表面性质对甲烷芳构化Mo基催化剂反应性能的影响

研究了不同载体对Mo基催化剂反应性能的影响，发现对于在无氧条件下的甲烷芳构化反应，分子筛酸性，结构和金属氧化物的存在这3个因素是至关重要的，考察了作为第2组分的Zn,W,Cu,Cr,Ni5种元素对Mo/HZSM-5反应性能的影响，发现第2组分的添加均在不同程度上提高了催化剂的甲烷芳构化活性和选择性，异丙醇分解反应的结果表明，Zn,W,Cu的加入，增加了催化剂的脱氢中心强度，Cr,Ni的加入，增加了催化剂的酸中心强度，酸中心和脱氢中心的加强有利于甲烷芳构化反应。     

Solubility of methane in water and in a medium for the cultivation of methanotrophs bacteria

Solubility of methane in water and in an aqueous growth medium for the cultivation of methanotrophs bacteria was determined over the temperature range 293.15 to 323.15 K and at atmospheric pressure. The measurements were carried out in a Ben-Naim/Baer type apparatus with a precision of about ±0.3%. The experimental results were determined using accurate thermodynamic relations. The mole fractions of the dissolved gas at the gas partial pressure of 101.325 kPa, the Henry coefficients at the water vapour pressure and the Ostwald coefficients at infinite dilution were obtained. A comparison between the solubility of methane in water and those observed in fermentation medium over the temperature range of 298.15 to 308.15 K has shown that this gas is about ±2.3% more soluble in water.The temperature dependence of the mole fractions of methane was also determined using the Clarke-Glew-Weiss equation and the thermodynamic quantities, Gibbs energy, enthalpy and entropy changes, associated with the dissolution process were calculated.Furthermore, the experimental Henry coefficients for methane in water are compared with those calculated by the scaled particle theory. The estimated Henry coefficients are about ±4% lower than the experimental ones.     

Methane oxidative coupling over different alkalidoped catalysts: A comparison of ceramic membrane reactors and conventional fixed bed reactors

Methane oxidative coupling has been carried out over Li/MgO, Li/Sn/MgO, Li/Na/MgO, Li/La/MgO, Na/Sm₂O₃, NaCl/CsCl/MgO and Na/W/Mn/SiO₂ catalysts, using a fixed bed reactor and an inert ceramic membrane reactor in which the membrane acted as an oxygen distributor to the catalytic bed. In most cases, the ceramic membrane reactor provided a significantly higher selectivity than the fixed bed reactor, at the same conversion level.     

Oxidative conversion of methane over MgO/ZSM-5 catalysts with different Si/Al ratios

It is found that the lower the Si/Al ratio of ZSM-5 in the catalytic system MgO/ZSM-5, the higher is the activity and selectivity in the reaction of oxidative conversion of methane. The catalytic properties reflect quite closely the basic properties of the samples, studied by means of temperature-programmed desorption of CO₂.     

Synthesen von Benzofuro[2,3-d]pyrimidin-2,4-dionen

Summary 5-Phenyl-barbituric acids (1) can be cyclized to Benzofuro[2,3-d]pyrimidines (3) either directly by cyclodehydrogenation with palladium-charcoal or via oxidation to 3-hydroxy-3-phenylbarbituric acids (2) and subsequent cyclodehydratation by treatment with strong acids.

Herrn Prof. Dr. H. Junek zur Vollendung seines 60. Lebensjahres gewidmet.     

The counterion influence on the CH-activation of methane by palladium(II) biscarbene complexes - structures, reactivity and DFT calculations

Novel bridged palladium(II) biscarbene complexes with different counterions are reported: 1,1^′-dimethyl-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene palladium(II) bischloride (1) and bis(trifluoroacetate) (2) have been synthesized in good yields. Both complexes are active in the catalytic conversion of methane to methanol and show comparable activities to previously published NHC-catalysts. The results of the single-crystal X-ray structure determination of 1,1^′-dimethyl-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene palladium(II) bischloride (1) and 1,1^′-dimethyl-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene palladium (II) bis(trifluoro-acetate) 2 confirmed the structural similarity to the known corresponding palladium bromide and iodide complexes. Since free 1,1^′-dimethyl-R-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene are only available in low yields these compounds have been synthesized via the bromide complex, exchanging the counterion by AgCF₃COO or by exchanging the counterion of the imidazolium salt by NH₄PF₆.     

Solubility of methane in aqueous solutions of triethylenediamine

The solubilities of methane were measured in water and aqueous solutions of triethylenediamine (TED), triethylenediamine hydrochloride (TED·HCl), and HCl at several concentrations up to 1M at 5° intervals from 5 to 25°C. Methane solubilities in solutions of TED·HCl and HCl are lower than those in water and decrease with increasing cosolute concentration. In contrast, the solubilities in TED solutions are greater than those in water and increase with increasing TED concentration. The order of methane solubilities at 25°C in water and in 0.5M aqueous solutions is TED>H₂O>HCl>TED·HCl with Ostwald coefficients of 3.57×10^–2, 3.44×10^–2, 3.26×10^–2, and 3.19×10^–2, respectively, and with an experimental precision of about ±0.2×10^–3. Thermodynamic functions for the transfer of methane from water to 0.25, 0.50, and 0.75M aqueous solutions have been calculated on the molar concentration scale. The free energies of transfer are compared with previous results for methane in aqueous solutions of tetraalkylammonium halides.     

Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3−δ membranes

Incorporation of gallium into the perovskite lattice of La_0.3Sr_0.7CoO_3– leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La_0.3Sr_0.7Co_0.8Ga_0.2O_3– ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La_0.3Sr_0.7Co_0.8Ga_0.2O_3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O₂) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10^–6 K^–1 at 360–710 K and 27.9×10^–6 K^–1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La_0.3Sr_0.7Co_0.8Ga_0.2O_3– transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O₂) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O₂)=8×10^–10–3×10^–4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La_0.3Sr_0.7Co_0.8Ga_0.2O_3– membranes are, however, kinetically stable under an air/CH₄ gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO₂ concentrations (>90%), indicating a dominant role of complete CH₄ oxidation on the membrane surface.     

Enthalpy of dissociation and hydration number of methane hydrate from the Clapeyron equation

The enthalpies of the reactions in which methane hydrate is dissociated to methane vapor and either (1) water, or (2) ice are determined by a new analysis using the Clapeyron equation. The difference in enthalpies of the two reactions is used to infer the hydration number at the quadruple point where hydrate, ice, liquid water, and methane vapor coexist. By appropriate corrections, the hydration number at points removed from the quadruple point is also determined. The most important feature of the new analysis is the direct use of the Clapeyron equation. The method avoids the use of certain simplifying assumptions that have compromised the accuracy of previous analyses in which the Clausius-Clapeyron equation was used. The analysis takes into account the finite volumes of all phases, the non-ideality of the vapor phase, and the solubility of methane in water. The results show that the enthalpy of dissociation and hydration number are constant within experimental error over the entire (hydrate, liquid, vapor) coexistence region. The results are more accurate than but entirely consistent with almost all previous studies.     

微波场中Co／La2O3催化甲烷部分氧化制合成气

近年来，对甲烷部分氧化制合成气（ＰＯＭ）的研究，一直十分活跃［１～８］．该反应常用的催化剂是负载型贵金属（Ｒｈ）和过渡金属（Ｎｉ和Ｃｏ）．由于贵金属的价格昂贵，因而Ｎｉ和Ｃｏ受到人们的极大重视，但Ｎｉ和Ｃｏ在反应温度较高时，易发生催化剂的挥发流失和烧...