43 research outputs found
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Selective methane oxidation over promoted oxide catalysts. Topical report, September 8, 1992--September 7, 1996
The objective of this research was to selectively oxidize methane to C{sub 2} 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 C{sub 2}{sup +} products over promoted SrO/La{sub 2}O{sub 3} catalysts; Task 2, selective methane oxidation to oxygenates; and Task 3, catalyst characterization and optimization. Principal accomplishments include the following: the 1 wt% SO{sub 4}{sup 2{minus}}/SrO/La{sub 2}O{sub 3} promoted catalyst developed here produced over 2 kg of C{sub 2} hydrocarbons/kg catalyst/hr at 550 C; V{sub 2}O{sub 5}/SiO{sub 2} catalysts have been prepared that produce up to 1.5 kg formaldehyde/kg catalyst/hr at 630 C with low CO{sub 2} 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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Selective Methane Oxidation Over Promoted Oxide Catalysts. Quarterly Report, September 1 - November 30, 1995
The objective of this research is the selective oxidation of methane to C{sub 2}H{sub 4} 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{degrees}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 {sup 51}V NMR and double catalyst bed experiments were conducted to demonstrate the unfavorable effect of the presence of bulk crystalline V{sub 2}O{sub 5} in V{sub 2}O{sub 5}-SiO{sub 2} xerogel catalysts on selective oxidation of methane to methanol and formaldehyde. Results are discussed
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Selective methane oxidation over promoted oxide catalysts. Quarterly report, June 1 - August 31, 1996
Further data analysis for the conversion of methane to oxygenates over high surface are V{sub 2}O{sub 5}/SiO{sub 2} 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 {sup 51}V 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
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Mechanisms and controlling characteristics of the catalytic oxidation of methane
Methane dissociation and oxygen activation have been found to be structure sensitive on different single crystal palladium surfaces. Geometrically restricted surfaces on Pd single crystal and polycrystalline surfaces using tetrachloroethylene and pentamethylcyclopentasiloxane have been formed and compared with surface structures formed using dichloromethane and chlorine. The adsorption and activation of O{sub 2}, CO, and H{sub 2}O on clean Pd surfaces and those containing the surface ensembles have also been investigated. To interpret high-resolution angle-resolved x-ray photoelectron spectra (HR AR-XPS), a new self-modeling method of resolving HR-XPS spectra was developed and applied to the experimental spectra. The effects of electron-accepting Cl, O{sub 2}, and H{sub 2}O adsobated on Cs/MoS{sub 2} were determined
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Mechanisms and controlling characteristics of the catalytic oxidation of methane
Progress has included (1) construction and installation of an ultraviolet photoelectron spectrometer (UPS) with power supply and pumping system that has been added as an attachment to the SCIENTA ESCA-300 instrument, (2) modification of the high resolution electron energy loss spectrometer (HREELS) to produce a stable ultra high vacuum (UHV) environment for initial experiments with a Pd(311) single crystal, (3) construction of a separate high vacuum system for preparation of surface doped model catalysts by chemical vapor deposition and pretreatment of a Pd(100) single crystal in this system, (4) carried out detailed experiments of methane activation and oxidation on Pd(679) using a high pressure reaction cell contained in a third ultra high vacuum system, (5) completion of adsorption/desorption studies of H{sub 2}, CO, and O{sub 2} on Pd(679), (6) utilized angle-resolved XPS to probe the diffraction characteristics and structure of the Pd(100) surface, (7) determination of the electronic surface structure of Pd(100) using angle-resolved UPS, and (8) computational analysis of oxygen overlayers on the PD(100) surface. Each of these is discussed in further detail below
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Selective methane oxidation over promoted oxide catalysts
Principal accomplishments have been achieved in all three areas of selective catalytic oxidation of methane that have been pursued in this research project. These accomplishments are centered on the development of catalyst systems that produce high space time yields of C{sub 2} hydrocarbon products, formaldehyde, and methanol from methane/air mixtures at moderate temperatures and at ambient pressure. The accomplishments can be summarized as the following: the SO{sub 4}{sup 2{minus}}/SrO/La{sub 2}O{sub 3} catalyst developed here has been further optimized to produce 2 kg of C{sub 2} hydrocarbons/kg catalyst/hr at 550C; V{sub 2}O{sub 5}SiO{sub 2} catalysts have been prepared that produce up to 1.5 kg formaldehyde/kg catalyst/hr at 630C with CO{sub 2} selectivities; and a novel dual bed catalyst system has been designed and tested that produces over 100 g methanol/kg catalyst/hr at 600C
