Electron-beam radiolysis of gaseous alkanes under circulation conditions: Gas-to-liquid transformation

The circulating mode of electron-beam irradiation was used for synthesis of the branched liquid hydrocarbons from the gaseous alkane mixtures, including natural gas and the associated petroleum gas. Atmospheric distillation of resulting liquids was characterized by boiling point range from 36 up to 200–230 °C. The average degree of molecular branching in the synthesized liquids was evaluated on the basis of their antiknock characteristics. The octane values of liquids synthesized from natural gaseous mixtures were above 95. The fractional composition and antiknock characteristics of synthesized liquids suggested the prevalence of C₅–C₁₁ isomers with highly branched structures. Fractional and isomeric compositions of the liquid products depended on the gas-phase composition, dose rate, and gas-dynamic conditions in the irradiation area.     

Behavior of acetates of furanosyl fluorides under protolysis conditions in gaseous phase

Conclusions The behavior of acetates of glycofuranosyl fluorides under protolysis conditions in the gaseous phase is mainly determined by the relative configurations of the substituents at C¹ and C⁴ atoms: the cis isomers form the [MH-HF]⁺ ions with higher probability, and the trans isomers, the [MH-AcOH]⁺ ions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2708–2711, December, 1987.     

Influence of the chemical nature of deposited metal ions on their catalytic properties in oxidation of methane by nitrous oxide

The catalytic properties of deposited metal ions in the reaction between methane and nitrous oxide were studied. On the basis of a previously proposed mechanism for the heterogeneous-catalytic reaction, an interpretation was given for the observed activity and selectivity series with respect to the formation of methanol, carbon monoxide and dioxide. The determining factor regulating the catalytic properties in this system is the bond energy of metal ions with the adsorbed oxygen anion radicals O.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 455–461, July–August, 1988.The authors wish to express their gratitude to V. M. Lukyanchuk for providing samples of the catalysts, and to A. N. Korol' for his assistance in carrying out the chromotographic analysis.     

Effect of an oxidant on the nature of bulk defects in Li/CaO and its catalytic activity in the oxidative dimerization of methane

The nature of bulk defects formed in Li/CaO during the oxidative dimerization of methane with O₂ and N₂O as oxidants is studied with the use of ESR. Changing the oxidant from oxygen to nitrogen oxide results in changes in the nature of the bulk defects and the catalytic behavior of Li/CaO.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 599–601, March, 1993.     

Effect of the chemical nature of metal oxide on adhesion to the polyacrylate matrix in filled nanocomposites

The morphology, particle size, and thermochemical properties of the surface of oxides Al₂O₃, NiO, TiO₂, ZnO, and ZrO₂ obtained by the wire electroexplosion method were studied. The nanoparticles are spherical, with a mean diameter of 54–86 nm depending on the nature of the oxide. The hydrophilicity of the surface of metal oxide nanopowders was found to change in the series NiO-ZrO₂-TiO₂-ZnO-Al₂O₃. Nanocomposites with widely varied compositions were obtained from butyl methacrylate copolymer with 5 wt % methacrylic acid and the oxides under study. The enthalpies of dissolution of the composites in chloroform were determined by Calvet calorimetry. The enthalpies of copolymer mixing with oxides were calculated using the thermochemical cycle. The limiting enthalpies of copolymer adhesion to the oxide surface were calculated from the thermochemical data. The limiting adhesion enthalpy was shown to be negative for all oxides under study; these values decreased in magnitude as the surface hydrophilicity increased. The results were analyzed from the viewpoint of balance between the specific and dispersion interactions at the interface.     

Effect of the nature of the support for copper-cerium oxide catalysts on selective oxidation of CO in hydrogen-rich mixtures

We have studied the catalytic properties of copper-cerium oxide catalysts, supported on zirconium, aluminum, titanium, and manganese oxides, in the reaction of selective oxidation of CO in hydrogen-rich mixtures. We have shown that the high activity and selectivity of catalysts supported on zirconium and aluminum oxides is connected with the presence of (in addition to divalent copper) higher amounts of copper in the (+1) oxidation state in the catalysts. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 119–124, March–April, 2006.     

Mechanisms of methane activation and transformation on molybdenum oxide based catalysts

We present a comprehensive survey of different C-H activation pathways over various kinds of active sites of terminal oxygens [=O] and bridge oxygens [-O-] by using Mo3O9 model systems. This allows us to provide some insights into fundamental issues concerning C-H activation by metal oxo species involved in many heterogeneous, homogeneous, and enzymatic processes. We show that H abstraction is the most feasible reaction pathway for the activation of a C-H bond on molybdenum oxides; and that [=O] is more active than [-O-]. Our calculations also suggest that (2+2) can be an alternative if M=O bond possesses a high polarity, while (5+2) can provide another effective pathway if two M=O bonds are in close proximity. Implications for the related heterogeneous, homogeneous, and enzymatic processes are discussed.     

Theoretical study on the reaction of methane and zinc oxide in gas phase

The mechanism of the reaction between CH₄ and ZnO has been studied theoretically at the CCSD(T)//B3LYP/6-311++G(2d,2p) levels. Four possible reaction pathways, yielding three products of syngas, HCHO and CH₃OH, respectively, have been evaluated. All the four pathways are predicted to occur via the formation of CH₄ZnO molecular complex with two H atoms of CH₄ approaching to the Zn end of ZnO. From this complex, the insertion of ZnO into the CH bond of CH₄ might proceed through two concerted manners along with charge transfer process. The pathway corresponding to the production of syngas is energetically feasible, in which the cleavage of CH and ZnH bonds with the formation of H₂ molecule is predicted to be the rate-limiting-step with the energy barrier of 45.4 kcal/mol.     

