Effect of Bismuth Additives on the Properties of Vanadium–Phosphorus Oxide Catalyst in the Partial Oxidation of n-Pentane

The selective oxidation of n-pentane on vanadium–phosphorus oxide (VPO) catalysts with bismuth additives (Bi/V = 0–0.30) is studied. The catalysts are characterized by XRD, XPS, and specific surface area measurements using nitrogen adsorption. Their acidic properties are studied (using ammonia TPD and the 2-methyl-3-butyn-2-ol reaction). It was found that the introduction of bismuth insignificantly affects the specific surface area but increases the surface concentration of phosphorus and changes the acidic properties of the catalysts. The specific catalytic activity of samples in n-pentane oxidation correlates with the effective charge of surface oxygen (E _b of O1s electrons). The selectivity to citraconic anhydride increases with an increase in the general surface acidity. The selectivity to maleic anhydride increases with an increase in the Brønsted acidity of the surface. The selectivity to phthalic anhydride increases with an increase in the Lewis acidity. The pathways of product formation in the partial oxidation of n-pentane are proposed.     

Determination of the surface area of supported metallic catalysts by a kinetic method

The possibility of using a kinetic method to determine the surface area of supported platinum and nickel catalysts with a low active-phase surface area is considered. The advantages and drawbacks of the method are discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 125–127, January–February, 1990.     

Reversible and Irreversible Deactivation of Supported Bimetallic Catalysts for the Dehydrogenation of Lower Paraffins

The reasons and nature of the deactivation of spinel-supported bimetallic Pt–Sn, Pt–In, and Pt–Cu catalysts in the steam dehydrogenation of C₄–C₅paraffins are analyzed. The deactivation can be reversible and irreversible. Reversible deactivation is associated with the effects of the composition of reaction medium and gaseous medium for preliminary treatment on the surface composition of supported bimetallic alloys and with the coking of catalysts. Irreversible deactivation can result from the irreproducibility of the phase composition and dispersion of supported alloys in dehydrogenation–regeneration cycles and from the carbon erosion of catalysts. This erosion consists in the removal of active metal particles to the bulk of carbon deposits. The formation of carbon deposits on the surfaces of spinel supports and bimetallic catalysts is considered. Recommendations for optimizing the composition and the operating conditions of catalysts are given in order to reduce the effects of factors that result in reversible and irreversible deactivation.     

Carbon nanostructures as hydrogen sorbent for anode of a chemical power cell

Carbon nanofibers with a porous structure and a specific surface area of 300– 475 m² g¹ were synthesized by pyrolysis of acetylene on iron-containing catalysts. The possibility of using the carbon nanostructures synthesized as hydrogen sorbents to replace hydride-forming metal alloys in chemical power cells was analyzed.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 12, 2004, pp. 1980–1984.Original Russian Text Copyright © 2004 by Danilov, Melezhik.     

Vapor phase oxidation of methylpyridine aldehydes

A study is made of the contact oxidation of -, ß- and -methylpyridines by air, over the temperature range 390°–490° C, contact time 0.17–1.0 sec, mole ratio oxygenmethylpyridine 0.5 to 401, with dilution of the air-vapor mixture with water in the ratio 15–103 mole water per mole methylpyridine, using two vanadium oxide catalysts differing in respect of sizes of specific surface areas.Use of the low specific surface area catalyst increases the selectivity of the process, by diminishing the proportion of secondary reaction products of the aldehydes and decreasing the complete oxidation of the methylpyridines.     

