Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Technical Progress Report, September 8, 1992--November 30, 1992 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 Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Technical Progress Report, September 8, 1992--November 30, 1992 PDF full book. Access full book title Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Technical Progress Report, September 8, 1992--November 30, 1992 by . Download full books in PDF and EPUB format.
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 : 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 : 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 : 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 : 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 : 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 : 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 : 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: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: