Oxidative Dimerization Of Methane Research Articles

Oxidative dimerization of methane over CaO doped with chlorides or alkaline metals

Oxidative dimerization of methane has been examined on CaO modified by chlorides or alkaline metals. It has been established that the formation of C 2-hydrocarbons over CaO-CaCl 2 catalysts involves the participation of atomic chlorine generated by the catalyst surface. It has been suggested that the reaction over Na/CaO and Li/CaO catalysts is initiated by atomic oxygen. The reactions schemes for different catalysts are suggested.

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.

Oxidative coupling of methane over alkali-doped antimony oxide

The oxidative dimerization of methane was studied over alkali-doped antimony oxide catalysts. Selectivities for C 2 hydrocarbons as high as 68% were achieved over 5% lithium-doped antimony oxide supported on SiO 2. The addition of small amounts of alkali to supported antimony oxide was found to improve the selectivity for coupled products. However, the nature of the alkali (Li, K, or Cs) made little difference in the final catalytic properties. This increased selectivity is attributed to the scavenging, by the alkali species, of acidic sites on the support, which are believed to be total oxidation sites.

ChemInform Abstract: Oxidative Dimerization of Methane Over Sodium‐Promoted Calcium Oxide.

Abstract Sodium-promoted calcium oxides are active and selective catalysts for the partial oxidation of methane to ethane and ethylene using molecular oxygen as an oxidant. In a conventional fixed-bed flow reactor, operating at atmospheric pressure, a 45% C 2 (sum of ethane and ethylene) selectivity was achieved at a 33% methane conversion over 2.0 g of 15 wt% Na CaO catalyst at 725 °C with a gas mixture of CH 4 O 2 = 2 . The other products were CO, CO 2 , and H 2 . EPR results indicated that [Na + O − ] centers in Na CaO are responsible for the catalytic production of CH 3 · from methane via hydrogen atom abstraction. These CH 3 · radicals dimerize, primarily in the gas phase, to form C 2 H 6 , which further oxidizes to C 2 H 4 . Increasing temperatures reverse the gas-phase equilibrium CH 3 · + O 2 ⇄ CH 3 O 2 · to produce more CH 3 · and increase the C 2 selectivity. The CH 3 O 2 · eventually is converted to carbon oxides under the reaction conditions employed; therefore, increasing O 2 pressures decrease the C 2 selectivity. There is evidence that CH 3 O 2 · in the presence of C 2 H 6 initiates a chain reaction that enhances the methane conversion. The addition of Na + to CaO also reduces the surface area of the catalysts, thus minimizing a nonselective oxidation pathway via surface methoxide intermediates.

Oxidative Coupling of Methane to Higher Hydrocarbons

Abstract Natural gas is an abundant resource in various parts of the world. Methane is the major component of natural gas, often comprising over 90 mol% of the hydrocarbon fraction of the gas. Methane itself is primarily used as a fuel, while the nonmethane components can be separated and used as feedstocks for the production of chemicals or liquid fuels. In many cases, however, natural gas reserves are found in locations distant from their place of utilization. Since it is not generally economical to transport liquefied natural gas, efficient methods are needed to convert methane into transportable liquid products. A possible route is oxidative dimerization of methane followed by oligomer-ization of the C2 products.

Oxidative dimerization of methane over lead-magnesium mixed oxide catalysts

While both methane combustion and methane ammoxidation to HCN over metal catalysts are well known, selective dimerization of methane in the presence of oxygen over oxide catalysts has been achieved only recently. We report results of the oxidative coupling of methane to form ethane and ethylene over a mixed PbO-MgO catalyst. Selectivity for methane conversion to higher hydrocarbons rises to over 80% as reactor temperature is raised to about 800°C over these catalysts when oxygen/methane in the feed is limited. However, selectivity declines as oxygen partial pressure is increased. Both observations are consistent with recently published results for other catalysts containing PbO. Here, optimal reaction conditions give yields of nearly 20%. The PbO-MgO catalyst operates effectively both with and without co-fed oxygen. Productivity, an important consideration for practical processes, was found to be about forty times higher when oxygen is co-fed. The rate of oxygen disappearance over PbO-MgO had a 2 3 order dependence on oxygen pressure under conditions where selectivity was high, indicating that oxygen activation has an important role in the coupling mechanism.

Oxidative dimerization of methane over sodium-promoted calcium oxide

Sodium-promoted calcium oxides are active and selective catalysts for the partial oxidation of methane to ethane and ethylene using molecular oxygen as an oxidant. In a conventional fixed-bed flow reactor, operating at atmospheric pressure, a 45% C 2 (sum of ethane and ethylene) selectivity was achieved at a 33% methane conversion over 2.0 g of 15 wt% Na CaO catalyst at 725 °C with a gas mixture of CH 4 O 2 = 2 . The other products were CO, CO 2, and H 2. EPR results indicated that [Na +O −] centers in Na CaO are responsible for the catalytic production of CH 3· from methane via hydrogen atom abstraction. These CH 3· radicals dimerize, primarily in the gas phase, to form C 2H 6, which further oxidizes to C 2H 4. Increasing temperatures reverse the gas-phase equilibrium CH 3· + O 2 ⇄ CH 3O 2· to produce more CH 3· and increase the C 2 selectivity. The CH 3O 2· eventually is converted to carbon oxides under the reaction conditions employed; therefore, increasing O 2 pressures decrease the C 2 selectivity. There is evidence that CH 3O 2· in the presence of C 2H 6 initiates a chain reaction that enhances the methane conversion. The addition of Na + to CaO also reduces the surface area of the catalysts, thus minimizing a nonselective oxidation pathway via surface methoxide intermediates.