Combustion of Carbon Black Catalyzed by Transition Metal-Promoted Y2O3–CeO2–ZrO2 Solid Solutions1

The activity of M-free and M-loaded 10YO_1.5–10CeO₂–80ZrO₂ solid solution (M = Cu, V, or W) towards carbon black combustion was studied using TG/DTA and TPO techniques. It was demonstrated that all studied catalysts lower the temperature of carbon black combustion. The selectivity of the catalytic reaction in CO₂ formation was 100%. It was evidenced that the fast oxidation of carbon at lower temperatures, observed only in the TG/DTA apparatus, was due to heat- and mass-transfer limitations, resulting in a runaway reaction. Using TPR technique, it was shown that, in the temperature range of DTA curve, oxygen on the catalyst surface was rather reactive (and, therefore, it could be easily released by support for the oxidation of carbon), whereas the reactivity of bulk oxygen was negligible. The activity of the metal-loaded 10YO_1.5–10CeO₂–80ZrO₂ (Y-10) samples varied according to the following sequence: Cu/Y-10 > V/Y-10 > W/Y-10. For Cu- and V-containing catalysts, a contribution of a surface redox mechanism in reaction was proposed by comparing EPR spectra of pure catalysts with those of the samples (catalysts mixed with carbon black) after catalysis.     

Cyclohexanol dehydrogenation over Cu/SiO2 and CuO/SiO2: A comparison

Various CuO/SiO₂ catalysts were prepared and characterized by XRD, surface area and metal area measurements. While dehydrogenation activity for cyclohexanol was observed at 473–573 K on reduced catalysts, it was observed only at 573 K on the unreduced catalyst.IICT Communication No: 3261     

The determination of surface polarity of bismuth-molybdenum oxidation catalysts by gas chromatography

Summary The adsorption of aromatic and aliphatic hydrocarbons was investigated using gas chromatography on Bi₂O₃, MoO₃ and mixed Bi–Mo oxidation catalysts. As a measure of polarity of a catalyst, the difference between the chemical potential of aromatic and aliphatic hydrocarbons at the same surface concentration was used. The chemical potentials were estimated from elution chromatographic data. The data for C₆–C₉ methylbenzenes and C₆–C₁₂ n-alkanes were obtained in the temperature range 60–300°C in nitrogen as a carrier gas. Using air as carrier gas, introduction of water pulses on a catalyst does not change the elution characteristics. The elution of alkenes, alkynes, dienes and carbonyl compounds was disturbed by reaction of these compounds on the surface. The polarity of catalysts decreased in the order mixed Bi–Mo catalysts, MoO₃, Bi₂O₃. The polarities observed are compared with polarities of some other solids and liquids and the role of polarity of the surface in catalytic oxidation reactions is briefly discussed.     

Effect of the Conditions of Thermal Treatment of Molybdenum–Titanium and Vanadium–Molybdenum–Titanium Oxide Catalysts on Pore Structure Formation

The effect of the conditions of thermal treatment on the texture formation in molybdenum–titanium oxide (Mo–Ti–O) and vanadium–molybdenum–titanium oxide (V–Mo–Ti–O) catalysts was studied. It was found that the presence of MoO₃ in the Mo–Ti–O catalyst resulted in the stabilization of the surface area of anatase and in the retention of the fine pore structure upon thermal treatment because of the insertion of highly dispersed molybdenum crystallites into the aggregates of anatase crystallites, preventing from their agglomeration over a wide range of temperatures. In the presence of MoO₃ and V₂O₅ in the catalyst, anatase particles underwent agglomeration as the temperature was increased. This resulted in a more drastic decrease in the specific surface area and an increase in the pore size, as compared with binary samples, because of the formation of a thermally labile vanadium–molybdenum compound at the surface of anatase.     

Conversion of 2-propanol over chromium orthophosphates

The conversion (dehydration/dehydrogenation) of 2-propanol on a series of CrPO₄ (Cr/P=1) catalysts, differently prepared and thermally treated at 773–1073 K, has been studied by microcatalytic pulse reactor technique at different temperatures (473–573 K). Catalytic performance is strongly affected by the precipitation agent. Catalysts obtained in propylene oxide-aqueous ammonia showed the highest activity towards propene compared to other catalysts. Calcination at increasing temperatures caused a decrease in activity due to the decrease in surface acid character. Dehydrogenation to 2-propanone occurs to a small extent at all reaction temperatures. Propene selectivity strongly increases with increasing reaction temperature.     

