C2 Yield Research Articles

Oxidative coupling of methane over BaF2-TiO2 catalysts

The addition of F− to Ba-Ti mixed oxide catalysts significantly improves the catalytic performances for the oxidative coupling of methane (MOC), which can achieve high C2 yields at wide feed composition range and high GHSV. The effect is particularly marked for the BaF2− TiO2 catalysts containing more than 50 mol% BaF2. The C2 yield of 17% and the C2 selectivity of > 60% were achieved over these catalysts at 700 ° C. After being on stream for 31 h, the ≥ 50 mol% BaF2-TiO2 catalysts showed only a 1–1.5% decrease in the C2 yields. Results obtained by XRD show that various Ba-Ti oxyfluoride phases were formed due to the substitution of F− to O2−.

Oxidative Coupling of Methane over Alkali-Metal-Compound-Promoted Zirconia Catalysts

Upon promoting ZrO2 with alkali metal compounds (chlorides, nitrates, carbonates, or acetates), effective catalytic systems are obtained which are more active, selective, and stable with time-onstream than unpromoted ZrO2 or unsupported promoter compounds at 750°C, PCH4 = 243.2 Torr, CH4/O2 = 4, and a space velocity of 7500 cm3 g−1 h−1. The performance of the catalysts is found to strongly depend on the nature of the alkali salt, the promoter content, the method of catalyst preparation, and the reaction conditions (temperature, partial pressures. CH4/O2 ratio, and contact time). The most effective catalytic system is obtained with Na+-ZrO2-Cl− prepared via the sol-gel method, which leads to a methane conversion of 13.8 mol%, total C2 selectivity of 77 mol% (C2 yield 10.6%), and an ethylene-to-ethane ratio of 3.3 for at least 30 h under the aforementioned conditions and atmospheric pressure. Addition of carbon tetrachloride as a source of chlorine species to the feedstream improves the performance of the catalyst and its stability with time-on-stream. In the latter case, a CH4 conversion of 22.0% and a C2 yield of 17.5% with a C2H4/C2H6 molar ratio of 2.7 are obtained at a space velocity of 3750 cm3 g−1 h−1. In contrast, Na+-ZrO2-Cl− prepared via impregnation, gel-precipitation, physical mixing, or ion-exchange, and the Li-, K-, Rb-, or CsCl-promoted ZrO2 catalysts prepared by any of the above methods, were less effective, even upon the addition of carbon tetrachloride to the feedstream. The relatively high performance of Na+-ZrO2-Cl− (sol-gel) is attributed to the incorporation of Na+Cl− into the ZrO2 matrix, the exposure of an appreciable amount of Na+ and Cl− on the surface, and the increase in basicity and base strength. The relationship between the catalytic performance and the physico-chemical characteristics of the catalysts revealed by XRD, XPS, and basicity (stepwise thermal desorption of CO2) measurements is explored.

Oxidative coupling of methane on lithium-calcium phosphate catalysts

Abstract The oxidative coupling of methane has been tested over a series of lithium-calcium phosphate catalysts at 700 and 775°C with and without the introduction of a small quantity of tetrachloromethane (TCM ) to the feedstream. The selectivity to C2 and higher hydrocarbons and that to oxidation products have been shown to have a dependence on the cation/cation and cation/anion ratio. The highest yield of C2+ hydrocarbons has been obtained on the lithium phosphate catalyst at 775°C but the activity of this catalyst decreased rapidly at this temperature. In contrast, the lithium-calcium phosphate (Li:Ca:P=4:1:2) has shown almost the same activity as the lithium phosphate catalysts while remaining stable at the same temperature for more than 10 h. The effect of the addition of TCM on the selectivity was dependent both on the nature of the catalyst employed as well as the reaction temperature. On lithium doped calcium phosphate catalysts the conversion of methane was enhanced by the introduction of TCM but the selectivity to C2 hydrocarbons was not changed while with the lithium-calcium phosphate catalysts the conversion of methane was suppressed by the presence of TCM.

