Selective Methane Oxidation Over Promoted Oxide Catalysts. Topical Report, September 8, 1992--September 7, 1996 PDF Download
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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.
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.
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 : 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 : 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.
Author: Publisher: ISBN: Category : Languages : en Pages : 19
Book Description
Sulfate anion was used to modify the surface basicity of 1 wt% Sr/La2O3, and catalytic tests were carried out to probe the selective oxidation of methane to C2 coupling products over these catalysts. Over a range of reaction temperatures of 500--700°C, most of the catalytic tests were carried out with a 1 wt% SO4 2−/1 wt% Sr/La2O3with a CH4/air = 1/1 reactant mixture at 1 atm and with a gas hourly space velocity (GHSV) = 70,000 l/kg catal/hr. The sulfated catalyst showed the largest improved catalytic effect at 500°C. Compared to the activity of the nonsulfated Sr/La2O3, the sulfated catalyst resulted in enhancement of the methane conversion, the C2 selectivity, and the yield of C2 products. In situ laser Raman spectroscopy was used to characterize the surface of sulfated and nonsulfated catalysts. Preliminary results indicate that the sulfate anion preferentially bonded to the Sr rather than to the La ions. The promoting effect of the acidic sulfate on the catalytic activity of basic Sr/La2O3 seems to be due to the inhibition of carbonate formation on the surface Sr ions.
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 : 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
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.
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