Methane Oxidation Over Dual Redox Catalysts. Quarterly Technical Progress Report, April--June 1989 PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Methane Oxidation Over Dual Redox Catalysts. Quarterly Technical Progress Report, April--June 1989 PDF full book. Access full book title Methane Oxidation Over Dual Redox Catalysts. Quarterly Technical Progress Report, April--June 1989 by . Download full books in PDF and EPUB format.
Author: Publisher: ISBN: Category : Languages : en Pages : 19
Book Description
The objective of this research is to develop the scientific background for direct catalytic oxidation of methane over oxides that are doubly doped with transition metal ions. The desired process aims at employing of a double redox mechanism, where one redox couple is utilized for activation of oxygen and another for the conversion of CH3 radicals to carbocations via electron transfer reaction. The latter species can react with surface OH− groups to form methanol or formaldehyde. To establish the foundations for such a process, two groups of the catalysts, one containing dispersed redox centers (Cu{sup I}/Fe{sup III}/ZnO and Cu{sup I}/Sn{sup IV}/ZnO) and a second of delafossite-type oxides containing concentrated redox centers (CuFeO2, CuCoO2) were synthesized and chemically analyzed for composition. For the sake of comparison, undoped ZnO treated in the same way as doped zinc oxide catalysts was also prepared. The samples were characterized by X-ray diffraction, BET surface area measurements and preliminarily by scanning electron microscopy. A catalytic testing unit and reactor to study the title reaction were designed and constructed.
Author: Publisher: ISBN: Category : Languages : en Pages : 19
Book Description
The objective of this research is to develop the scientific background for direct catalytic oxidation of methane over oxides that are doubly doped with transition metal ions. The desired process aims at employing of a double redox mechanism, where one redox couple is utilized for activation of oxygen and another for the conversion of CH3 radicals to carbocations via electron transfer reaction. The latter species can react with surface OH− groups to form methanol or formaldehyde. To establish the foundations for such a process, two groups of the catalysts, one containing dispersed redox centers (Cu{sup I}/Fe{sup III}/ZnO and Cu{sup I}/Sn{sup IV}/ZnO) and a second of delafossite-type oxides containing concentrated redox centers (CuFeO2, CuCoO2) were synthesized and chemically analyzed for composition. For the sake of comparison, undoped ZnO treated in the same way as doped zinc oxide catalysts was also prepared. The samples were characterized by X-ray diffraction, BET surface area measurements and preliminarily by scanning electron microscopy. A catalytic testing unit and reactor to study the title reaction were designed and constructed.
Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
Review and analysis of the literature data on electron transfer itself and electron transfer oxidation of alkyl radicals was done in order to understand the mechanism by which methyl radical can be oxidized to CH3 and further substituted by OH− to form methanol. This allowed to compare and classify the various possible reaction patterns, understand the mechanism and circumstances of operation of each of them and select those which can be involved in oxidation of methyl radical. As a result an approach that is complementary to catalytic test studies was proposed. It consists of investigation of a set of partial reactions which reproduce a whole catalytic cycle in order to prove the reaction mechanism. Synthesis of new oxide catalysts of the delafossite type, containing concentrated double redox sites, were designed. Synthesis of hydrozincite as a starting material for the preparation of doubly doped zinc oxide was performed.
Author: Publisher: ISBN: Category : Languages : en Pages : 18
Book Description
The objective of this research is to develop approaches to direct catalytic oxidation of methane over oxides that are doubly doped with transition metal ions. The desired process aims at employing a double redox mechanism, where one redox couple is utilized for activation of oxygen and another for the trapping of CH3 radicals. The methyl radicals can either recombine, giving C2 hydrocarbons, or be converted, via electron transfer reaction, to carbocations. The latter species can react with surface OH− groups to form methanol or formaldehyde. To choose from several possible catalytic systems, this research initially involved the characterization of the micromorphology and crystalline dimensions of zinc oxide catalysts doped with Cu, Fe, and Sn by scanning electron microscopy. In addition, the determination of surface composition and oxidation states by X-ray photoelectron spectroscopy was carried out. A newly constructed high temperature catalytic testing system has been calibrated (flow meters and temperature controllers), tested for possible gas leaks and integrated with a gas chromatographic analytical unit. A preliminary catalytic test study over a Cu/Fe/ZnO sample was performed. The following products of the methane coupling reaction was found: C2H6, C2H4 and H2O together with CO2. The maximum space time yield of 14 mmol C2 hydrocarbons/g cat/h was obtained at 848°C.
Author: Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
The effect of doping lanthana-based catalysts with antimony and bismuth on the catalytic behavior toward the selective oxidation of methane has been studied. New catalytic results have been obtained upon doping the Sr/La2O3 catalyst, obtained from AMOCO Oil Co., with the acidic Sb and Fe dopants. Both activity and selectivity of the original Sr/La2O3 catalyst can be modified by introducing small amounts of either dopant. Iron doping lowered selectivity to C2 products whereas antimony increased the selectivity while decreasing the reaction temperature by 100°C.
