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Languages : en
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Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, September-November, 1994
Da yu de han diao yu de
Author: Selective Methane Oxidation Over Promoted Oxide Catalyst. Quarterly Report, September--November 1993
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Languages : en
Pages : 9
Book Description
Dispersed metal oxide catalysts have been prepared and tested for selective oxidation of methane. The catalysts were based on multivalent cations impregnated into a number of different oxide supports: MoO3/SiO2, V2O5/SiO2, V2O5/MoO3/SiO2, V2O5/TiO2, SnO2/SiO2, and V2O5/SnO2. Among the dispersed metal oxide catalysts studied this quarter, the most active catalyst was clearly the V2O5/SiO2 catalyst. High surface area silica samples impregnated with 1--5 wt% V2O5 were found to be active catalysts with low selectivity toward CO2. Although CO was the major product, appreciable selectivities toward formaldehyde were also observed. Indeed, with the V2O5/SiO2 catalysts, very high space time yields of formaldehyde of> 1 kg CH2O/kg catal/h could be obtained even though conventional single pass %yields were
Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, September 1 - November 30, 1995
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Languages : en
Pages : 13
Book Description
The objective of this research is the selective oxidation of methane to C2H4 hydrocarbons and to oxygenates, in particular formaldehyde and methanol. Air, oxygen, or carbon dioxide rather than nitrous oxide, are utilized as the oxidizing gas at high gas hourly space velocity but mild reaction conditions (500-700°C, 1 atm total pressure). All the investigated processes are catalytic, aiming at minimizing gas phase reactions that are difficult to control. During this quarter, solid state 51V NMR and double catalyst bed experiments were conducted to demonstrate the unfavorable effect of the presence of bulk crystalline V2O5 in V2O5-SiO2 xerogel catalysts on selective oxidation of methane to methanol and formaldehyde. Results are discussed.
Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, March--May 1994
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Languages : en
Pages : 10
Book Description
Experimental work aiming at developing active catalysts for selective oxidation of methane to methanol was started in this quarter. Some of the experiments used a double catalyst bed design and with H2O as cofeed. The first catalyst bed, which serves as CH3 radical generator, was chosen to be 1 wt % SO42−/Sr/La2O3, as this catalyst exhibits remarkable activity and selectivity at lower temperature (500°C--550°C). A few transition metal oxides were used as the second catalyst bed to react with CH3 to form CH3O−M species, which was then hydrolyzed to form CH3OH. It was found that unsupported metal oxides ZrO2, Y2O3, SrO; Fe2O3, MnO2, Cr2O3, CaO, and MgO did not produce CH3OH between 430°C and 600°C when used as the only catalysts, while MoO3 supported on silica produced CH30H in the temperature range of 430°C--480°C under the current single-bed reactor configuration. However, when the double-bed configuration was used with the 1 wt % SO42−/Sr/La2O3 as the first methyl radical generating catalyst bed, CH30H was observed when ZrO2and Y2O3 were used as the second bed catalysts. Preliminary quantitative analysis showed that the ability of producing CH3OH was in the order of unsupported Y2O3> unsupported ZrO2> MoO3 on silica. For all of these cases, the CH3OH space time yield was within a dozen grams per kilogram catalyst per hour.
Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Technical Progress Report, September 8, 1992--November 30, 1992
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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).
Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Technical Progress Report, June 1, 1993--August 31, 1993
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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.
وظيفة مؤسسات اعداد المعلمين
Author: Energy Research Abstracts
Author: Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, December 1, 1995--February 29, 1996
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ISBN:
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Languages : en
Pages : 12
Book Description
In a systematic study with a CH4/air reactant mixture at 600 C and 0.1 MPa, it is demonstrated that among eight Cab-O-Sil supported redox transition metal oxide catalysts, a V2O5/SiO2 catalyst exhibited the highest productivities of formaldehyde and methanol. The effect of steam on enhancing the space time yields of the oxygenates was observed with the catalysts that were studied with this third component in the reaction mixture. With the vanadia-containing catalyst, it was shown that a loading of 2 wt% of V2O5 on SiO2 produced the highest conversion of methane from a CH4/air/steam = 4/1/1 reactant mixture and the highest productivities of both CH3OH and HCHO. It was also shown that increasing the reactant flow rate (thereby decreasing the contact time) increased the space time yield of methanol but decreased the overall methane conversion level.