ChemInform Abstract: Oxidative Dimerization of Methane Over Magnesium and Calcium Oxide Catalysts Promoted with Group IA Ions: The Role of (M+O‐) Centers.

AbstractThe oxidative dimerization of CH4 to CH2=CH2 and CH3‐CH3 over MgO and CaO is strongly influenced by certain group IA ions.

Effect of defect structure on the catalytic activity of magnesium oxide in the oxidative dimerization of methane

Effect of defect structure on the catalytic activity of magnesium oxide in the oxidative dimerization of methane

Oxidative dimerization of methane over magnesium and calcium oxide catalysts promoted with Group IA ions: the role of [M+O-] centers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxidative dimerization of methane over magnesium and calcium oxide catalysts promoted with Group IA ions: the role of [M+O-] centersChiu Hsun Lin, Tomoyasu Ito, Jixiang Wang, and Jack H. LunsfordCite this: J. Am. Chem. Soc. 1987, 109, 16, 4808–4810Publication Date (Print):August 1, 1987Publication History Published online1 May 2002Published inissue 1 August 1987https://doi.org/10.1021/ja00250a009RIGHTS & PERMISSIONSArticle Views320Altmetric-Citations105LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (356 KB) Get e-Alerts Get e-Alerts

Contribution of one-electron acceptor centers to oxidative dimerization of methane

The ESR method was used to identify paramagnetic centers in the Pb−Mg oxide system and to study its catalytic properties in oxidative dimerization of methane. Reaction rate is shown to correlate well with the presence of one-electron acceptor centers in the sample.

Activation of hydrocarbons in the oxidative dimerization of methane over alkaline earth metals

Oxidative dimerization of methane over alkaline earth metal oxides and phosphates has been studied. The ratedetermining step is heterolytic C−H bond dissociation of methane on surface basic sites of the catalysts.

ChemInform Abstract: Oxidative Dimerization of Methane over BaCO3, SrCO3 and these Catalysts Promoted with Alkali.

The yield and selectivity for formation of C2hydrocarbons from CH4 and O2 were 18.2 and 48.4% respectively over 2 g of BaCO3 at 1073 K at a CH4 :O2 ratio of 2.0:1, whereas the yield and selectivity were 2.5 and 99.5% over SrCO3 at 973 K at a CH4:O2 ratio of 37.9 : 1.

ChemInform Abstract: Oxidative Dimerization of Methane over Promoted Magnesium Oxide Catalysts. Important Factors.

Various metal doped MgO samples were examined as catalysts for the conversion of methane to ethane and ethylene. Of these, 15 mol% Na+–MgO was found to show the highest C2 hydrocarbon yield (22.4%) with a C2 selectivity of 57% at 1073 K at a CH4/O2 ratio of 2.0.

Oxidative dimerization of methane over cerium mixed oxides and its relation with their ion-conducting characteristics

Selectivities for ethene and ethane formation during oxidative dimerization of methane over cerium mixed oxide catalysts Ce1 –x Ybx02 – 0.5x and SrCe1 –x YbxO3 – 0.5 x appear to be related to the nature of their ionic conduction, decreasing with oxygen ion mobility while increasing with proton mobility.

Importance of the specific surface area of the catalyst in oxidative dimerization of methane over promoted magnesium oxide

A low specific surface area was found to be the key factor for catalytic conversion of methane into ethane and ethylene over various metal-doped MgO catalysts, a result which could be important for other catalyst systems.

Oxidative Dimerization of Methane over Promoted Magnesium Oxide Catalysts. Important Factors

Abstract Various metal doped MgO samples were examined as catalysts for the conversion of methane to ethane and ethylene. Of these, 15 mol% Na+–MgO was found to show the highest C2 hydrocarbon yield (22.4%) with a C2 selectivity of 57% at 1073 K at a CH4/O2 ratio of 2.0.

Oxidative dimerization of methane over lanthanum oxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxidative dimerization of methane over lanthanum oxideChiu Hsun Lin, Kenneth D. Campbell, Ji Xiang Wang, and Jack H. LunsfordCite this: J. Phys. Chem. 1986, 90, 4, 534–537Publication Date (Print):February 1, 1986Publication History Published online1 May 2002Published inissue 1 February 1986https://doi.org/10.1021/j100276a004RIGHTS & PERMISSIONSArticle Views596Altmetric-Citations208LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (485 KB) Get e-Alerts

Oxidative dimerization of methane over a lithium-promoted magnesium oxide catalyst

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxidative dimerization of methane over a lithium-promoted magnesium oxide catalystTomoyasu Ito, Jixiang Wang, Chiu Hsun Lin, and Jack H. LunsfordCite this: J. Am. Chem. Soc. 1985, 107, 18, 5062–5068Publication Date (Print):September 1, 1985Publication History Published online1 May 2002Published inissue 1 September 1985https://doi.org/10.1021/ja00304a008RIGHTS & PERMISSIONSArticle Views1907Altmetric-Citations671LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (875 KB) Get e-Alerts Get e-Alerts