Heterogeneous-Homogeneous Mechanism of Catalytic Oxidation

Garibyan, T.A.; Margolis, L. Ya.

doi:10.1080/01614948909349935

Cited by 43 publications

(24 citation statements)

References 29 publications

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“…13 This classification may have to be revised as multiple research groups are blurring the borders between homogeneous, heterogeneous, and enzymatic catalyses. 19 Homogeneous catalyses are those where the catalyst is in the same phase (either liquid or gas) as the reactants and products. Heterogeneous catalysts are those where the catalyst is in a separate phase than the reactants.…”

Section: -18mentioning

confidence: 99%

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

Lin

Huber

2009

Energy Environ. Sci.

426

256

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Lignocellulosic biofuels have a tremendous potential to reduce problems caused by our dependence on fossil fuels. The current roadblock with biofuels is the lack of economical conversion technologies. Heterogeneous catalysis offers immense potential in helping to make lignocellulosic biofuels a commercial reality. In this article we discuss the central role of heterogeneous catalysis in biomass conversion. We review the science of catalysis and the different routes to make biofuels. During the last several decades multiple new spectroscopic, theoretical, and synthesis tools are available that allow us to study catalysis at a molecular level. These new tools will allow us to rapidly develop new catalytic processes for the production of cost-efficient lignocellulosic biofuels.

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Section: -18mentioning

confidence: 99%

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

Lin

Huber

2009

Energy Environ. Sci.

426

256

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“…The reaction mixture with CH 4 /O 2 ratio of 5 without diluent gas was used for oxidative methane pyrolysis. The purity of CH 4 and O 2 gases was greater than 99.99% and the gases were dehydrated and purified with suitable filters. The reactor effluent gases were analyzed using on-line gas chromatography system and H 2 product was separately analyzed with a TCD in another gas chromatography.…”

Section: Methodsmentioning

confidence: 99%

“…3 A decrease in the CH 4 /O 2 ratio drives the production of C n (n≥2) hydrocarbons, but it favors transfer of the reaction from the reaction on catalyst surface to the gas phase. 4 Nersesyan et al 5 found the presence of methyl-and hydro-peroxy radicals in the gas phase for methane oxidation over SiO 2 in the 843-903 K temperature range using the kinetic radical freezing method, which enables us to consider that methyl radical can be formed on the surface of quartz reactor itself even at the given low temperature although the nature of active site on silica surface is not fully understood. For these reasons, to understand the reaction mechanism and optimize the performances for oxidative coupling of methane using a quartz flow reactor, kinetic investigation of oxidative methane pyrolysis in the absence of catalyst is required.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

“…1,2 In CH 4 /O 2 reaction, the reaction pathway is generally determined by the CH 4 /O 2 ratio. 3 A decrease in the CH 4 /O 2 ratio drives the production of C n (n≥2) hydrocarbons, but it favors transfer of the reaction from the reaction on catalyst surface to the gas phase. 4 Nersesyan et al 5 found the presence of methyl-and hydro-peroxy radicals in the gas phase for methane oxidation over SiO 2 in the 843-903 K temperature range using the kinetic radical freezing method, which enables us to consider that methyl radical can be formed on the surface of quartz reactor itself even at the given low temperature although the nature of active site on silica surface is not fully understood.…”

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confidence: 99%

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Kinetic Investigation of Oxidative Methane Pyrolysis at High CH₄/O₂Ratio in a Quartz Flow Microreactor below 1073 K

