Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, March--May 1994 PDF Download
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Author: Publisher: ISBN: Category : 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.
Author: Publisher: ISBN: Category : 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.
Author: Publisher: ISBN: Category : Languages : en Pages : 23
Book Description
A 1 wt% SO42−/1 wt% Sr/La2O3 catalyst has been shown by us to be one of the most active catalyst for the oxidative coupling of CH4 to C2 hydrocarbons. One of the by-products is CO2 and this is a potential strong poison for the formation of C2 products. Hence, various pretreatments of this catalyst were studied in terms of effect on the catalytic performance. Before the reaction was carried out at 500 or 550°C, the catalyst was pretreated in flowing air or He at 500, 700, or 800°C. Relative to the 500°C treatment, the pretreatment in air at 700°C only slightly decreased the C2 selectivity while the CO(subscript x) selectivity increased. This effect was larger when the pretreatment was carried out at 800°C. It was observed that the deactivation effect was slightly smaller when the pretreatments were carried out in He instead of air. For both air and He, the CH4, conversion and the C2 %yield showed more or less parallel changes (small decreases) with increasing pretreatment temperature. After a standard pretreatment (air, 500°C, 1 hr), the reaction temperature was increased stepwise from 500 to 700°C and then lowered to 550 (or 500)°C. It was observed that the catalytic performance showed deactivation towards the C2+ products. Decreasing stepwise the total flow rate (GHSV) of the reacting gas mixture (CH4/air = 1/1) from 70,175 to 5,388 l/kg catal/hr at a reaction temperature of 550°C caused large changes in both the activity and selectivity. After going back at 550°C to the original GHSV = 70,175 l/kg catal/hr, the temperature was increased stepwise up to 600°C. Up to 580°C, the catalytic activity and selectivity did not change very much.
Author: Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
Series of catalysts consisting of MoO3, V2O5, TiO2, and SnO2 impregnated onto oxide supports consisting of SiO2 (Cab-O-Sil), TiO2 or SnO2 were previously prepared and tested for the selective oxidation of methane to oxygenates, and it was found that the V2O5/SiO2 catalyst was the most active and most selective toward the formation of formaldehyde. These catalysts have been characterized by laser Raman spectroscopy after dehydration and during the methane oxidation reaction with a CH4/02 = 10/1 reaction mixture at 500°C in a continuous flow in situ reaction cell. With the V2O5/SiO2 catalyst (the most active catalyst among those studied), no significant structural changes were revealed by in situ Raman analyses, indicating that the fully oxidized surface sites were related to the high formaldehyde selectivivity. Over the V2O5/TiO2 and V2O5/SnO2 catalysts, CO and CO2 were the principal products produced by oxidation of methane. For the first time, in situ Raman analysis clearly showed that for these latter catalysts, the surface vanadium(V) oxide species were partially reduced under the steady-state reaction conditions. The performance of the V2O5/TiO2/SiO2 catalyst was similar to that of the V2O5TiO2 catalyst, consistent with the earlier observation that vanadia was largely bound to the titania overlayer. It appears that formaldehyde selectivity decreased with increasing catalyst reducibility, but no direct correlation of catalyst activity with reductibility was observed.
Author: Publisher: ISBN: Category : 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.
Author: Publisher: ISBN: Category : 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
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.
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