Synergistic effect of bialkali metal chlorides promoted magnesia on oxidative coupling of methane

Upon promoting MgO (prepared via a sol-gel process) with any binary mixture of the alkali metal chlorides, catalytic systems are obtained which are more active, selective and much more stable with time-on-stream than the respective monoalkali promoted MgO in the oxidative coupling of methane (OCM) to C2 hydrocarbons. The best catalytic performance is obtained over (5 mol% NaCl+5 mol% CsCl)/MgO, which exhibits a C2 yield of 19.7% compared to 5.9 and 4.1% over 10 mol% NaCl/MgO and 10 mol% CsCl/MgO, respectively, at atmospheric pressure, a temperature of 750 °C, a space velocity of 15000 cm3 g−1 h−1,\(P_{CH_4 }\) = 608 Torr and CH4/O2 = 4. A series of different combinations among the five alkali chlorides were made and the afore-mentioned synergistic effect was always observed. The basicity and base strength distribution of the bialkali chloride systems (measured by the gaseous acid adsorption or benzoic acid titration methods) are significantly higher than those of the respective monoalkali halide systems. The relationship between the catalytic performance and basicity/base strength distribution is explored.

Synthese, Struktur und Reaktionen Phenylethinyl‐substituierter Bicyclo[3.3.0]octane

Syntheses, Structures, and Reactions of Phenylethynyl-Substituted Bicyclo[3.3.0]octanes[1] The bicyclo[3.3.0]octane-3,7-dione 5 adds phenylethynyl-cerium(III) dichloride to afford an almost quantitative yield of the 3,7-diols exo,exo-, exo,endo-, and endo,endo-6 (1:2:2) which are separated by flash chromatography. While both exo,endo- and endo,endo-6 are dehydrated by sulfuric acid in acetic acid to furnish the isomeric dienes C2- and Cs-7, exo,exo-6 rearranges to a bicyclic ketone (8), two tricyclic ketones (10a, b), and a tetracyclic ketone (12) as a consequence of the proximity of the endo-phenylethynyl groups. The rearrangements of exo,exo-6 are avoided when chlorotrimethylsilane is used as the dehydrating agent. Thus, a 90% yield of C2- and Cs-7 is realized from the mixture of the 3,7-diols 6. – The 2,6-dione 13 reacts with phenylethynylcerium(III) dichloride to yield the hydroxyketone endo-14 and the 2,6-diols exo,endo- and endo,endo-16 (1:1:3) which are separated by cyclic medium-pressure liquid chromatography. Dehydration of endo-14 furnishes the enone 15 which adds phenylethynylcerium(III) dichloride to afford the endo alcohol 17. Eventually, this is dehydrated to the diene 18. Formation of 18 from exo,endo-16, and endo,endo-16 as well, is accompanied by dehydrating cyclization to the oxanortwistane 19 (20%) readily separated from 18 by chromatography. – The encumbered diphenyldione 20 is converted into the highly substituted bicyclo[3.3.0]octa-2,6-diene 24 in 68% overall yield in a four-step sequence involving additions of phenylethinyl-cerium(III) dichloride (20→21 and 22→23) followed by dehydration of the endo alcohols 21 (→22) and 23 (→24). – In contrast to 20, the dicyanodiketone 25 adds phenylethynylcerium(III) dichloride at both carbonyl groups and, surprisingly, from the endo face, thus affording the exo,exo-diol 26. At 150°C, 26 undergoes quantitatively an intramolecular dehydro Diels-Alder reaction to yield the 1-phenylnaphthalene derivative. 30. The lack of incorporation of deuterium from deuterated solvents attests to the intramolecular nature of the 1,5-hydrogen shift converting the intermediate six-membered cyclic cumulene 29 to the final product 30. – Dehydration of 26 produces the highly substituted bicyclo[3.3.0]octadiene-2,6-dicarbonitrile 27 which rearranges into an equilibrium mixture of the diastereomeric bisallenes exo,exo-, exo,endo-, and endo,endo-28 on treatment with a strong base. In the same way, the identical mixture of diastereomers is obtained from each of the bisallenes 28 which had been separated by preparative medium-pressure liquid chromatography. – The gross structures of all new compounds are based on spectroscopic evidence including IR, NMR, and mass spectra. The structures of endo,endo-6, 12, exo-14, endo,endo-16 (α- and β-form), 19, 24, 26 · 2 Me2SO, 27, exo,exo-28, and endo,endo-28 are established by X-ray diffraction analyses. The preferred conformations of exo-14, endo,endo-16 (α- and β-form), and 26 · 2 Me2SO in the crystalline state, as well as the stereochemistry of the nucleophilic attack to bicyclo[3.3.0]octanediones, and the mechanisms of the intramolecular reactions between the phenylethynyl groups are discussed.