Kinetics of methylphenylcarbinol dehydration in styrene

Conclusions A study has been made of the kinetics of the dehydration of methylphenylcarbinol in styrene containing aluminum oxide; equations are proposed for describing reaction rates in the kinetic and internal transition regions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 38–43, January, 1978.The authors would like to thank D. Z. Levin who determined the specific surface areas and mean pore radii of the various catalysts.     

Catalytic performance of Fe-modified AlPO4 catalyst in cyclohexene skeletal isomerization

Iron-modified AlPO₄ catalysts (0.5–5 wt.% Fe₂O₃) have been prepared by impregnation until incipient wetness with different iron(III) salts. The resulting solids, after characterization by surface area, XRD and DRIFT measurements, were checked for their surface acidity through their catalytic activity towards cyclohexene skeletal isomerization test reaction. It was found that iron(III) increases the catalytic performance of AlPO₄ and besides, the iron(III) salt used strongly influences the activity. Thus, the catalysts prepared using complexed iron(III) salts as starting materials presented higher specific activity (and hence, acidity) than those prepared using iron(III) nitrate. Moreover, a maximum in activity was found for 2 wt.% Fe₂O₃.     

Mechanism of the interactions of NO with CO on oxide catalysts

The rate of the reduction of nitrogen monoxide by carbon monoxide on transition metal oxides and mixed catalysts based on them and the rates of the individual interactions of the reactants with the catalysts at different extends of reduction of the surface have been studied. These data, as well as the results of an investigation of the adsorbed molecules by IF diffuse reflectance spectroscopy attest to a concerted mechanism of catalysis, which includes a step resulting in the formation of a nitrosyl complex. It has been concluded that catalysts for this reaction must contain complex-forming eléments, which may be oxides of iron, cobalt, and nickel among the oxides and may be rhodium, ruthenium, and palladium among the metals, in their composition.Azerbaidzhan Institute of Petroleum and Chemistry, Baku. Translated from Teoreticheskaya i ÉksperimentaI'naya Khimiya, Vol. 27, No. 5, pp. 567–573, September–October, 1991. Original article submitted July 23, 1991.     

Determination of the rate constants for reactions of gaseous substrates with adsorbed O− radical anions

We consider the possibility of determining the rate constants for reactions of gaseous substrates with O^– radical anions adsorbed on catalysts from the loss of the substrate from the gas phase. We consider two reaction pathways, including attack on O^– by the substrate from the gas phase and from the surface of the contact catalyst, under conditions of equilibrium distribution of the substrate between the phases.L. M. Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, 70 ul. R. Lyuksemburg, Donetsk 340114, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 80–82, March–April 1996. Original article submitted June 6, 1995.     

Desorption of catalytic oxidation products of o-xylene from the surface of carbon catalysts

In a study of the oxidation of o-xylene on carbons (in the range of 523–573°K) under nonstationary conditions, it was found that considerable amounts of the reaction products (phthalic anhydride and CO₂) are adsorbed on the surface of the catalysts (phthalic anhydride more strongly than CO₂). The adsorption of the products is chemical in nature, like the adsorption of initial o-xylene. The bond between the adsorbates and the surface weakens with increase in the number of acidic groups on the surface. Since the active carbons are characterized by a higher basicity than the oxidized ones, in the first case the oxidation products of o-xylene are adsorbed more strongly and desorbed more slowly.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 499–503, July–August, 1986.     