Author: Publisher: ISBN: Category : Languages : en Pages : 17
Book Description
Support effects on catalytic reactions, especially of highly exothermic oxidation reactions, can be very significant. Since we had shown that a MoO3/SiO2 catalyst, especially when used in a double bed configuration with a Sr/La2O3 catalyst, can selectively oxidize methane to formaldehyde, the role of the SiO2 support was investigated. Therefore, partial oxidation of methane by oxygen to form formaldehyde, carbon oxides, and C2 products (ethane and ethene) has been studied over silica catalyst supports (fumed Cabosil and Grace 636 silica gel) in the 630-780°C temperature range under ambient pressure. When relatively high gas hourly space velocities (GHSV) were utilized, the silica catalysts exhibit high space time yields (at low conversions) for methane partial oxidation to formaldehyde, and the C2 hydrocarbons were found to be parallel products with formaldehyde. In general, the selectivities toward CO were high while those toward CO2 were low. Based on the present results obtained by a double catalyst bed experiment, the observations of product composition dependence on the variation of GHSV (i.e. gas residence time), and differences in apparent activation energies of formation of C2H6, and CH2O, a reaction mechanism is proposed for the activation of methane over the silica surface. This mechanism can explain the observed product distribution patterns (specifically the parallel formation of formaldehyde and C2 hydrocarbons).
Author: Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
At 550°C, the 1 wt % SO42−l wt % Sr/La2O3 catalyst, one of the most active catalyst for the selective conversion of methane at these moderate temperatures, showed a very good stability with a reactant mixture of CH4/air = 1/1 with GHSV = 70,040 l/kg catal/hr. During a 25 hr catalytic test, the conversion of CH4 and the C2 selectivity did not change, indicating good stability of the catalyst. At the same time, the CO2/CO ratio remained steady at about 2.2, but the C2{sup =}/C2 ratio shifted slightly with time from 0.74 to 0.68. The oxidative coupling of CH4 to C2-hydrocarbons was very sensitive at 550°C to the alteration of the CH4/air reactant ratio at GHSV = 70,040 l/kg catal/hr. It was observed that the conversion of CH4, the C2 selectivity, and the %yield of C2+ hydrocarbon products decreased very rapidly with increasing CH4/air ratio from 1 to 3-4. At the largest CH4/air ratio of 40.77 that was used utilized, the CH4 conversion was less than 0-5 C-mol%. The reverse process of decreasing the CH4/air ratio from (almost equal to)40 to 1 showed nearly reversible catalytic performance, but some deactivation was apparent at the lowest reactant ratios. The 1 wt % SO42−1 wt % Sr/La2O3 catalyst used in the experiments in which the CH4/air ratio was varied subsequently revealed a good stability in the CH4 conversion level during testing at 550°C for 15 hr (GHSV = 70,040 l/kg catal/hr and CH4/air = 1/1). Indeed, the C2+ selectivity even increased by 3 to 4 C-mol%. Increasing the temperature from 550 to 600°C resulted in a further recovery of the activity of the partially deactivated catalyst.
Author: Publisher: ISBN: Category : Languages : en Pages : 135
Book Description
Catalytic oxidation of methane to partial oxidation products, primarily formaldehyde and C2 hydrocarbons, was found to be directed by the catalyst used. In this project, it was discovered that a moderate oxidative coupling catalyst for C2 hydrocarbons, zinc oxide, is modified by addition of small amounts of Cu and Fe dopants to yield fair yields of formaldehyde. A similar effect was observed with Cu/Sn/ZnO catalysts, and the presence of a redox Lewis acid, Fe{sup III} or Sn{sup IV}, was found to be essential for the selectivity switch from C2 coupling products to formaldehyde. The principle of double doping with an oxygen activator (Cu) and the redox Lewis acid (Fe, Sn) was pursued further by synthesizing and testing the CuFe-ZSM-5 zeolite catalyst. The Cu{sup II}(ion exchanged) Fe{sup III}(framework)-ZSM-5 also displayed activity for formaldehyde synthesis, with space time yields exceeding 100 g/h-kg catalyst. However, the selectivity was low and earlier claims in the literature of selective oxidation of methane to methanol over CuFe-ZSM-5 were not reproduced. A new active and selective catalytic system (M=Sb, Bi, Sn)/SrO/La2O3 has been discovered for potentially commercially attractive process for the conversion of methane to C2 hydrocarbons, (ii) a new principle has been demonstrated for selectivity switching from C2 hydrocarbon products to formaldehyde in methane oxidations over Cu, Fe-doped zinc oxide and ZSM-5, and (iii) a new approach has been initiated for using ultrafine metal dispersions for low temperature activation of methane for selective conversions. Item (iii) continues being supported by AMOCO while further developments related to items (i) and (ii) are the objective of our continued effort under the METC-AMOCO proposed joint program.
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: