Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, June 1 - August 31, 1996 PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages : 13
Book Description
Further data analysis for the conversion of methane to oxygenates over high surface are V2O5/SiO2 xerogel catalysts that were synthesized by a sol-gel process have been carried out. As previously described the vanadia loading of the catalysts was varied between 0-25 wt%. Turnover numbers (T.O.N.) have been calculated for methane conversion to products and for the synthesis of methanol and formaldehyde, where T.O.N. is defined as molecules converted or formed per dispersed tetrahedrally coordinated vanadium atom ad determined by 51V NMR analyses. It is found that highly dispersed tetrahedrally coordinated V{sup 5+} is the active site for the selective conversion of methane to methanol and formaldehyde.
Author: Publisher: ISBN: Category : Languages : en Pages : 13
Book Description
Further data analysis for the conversion of methane to oxygenates over high surface are V2O5/SiO2 xerogel catalysts that were synthesized by a sol-gel process have been carried out. As previously described the vanadia loading of the catalysts was varied between 0-25 wt%. Turnover numbers (T.O.N.) have been calculated for methane conversion to products and for the synthesis of methanol and formaldehyde, where T.O.N. is defined as molecules converted or formed per dispersed tetrahedrally coordinated vanadium atom ad determined by 51V NMR analyses. It is found that highly dispersed tetrahedrally coordinated V{sup 5+} is the active site for the selective conversion of methane to methanol and formaldehyde.
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 : 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 : 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 : 116
Book Description
The objective of this research was to selectively oxidize methane to C2 hydrocarbons and to oxygenates, in particular formaldehyde and methanol, in high space time yields using air at the oxidant under milder reaction conditions that heretofore employed over industrially practical oxide catalysts. The research carried out under this US DOE-METC contract was divided into the following three tasks: Task 1, maximizing selective methane oxidation to C2 products over promoted SrO/La2O3 catalysts; Task 2, selective methane oxidation to oxygenates; and Task 3, catalyst characterization and optimization. Principal accomplishments include the following: the 1 wt% SO42−/SrO/La2O3 promoted catalyst developed here produced over 2 kg of C2 hydrocarbons/kg catalyst/hr at 550 C; V2O5/SiO2 catalysts have been prepared that produce up to 1.5 kg formaldehyde/kg catalyst/hr at 630 C with low CO2 selectivities; and a novel dual bed catalyst system has been designed and utilized to produce over 100 g methanol/kg catalyst/hr at 600 C with the presence of steam in the reactant mixture.
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