Oxidative Coupling of Methane over Various Barium Salts Mixed with CaO: The Relation with Their Surface Basicities

Abstract Oxidative coupling of methane to ethane and ethylene was carried out over barium salts mixed with CaO catalysts prepared by a wet-mixing method. The mixing effect of the barium salts on the C2 yield at 800 °C was remarkable in the following order: BaBr2 > BaCl2 >> BaI2, Ba(OH)2, BaF2 > BaC2O4, Ba(NO3)2 > BaCO3, BaSO4 > Ba3(PO4)2( > CaO). The high C2 yield of the BaCl2/CaO catalysts was kept relatively long, and was nearly constant (19–20%) over a range of 5 to 30 mol% BaCl2. Measurements of the temperature-programmed desorption of the used barium salt/CaO catalysts showed that a catalyst with the high C2 selectivity and high C2 yield tended to have large CO2 desorption peaks at higher temperatures; they were also well-dispersed with barium ions. In the case of BaCl2/CaO catalysts (2.5–40 mol% BaCl2), a large desorption peak of CO2 was observed at around 730 °C, that was associated with their high C2 yields. The role of basic sites resulting from the desorption of CO2 is discussed.

Catalytic oxidative coupling of methane and surface potential measurements over pure samarium oxide: evidence for a heterogeneous C2 yield limitation

The oxidative coupling of methane has been studied over a pure samarium oxide catalyst by classical tests and surface potential measurements. This latter technique provides some interesting information on the nature of the oxygen species adsorbed over the catalytic surface and on the kinetic parameters of the reactions which take place on the solid. In our experimental conditions (PCH4/PO2= 2) the negatively adsorbed oxygen species involved in the catalytic process is O– below 400°C and O2– at higher temperature. The reactivities of the hydrocarbons follow the order C2 methane, whatever the temperature. The activation energy obtained from classical tests (95 kJ mol–1) is very close to that obtained from surface-potential experiments. The results lead us to propose that an important part of the C2 yield limitation is due to the heterogeneous process.

Oxidative coupling of methane over SrCO3 and SrO

The oxidative coupling of methane has been studied with an SrCO3–SrO mixed catalyst. Two surface states (an SrO-rich surface and an SrCO3-rich surface) were prepared and examined by various methods including XPS. SrO-rich surfaces, prepared by H2 treatment of SrCO3, had a high C2 yield, and evolved CO2 was absorbed by the catalyst at 1023 K. The bulk diffusion of CO2 was considered to be rapid enough to absorb most of the evolved CO2 and to keep SrO partly on the surface (SrCO3-rich surface) at 1023 K. SrCO3-rich surfaces gave low C2 yields, and the surface was composed of both oxides and carbonates. The active sites were considered to be oxides. The SrO surface was more active than MgO in this reaction. However, it was less active under the steady state because of carbonate formation.

Importance of Apparent Density of BaLa2O4 Catalysts in Oxidative Coupling of Methane

Abstract A voluminous catalyst composed of mainly a composite oxide of BaLa2O4 was found to be effective for oxidative coupling of methane to ethane and ethylene. The high C2 yield is probably due to the low apparent density of the catalyst as well as to its high basicity.

Oxidative coupling of methane over CaO catalysts promoted with alkali and alkaline earth oxides

CaO catalysts promoted with various elements were examined systematically for the oxidative coupling of methane. 10 mol% Li+-CaO and 10 mol% Ba2+-CaO gave high C2 yield (23 to 26% at 1023 to 1073 K for 10% Li+-CaO) under CH4 and O2 partial pressure of 2.8 and 1.4 kPa respectively. A three components catalyst, 10 mol% Li+-5 mol% Ba2+-CaO, was also found to be an effective catalyst, given that the reaction temperature to give the maximum C2 yield was lower than those for the two components catalysts under the same reaction condition. Quenching the flow down stream the reactor improved C2 yield.