Mechanism of the Effect of Thermal Treatment on the Formation of Strong Acid Sites in the Surface Layers of Sulfated Metal Oxides

Strong acid catalysts were synthesized by the impregnation of hydrated ZrO₂ and TiO₂ with sulfuric acid followed by thermal treatment at different temperatures. The surface acidity and crystallochemical characteristics of the catalysts were studied by potentiometry and X-ray diffraction analysis, respectively. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 350 to 600°C for SO^2– ₄/ZrO₂ or to 200°C for SO^2– ₄/TiO₂; this increase correlated with the degrees of crystallinity of the samples. A hypothesis was proposed to explain the gradual accumulation of acid sites in the surface layer in the course of thermal treatment. It was assumed that, because of crystallographic changes that caused the weakening or even rupture of Zr–O–S and Ti–O–S bonds in modified surface layers, these layers exhibited an enhanced reactivity in contact with water vapor. Subsequently, this resulted in the formation of strongly acidic grafted M–O–SO₃–H⁺ groups.     

Selective alcohol oxidation to aldehydes and ketones over base-promoted gold–palladium clusters as recyclable quasihomogeneous and heterogeneous metal catalysts

Bimetallic gold–palladium clusters, with an average size of 1.9 nm and composed of 80 mol% gold, proved to be highly active and selective metal catalysts for the organic phase oxidation with O₂ of aliphatic, allylic and benzylic alcohols to the corresponding carbonyl products. Polyvinylpyrrolidone stabilized gold–palladium clusters dispersed in N,N-dimethylformamide emerged as promising quasihomogeneous metal catalysts for the oxidation of benzyl alcohol to benzaldehyde with full selectivity; they could be efficiently recycled with unaffected catalytic performance by solvent-resistant nanofiltration. Highly active and durable heterogeneous catalysts for the amide phase or solvent-free alcohol oxidation were prepared by the quantitative immobilization of the optimized gold–palladium clusters on the high surface area basic BaAl₂O₄ spinel support with preservation of the bimetallic clusters’ nanodispersion.     

Decomposition of Chlorinated Hydrocarbons on Iron-Group Metals

The decomposition of 1,2-dichloroethane and chlorobenzene on nickel–alumina, cobalt–alumina, and iron–alumina catalysts at 400–600°C was studied. Thermodynamic calculations demonstrated that the susceptibility of metals to chlorination under exposure to HCl increases in the order Ni < Co < Fe. The addition of hydrogen to the reaction mixture was found to dramatically decrease the rate of carbon deposition in the decomposition of 1,2-dichloroethane because of the intense hydrogenation of intermediates that are graphite precursors. Two fundamentally different reaction paths were found in the degradation of 1,2-dichloroethane: decomposition via a carbide-cycle mechanism with the formation of carbon as the main product (under conditions of a deficiency of hydrogen) and 1,2-dichloroethane hydrodechlorination accompanied by methanation of the formed carbon (under conditions of an excess of hydrogen). The degradation of chlorobenzene diluted with hydrogen in a molar ratio of 1 : 50 was not accompanied by carbon formation on the catalyst. A comparison between the selectivity for reaction products on nickel–alumina and cobalt–alumina catalysts indicated that the former catalyst is more active in the rupture of C–C bonds and in the methanation reaction of deposited carbon, whereas the latter is more favorable for hydrodechlorination. The optimum conditions and thermal regime for efficient and stable operation of the catalysts were found.     

Role of the Surface Acid–Base Properties of Silver Catalysts in the Partial Oxidation of Ethylene Glycol

The acid–base properties of a bulk silver catalyst and silver catalysts supported on various carriers for the partial oxidation of ethylene glycol were studied. A relationship between the catalytic activity and the concentration of surface acid sites in the catalysts was found. A mechanism was proposed for the participation of Lewis acid sites in the reaction of partial ethylene glycol oxidation to glyoxal.     

Influence of the Texture of Woven Materials on Their Etching Rate in Oxygen Plasma

The oxygen glow-discharge plasma treatment of a poly(ethylene terephthalate) film and fabric differing in their specific surface area was studied. The rates of mass loss, oxygen uptake, and gas evolution were measured over the discharge current and pressure ranges 20–110 mA and 50–200 Pa, respectively, at a sample temperature of 357 K. The specific etching and product formation rates calculated with accounting for the total surface area of fabric samples were shown to be not affected by the texture of studied materials.