Thermogravimetric studies on catalytic effect of metal oxide nanoparticles on asphaltene pyrolysis under inert conditions

This study investigated the catalytic effect of NiO, Co₃O₄ and Fe₃O₄ nanoparticles toward asphaltene thermal decomposition (pyrolysis) under inert conditions. Asphaltene adsorbed onto the selected nanoparticles were subjected to thermal decomposition up to 800?°C in a thermogravimetric analyzer. The presence of nanoparticles caused a significant decrease in the asphaltene decomposition temperature and activation energy. Activation energies for the process were calculated using the Ozawa?CFlynn?CWall method. All the selected metal oxide nanoparticles showed high catalytic activity toward asphaltene decomposition in the following order NiO?>?Co₃O₄?>?Fe₃O₄. This study confirms that metal oxide nanoparticles can significantly enhance the thermal decomposition of heavy hydrocarbons, like asphaltenes.     

过渡金属氧化物催化剂上甲烷催化燃烧的研究

与传统燃烧方式相比 ,催化燃烧因具有能量利用率高 ,且基本无污染等突出优点而受到人们的重视。以Ｐｄ为代表的贵金属燃烧催化剂[1] 的研究发展得较为完善 ,但价格昂贵使这类催化剂难以被推向实用。而过渡金属氧化物则价格便宜 ,并且也被认为是很有潜力的燃烧催化剂[2 ] 。但这类催化剂的高温稳定性差 ,活性也远不及贵金属催化剂。为此 ,人们试图使用Ｌａ ,Ｓｒ等作为助剂 ,使其与活性组分生成具有钙钛矿结构的化合物 ;或使用六铝酸盐催化剂[3] 来克服过渡金属氧化物催化剂的缺点。这些方法对过渡金属氧化物催化剂的性能有所改善 ,但催化剂…     

Catalysts for methane transformation in the absence of oxygen, II. Nature of active centers

The activity of supported manganese oxide catalysts doped with copper, chromium and iron oxides in methane to higher hydrocarbons transformation in non-oxidizing atmosphere has been studied. Chromium and iron oxides are more effective promoters than copper oxide. Redox centers of dehydrogenation ability are active in methane transformations.     

Cyclohexane transformations over metal oxide catalysts. 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al₂O₃, Al₂O₃—F, SiO₂, WO₃/ZrO₂, and La₂Î₃/ZrO₂, in cyclohexane ring opening to form n-hexane were studied. The most active catalyst is Rh/Al₂O₃. Cyclohexane hydrogenolysis to n-hexane also occurs over the Pt/Al_;>2O₃ and Pt/La₂Î₃/ZrO₂ catalysts. Ring opening over the Ru catalysts proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts (350—400 °C), but the ruthenium systems are less selective for n-hexane formation than Rh/Al₂O₃ catalysts. The effects of acid-basic properties of the support and the reaction conditions on the activities of the catalytic systems in cyclohexane ring opening was studied.     

Effect of hydrogen on diamond growth from a gaseous phase

Conclusions There is a range of temperatures and pressures in which dilution with hydrogen, a reaction product, will increase the rate of growth on diamond seed crystals from methane and ethane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1252–1256, June, 1978.     

Dehydrocondensation of methane to higher hydrocarbons on bifunctional catalysts in the absence of oxidizing agents in the gas phase

A study was carried out on the effect of the chemical nature of M_xL_y on the activity and selectivity of bifunctional M_xL_y/zeolite catalysts, where M_xL_y are metal-like transition metal compounds, M is a metal atom (Co, Mo, or W), and L is a nonmetal atom (B or Si), in the dehydrocondensation of methane to give higher hydrocarbons in the absence of gas-phase oxidizing agents. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, 252039 Kiev, Ukraine. Translated from éksperimental’naya i Teoreticheskaya Khimiya, Vol. 33, pp. 243–247, July–August, 1997.     

Ethylene oxidation under conditions of the oxidative coupling of methane

Ethylene conversion under conditions of the oxidative coupling of methane has been investigated. In an empty reactor above 740°C, ethylene oxidation occurs at a higher rate and its main product is carbon monoxide. Filling the reactor with an inert material (quartz) or a NaWMn/SiO₂ catalyst leads to a marked decrease in the ethylene conversion rate. Addition of methane to the reaction mixture dramatically slows down ethylene conversion rate and increases the C₃ hydrocarbon content of the reaction products. The kinetics of ethylene oxidation in the presence of methane over the NaWMn/SiO₂ catalyst is reported.     

Effect of metal oxides on the reforming of methane with carbon dioxide

The effect of basic and rare earth metal oxides on the stability of nickel-based catalysts for the CO₂ reforming of CH₄ has been studied. The addition of metal oxides increased the stability of Ni-based catalysts and reversed the values of the reaction orders with respect to both CH₄ and CO₂. In the presence of metal oxides, the values of the reaction orders with respect to CO₂ partial pressure followed the same trend of catalyst stability.