalyst affects the activity and dynamic properties of the catalysts in the oxidation reaction of CO into CO₂ at stoichiometric ratios of CO/O₂ = 2.Scientific-Production Association Gos. In-t Prikl. Khim., Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 591–595, September–October, 1991. Original article submitted July 17, 1991.     

Redox reactions of basic fuchsin in homogeneous aqueous media

The pulse-radiolysis technique has been employed to understand the reaction mechanism and to characterize the transient species involved in the redox processes taking place in the radiation chemistry of basic fuchsin (BF⁺). One-electron reduction and oxidation reactions of BF⁺ have been carried out in homogeneous aqueous solutions employing various reducing (e _aq ^– , (CH₃)₂COH, CO ₂ ^– ) and oxidizing (N ₃, Br, Cl ₂ ^– Br ₂ ^– ) radicals. The absorption spectra of the transients formed in the above reactions have been attributed to semi-reduced and semi-oxidized species of BF⁺, respectively. The kinetic and spectroscopic properties of these transients have been evaluated. The reaction with H and OH radicals have also been performed and compared with those of specific one-electron reducing and oxidizing radicals. These reactions have been inferred predominantly by addition to BF⁺. Protolytic equilibria involving semi-reduced species of basic fuchsin have been studied over the pH range from 2 to 10 and the pK _a has been determined to be 3.9.     

Effect of the potential of an external electron donor on C<Subscript>2</Subscript>H<Subscript>2</Subscript> reduction catalyzed by the nitrogenase active center (FeMoco) isolated from the enzyme

The effect of potential value and chemical properties of an external electron donor on C₂H₂ reduction catalyzed by nitrogenase active center (cluster [(₆-N)Fe₇MoS₉·homocitrate] FeMoco isolated from the enzyme) has been investigated in the presence of proton donors of different acidity. The temperature—reaction rate dependences of these reactions have been studied. It has been shown that the rate-limiting steps of the reactions differ depending on the proton donor used. When thiophenol or water are used as proton donors, and electrochemical step — the electron transfer from cathode to adsorbed catalytic cluster — has been found to be a rate-limiting one. The effective activation energy of ethane formation as a product of four-electron C₂H₂ reduction is found to be 1.5 times lower than that of ethylene, namely, 13 kcal mol^–1. When stronger acid, pentafluorothiophenol, is used as a proton donor, the chemical step of intramolecular rearrangement of the catalyst—substrate complex taking place in solution becomes a rate-limiting one. The effective activation energies of both ethylene and ethane become equal to 32 kcal mol^–1.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1583–1591, August, 2004.     

Heterogeneous-catalytic fischer reaction

The catalytic synthesis of 7-azaindole and its 2-methyl derivative has been accomplished for the first time by cyclization of acetaldehyde and acetone 2-pyridylhydrazones in the presence of -Al₂O₃ and fluorinated aluminum oxide. The temperature dependence of the yields of reaction products — azaindoles and 2-aminopyridine — was studied. The cyclization of acetaldehyde 2-pyridylhydrazone proceeds under more severe conditions. The maximum yield of 7-azaindole is 15% at 450° on fluorinated aluminum oxide. The yield of 2-methyl-7-azaindole reaches 50% at 315°. Fluorinated aluminum oxide displays higher catalytic activity.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 656–658, May, 1972.     

Pore structure of “sivol”

Small-angle x-ray scattering has been used in an investigation of the pore structure of sivol, a material prepared by thermochemical treatment of chrysotile asbestos. It has been shown that sivol has a well-developed pore structure. Pore size distribution curves have been obtained, showing a maximum with a radius of gyration R=2.5–3.0 nm. The data from small-angle scattering are in good agreement with results obtained in previous calculations based on adsorption measurements (for R 2.5 nm). It has been shown that some of the finest pores are not accessible for the molecules being adsorbed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 978–981, May, 1990.     

Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO₃)₃ and Cr(NO₃)₃ solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al³⁺ ions in 10^–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al³⁺ adsorption and membrane charge reversal at Al³⁺ concentration in a solution higher than 10^–6 M. The dependences of the ion selectivity on pH and Al³⁺ concentration C _Al in a solution are similar. At pH < 3 and C _Al > 10^–6 M, the _1–2 > _1–1 > _2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the _2–1 > _1–1 > _1–2 series characteristic of positively charged membranes.     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.     

Molecular structure of mixed adsorption layers surfactant—polymer at a liquid—liquid interface

Isotherms of the binding of dodecyl sulfate anions (DDS^–)and Na⁺ counterions during their coadsorption with a nonionic polymer. proxanol (PR). at the interface of dodecane-water emulsions have been measured by conductometry and Na-selective potentiometry. The adsorption of DDS^– and PR is concurrent. The affinity constant of PR to the interface determined by the Langmuir model decreases as the concentration of PR increases, and the surface concentration of DDS^– tends to a nonzero limiting value at high concentrations of PR. The surface (_o) and electrokinetic () potentials at the interface have been determined at various polymer concentrations by the spin probe and electrophoresis methods. The average dielectric permeability and density of polymer segments in We adsorption layer have been determined by ESR. The lower boundary of the hydrodynamic thickness of the polymer adsorption layer at the interface has been estimated from the dependences of _o and on the ionic strength.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1653–1661, July, 1996.     

Kinetics of the periodate oxidation of octacyanomolybdate(IV) in ethanol-water solvent mixtures

The kinetics of the oxidation of Mo(CN) ₈ ^4– by IO ₄ ^– has been studied in ethanol—water solvent mixtures over a temperature range of 15–35 °C. The effect of solvent composition on the reaction rate and the mechanism has been investigated. Activation parameters are given. An inner-sphere mechanism, consistent with the kinetic results, is proposed.

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Kinetik der Periodat-Oxidation von Octacyanomolybdat(IV) in Ethanol-Wasser

Zusammenfassung Die Kinetik der Oxidation von Mo(CN) ₈ ^4– mit IO_4/– wurde in Ethanol—Wasser über einen Temperaturbereich von 15–35 °C untersucht. Der Effekt der Lösungsmittelzusammensetzung auf die Reaktionsgeschwindigkeit und der Mechanismus der Reaktion werden diskutiert. Die Aktivierungsparameter sind angeführt. Es wird ein Inner-Sphere-Mechanismus vorgeschlagen, der mit den kinetischen Ergebnissen konsistent ist.