Catalytic Synthesis of Oxygenates: Mechanisms, Catalysts and Controlling Characteristics
This research focused on catalytic synthesis of unsymmetrical ethers as a part of a larger program involving oxygenated products in general, including alcohols, ethers, esters, carboxylic acids and their derivatives that link together environmentally compliant fuels, monomers, and high-value chemicals. The catalysts studied here were solid acids possessing strong Brønsted acid functionalities. The design of these catalysts involved anchoring the acid groups onto inorganic oxides, e.g. surface-grafted acid groups on zirconia, and a new class of mesoporous solid acids, i.e. propylsulfonic acid-derivatized SBA-15. The former catalysts consisted of a high surface concentration of sulfate groups on stable zirconia catalysts. The latter catalyst consists of high surface area, large pore propylsulfonic acid-derivatized silicas, specifically SBA-15. In both cases, the catalyst design and synthesis yielded high concentrations of acid sites in close proximity to one another. These materials have been well-characterization in terms of physical and chemical properties, as well as in regard to surface and bulk characteristics. Both types of catalysts were shown to exhibit high catalytic performance with respect to both activity and selectivity for the bifunctional coupling of alcohols to form ethers, which proceeds via an efficient SN2 reaction mechanism on the proximal acid sites. This commonality of the dual-site SN2 reaction mechanism over acid catalysts provides for maximum reaction rates and control of selectivity by reaction conditions, i.e. pressure, temperature, and reactant concentrations. This research provides the scientific groundwork for synthesis of ethers for energy applications. The synthesized environmentally acceptable ethers, in part derived from natural gas via alcohol intermediates, exhibit high cetane properties, e.g. methylisobutylether with cetane No. of 53 and dimethylether with cetane No. of 55-60, or high octane properties, e.g. diisopropylether with blending octane No. of 105, and can replace aromatics in liquid fuels
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Catalytic Synthesis of Oxygenates: Mechanisms, Catalysts and Controlling Characteristics
This research focused on catalytic synthesis of unsymmetrical ethers as a part of a larger program involving oxygenated products in general, including alcohols, ethers, esters, carboxylic acids and their derivatives that link together environmentally compliant fuels, monomers, and high-value chemicals. The catalysts studied here were solid acids possessing strong BrÃÂÃÂÃÂønsted acid functionalities. The design of these catalysts involved anchoring the acid groups onto inorganic oxides, e.g. surface-grafted acid groups on zirconia, and a new class of mesoporous solid acids, i.e. propylsulfonic acid-derivatized SBA-15. The former catalysts consisted of a high surface concentration of sulfate groups on stable zirconia catalysts. The latter catalyst consists of high surface area, large pore propylsulfonic acid-derivatized silicas, specifically SBA-15. In both cases, the catalyst design and synthesis yielded high concentrations of acid sites in close proximity to one another. These materials have been well-characterization in terms of physical and chemical properties, as well as in regard to surface and bulk characteristics. Both types of catalysts were shown to exhibit high catalytic performance with respect to both activity and selectivity for the bifunctional coupling of alcohols to form ethers, which proceeds via an efficient SN2 reaction mechanism on the proximal acid sites. This commonality of the dual-site SN2 reaction mechanism over acid catalysts provides for maximum reaction rates and control of selectivity by reaction conditions, i.e. pressure, temperature, and reactant concentrations. This research provides the scientific groundwork for synthesis of ethers for energy applications. The synthesized environmentally acceptable ethers, in part derived from natural gas via alcohol intermediates, exhibit high cetane properties, e.g. methylisobutylether with cetane No. of 53 and dimethylether with cetane No. of 55-60, or high octane properties, e.g. diisopropylether with blending octane No. of 105, and can replace aromatics in liquid fuels