Cho

Choi

Kim³

et al. 2008

Bulletin of the Korean Chemical Society

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Oxidative coupling of methane in the presence of metal oxide catalyst generally takes place in the temperature range of 873-1173 K and methyl radical is generated on the catalyst surface and coupled into C 2 compounds in the gas phase.1,2 In CH 4 /O 2 reaction, the reaction pathway is generally determined by the CH 4 /O 2 ratio.3 A decrease in the CH 4 /O 2 ratio drives the production of C n (n≥2) hydrocarbons, but it favors transfer of the reaction from the reaction on catalyst surface to the gas phase.4 Nersesyan et al. 5 found the presence of methyl-and hydro-peroxy radicals in the gas phase for methane oxidation over SiO 2 in the 843-903 K temperature range using the kinetic radical freezing method, which enables us to consider that methyl radical can be formed on the surface of quartz reactor itself even at the given low temperature although the nature of active site on silica surface is not fully understood. For these reasons, to understand the reaction mechanism and optimize the performances for oxidative coupling of methane using a quartz flow reactor, kinetic investigation of oxidative methane pyrolysis in the absence of catalyst is required. Oxidative methane pyrolysis is known to be composed of many elementary reactions 6,7 and influenced by temperature, space velocity, mixture composition, and additives.8 Until now, various flow reactors have been designed and examined for the reaction above 1473 K.9-12 However, few results have been reported for the reaction in the temperature range of 873-1173 K where oxidative coupling of methane occurs. In this work, oxidative methane pyrolysis was carried out in an empty quartz reactor at various flow rates of CH 4 /O 2 reaction mixture in the temperature range of 873-1073 K and a catalytic effect of quartz reactor itself on the reaction was investigated. ExperimentalOxidative methane pyrolysis was performed in a quartz flow microreactor which was made of quartz tubing with a smaller inner diameter of 3.81 mm in order to minimize a thermal gradient in the reactor. The quartz tube was coiled itself round with five turns so as to give a larger capacity of the reactor as far as possible. The reaction volume located in the constant temperature zone of a muffle furnace was 4.23 cm 3 . Inlet and outlet tubes in the reactor were filled with silica wool in order to reduce the dead volume. The reaction mixture with CH 4 /O 2 ratio of 5 without diluent gas was used for oxidative methane pyrolysis. The purity of CH 4 and O 2 gases was greater than 99.99% and the gases were dehydrated and purified with suitable filters. The reactor effluent gases were analyzed using on-line gas chromatography system and H 2 product was separately analyzed with a TCD in another gas chromatography. The residence time of reaction mixture was calculated by the gas phase volume (4.23 cm 3 )/the total flow rate (cm 3 /s). The details of kinetic experiments were described in the previous papers. 13,14 In this work, there was no coke deposition in the reactor. H 2 , CO, C 2 hydrocarbons, and H 2 O ...

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Radicals in Catalysis – Heterogeneous

Sojka

Giamello

Paganini

2002

Encyclopedia of Catalysis

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Several reactions in heterogeneous catalysis take place via radical intermediates. The present article illustrates the typical aspects of the radical chemistry in heterogeneous catalysis that very often differ from those in the radical chemistry in fluid homogeneous phases because of the role of the surface in the generation, stabilization, and transformation of radical species. The various routes for the formation of radicals on a surface will be taken into consideration including electron transfer, atom transfer, and molecular dissociation. A particular emphasis is given to the electron magnetic resonance techniques, which have the paramount role in the detection and also in the description of the radical species because of their high sensitivity that allows the detection of low abundance species. In the final part of the article some selected examples of heterogeneous catalytic processes involving radical steps will be discussed with particular emphasis on catalytic oxidation on metal oxides.

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Heterogeneous-Homogeneous Mechanism of Catalytic Oxidation

Cited by 43 publications

References 29 publications

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

Kinetic Investigation of Oxidative Methane Pyrolysis at High CH₄/O₂Ratio in a Quartz Flow Microreactor below 1073 K

Radicals in Catalysis – Heterogeneous

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Heterogeneous-Homogeneous Mechanism of Catalytic Oxidation

Cited by 43 publications

References 29 publications

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

Kinetic Investigation of Oxidative Methane Pyrolysis at High CH4/O2Ratio in a Quartz Flow Microreactor below 1073 K

Radicals in Catalysis – Heterogeneous

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Product

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Kinetic Investigation of Oxidative Methane Pyrolysis at High CH₄/O₂Ratio in a Quartz Flow Microreactor below 1073 K