Oxidative dimerization of methane over well defined lithium-promoted magnesium oxide catalysts

Pure MgO samples having greatly different morphologies and lithium-promoted catalysts derived from these materials have been examined by electron microscopy. In addition, their ability to generate and react with gas-phase methyl radicals has been determined using e.s.r. in combination with a matrix-isolation technique. Lithium caused the MgO to sinter severely at 700 °C, but the resulting material showed improved activity for the generation of methyl radicals. These factors gave rise to catalysts which were moderately active and selective for the oxidative dimerization of CH4 at 700 °C (up to 20% conversion, 66% C2+ selectivity). The results are particularly significant in that catalysts which had been prepared such that the lithium was initially present as Li2O on the surface exhibited almost constant C2+ production as the Li2O was converted to Li2CO3. Thus, neither Li2O nor Li2CO3 is the active phase for the selective conversion of CH4. A catalyst prepared from Li2CO3 and MgO sintered much less extensively, produced more CH3˙ radicals and gave higher yields of C2+ hydrocarbons. A comparison of these catalytic properties suggests that surface area and related morphological factors do not have an adverse effect on the oxidative dimerization reaction, provided the surface can be rendered inert to secondary reactions with methyl radicals.

Citrate utilization by free and immobilized Streptococcus lactis subsp. diacetylactis in continuous culture

The effects of pH, temperature and concentration of citrate were investigated to achieve an optimal production of diacetyl, acetoin and C2 compounds such as acetaldehyde, acetate and ethanol for free and immobilized cells. The critical conditions of culture, 22°C, pH 4.8, increased the production of C4 compounds (diacetyl, acetoin, 2, 3 butylene glycol), C2 compounds (acetaldehyde, ethanol, acetate) and formate. A higher yield of C2 and C4 compounds was observed for the immobilized cells than for the free cells in continuous culture. At 75 mMol/l of citrate, the citrate bioconversion yield was 42.8% and 80% for free and immobilized cells, respectively. This paper discusses citrate and lactose utilization and NADH2 part on diacetyl reduction.

The effects of catalyst surface heterogeneity on the fischer‐tropsch synthesis

AbstractWe find that the surface energetic heterogeneity of Fischer‐Tropsch catalysts is either not important kinetically or may be masked by the effect of increasing molecular size, so that the classical Anderson‐Schulz‐Flory distribution is routinely observed in product distributions. The anomalous yields of C1 and C2 observed in many cases may also be due to surface heterogeneity but can in practice be readily, and more conveniently, accounted for by assigning individual rate constants to their formation.The “break” sometimes observed in ASF distributions cannot be explained by surface heterogeneity and is best explained by the presence of two distinct modes of product formation.

Phosphorus modification of supported Pt catalysts for carbon monoxide hydrogenation

Modifying effect of phosphorus on the catalytic activity of supported Pt and Pt−Fe catalysts for CO hydrogenation has been studied. Phosphorus-containing compounds decrease significantly the methane yield with increasing yield of C2−C7 hydrocarbons.

Estimation of C2 and C3 hydrocarbon production yields of graphite due to hydrogen ion bombardment

A numerical method is proposed for estimating the production yields of C2 and C3 hydrocarbons, which are generated by bombarding graphite with hydrogen ions, from signal intensities of a quadrupole mass spectrometer (QMS). It is shown that the C2H2, C2H4, C2H6, C3H4, C3H6, and C3H8 production yields can be easily estimated by fitting the calculated intensities of QMS signals, by means of summing up the crackings of species, to the measured ones, whose masses range between 24 and 44. The derived formulas can uniquely determine the yields, using the measured data of the cracking coefficients and sensitivities of purified standard gases for the QMS as well as of the intensities of QMS signals.

Multiple-photon dissociation of CH2CO, C2H4 and C4H6O3, fluence dependence of the production of CH2(ã) and C2(a)

Ketene and ethylene have been dissociated with radiation from a TEA CO2 laser at pressures between 1 and 15 mTorr. Laser-induced fluorescence was utilized to make relative concentration measurements of CH2(ã 1A1) and C2(a 3Hu) yields (in the case of ketene) and of C2(a 3Hu) yield (in the case of ethylene) at fluences between 1 and 100 J/cm2. The ketene dissociation was investigated at two different CO2 frequencies corresponding to excitation in different normal modes. By the dissociation of acetic anhydride, CH2(ã 1A1) is produced very efficiently.

Electron Transfer and Ion—Atom Interchange in C+–CO Collisions

Kinetic-energy distributions of CO+ and C2+ ions resulting from C+–CO collisions were measured over the incident ion kinetic-energy range 13–30 eV. These distributions were used for calculation of the reaction energetics. The CO+ kinetic-energy distributions provide strong evidence that this product is formed by both electron transfer and ion—atom interchange. In addition to the major (forward scattered) peak in the C2+ distribution small yields of C2+ were detected at 180° in the center-of-mass system.