Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Report September November 1994 written by and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Report September 1 November 30 1995 written by and published by . This book was released on 1995 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Report December 1 1995 February 29 1996 written by and published by . This book was released on 1996 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Da yu de han diao yu de written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalyst Quarterly Report September November 1993 written by and published by . This book was released on 1994 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Technical Progress Report June 1 1993 August 31 1993 written by and published by . This book was released on 1993 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Technical Progress Report September 8 1992 November 30 1992 written by and published by . This book was released on 1993 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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).
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Technical Progress Report March 1 1993 May 31 1993 written by and published by . This book was released on 1993 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Topical Report September 8 1992 September 7 1996 written by and published by . This book was released on 1996 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Technical Progress Report December 1 1992 February 28 1993 written by and published by . This book was released on 1993 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Report March May 1994 written by and published by . This book was released on 1994 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Report June 1 August 31 1996 written by and published by . This book was released on 1996 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Selective Methane Oxidation Over Promoted Oxide Catalysts Quarterly Report March 1 May 31 1996 written by and published by . This book was released on 1996 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Methane Oxidation Over Dual Redox Catalysts Final Report written by and published by . This book was released on 1992 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalytic oxidation of methane to partial oxidation products, primarily formaldehyde and C2 hydrocarbons, was found to be directed by the catalyst used. In this project, it was discovered that a moderate oxidative coupling catalyst for C2 hydrocarbons, zinc oxide, is modified by addition of small amounts of Cu and Fe dopants to yield fair yields of formaldehyde. A similar effect was observed with Cu/Sn/ZnO catalysts, and the presence of a redox Lewis acid, Fe{sup III} or Sn{sup IV}, was found to be essential for the selectivity switch from C2 coupling products to formaldehyde. The principle of double doping with an oxygen activator (Cu) and the redox Lewis acid (Fe, Sn) was pursued further by synthesizing and testing the CuFe-ZSM-5 zeolite catalyst. The Cu{sup II}(ion exchanged) Fe{sup III}(framework)-ZSM-5 also displayed activity for formaldehyde synthesis, with space time yields exceeding 100 g/h-kg catalyst. However, the selectivity was low and earlier claims in the literature of selective oxidation of methane to methanol over CuFe-ZSM-5 were not reproduced. A new active and selective catalytic system (M=Sb, Bi, Sn)/SrO/La2O3 has been discovered for potentially commercially attractive process for the conversion of methane to C2 hydrocarbons, (ii) a new principle has been demonstrated for selectivity switching from C2 hydrocarbon products to formaldehyde in methane oxidations over Cu, Fe-doped zinc oxide and ZSM-5, and (iii) a new approach has been initiated for using ultrafine metal dispersions for low temperature activation of methane for selective conversions. Item (iii) continues being supported by AMOCO while further developments related to items (i) and (ii) are the objective of our continued effort under the METC-AMOCO proposed joint program.
