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A radical twist to the versatile behavior of iron in selective methane activation.

Ruitenbeek M, Weckhuysen BM - Angew. Chem. Int. Ed. Engl. (2014)

View Article: PubMed Central - PubMed

Affiliation: Hydrocarbons R&D, The Dow Chemical Company, Haven 443, P.O. Box, 4530 AA Terneuzen (The Netherlands). mruitenbeek@dow.com.

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The availability of large reserves of methane, which is the main component of most natural gas, makes it a very important feedstock molecule for the production of base chemicals (e.g. ethylene, propylene, and aromatics) and energy carriers (i.e. transportation fuels)... Current commercial routes for methane activation involve the conversion of methane into syngas, which is a mixture of CO and H2, and its subsequent conversion into hydrocarbons such as propylene, aromatics, and fuels.[– More specifically, methanol-to-hydrocarbon (MTH) catalysis involves the catalytic conversion of syngas-derived methanol (or dimethyl ether) into mixtures of, for example, ethylene, propylene, and aromatics, depending on the specific zeolite material and reaction conditions applied... An example of such an approach is the oxidative coupling of methane (OCM), generating methyl radicals in the gas phase which then recombine to ethylene. ,  Unfortunately, the currently developed OCM catalyst materials and related reactor (membrane) designs do not provide the required performance, both in terms of activity and more importantly selectivity (e.g. CO2 generation and formation of coke deposits)... In a recent study, Guo and co-workers reported on a new catalyst material, which could circumvent the disadvantages of, for example, OCM technology... It was found that the novel catalyst, consisting of lattice-confined single iron sites (Figure 1), produces in a nonoxidative manner high yields of ethylene, benzene, and naphthalene... Very remarkable is the negligible amount of coke deposits formed at the relatively high operational temperature of 1363 K, which results in an unprecedented overall selectivity towards ethylene and aromatics of >99 % with a selectivity towards ethylene of 48 % for a methane conversion of 48 %... The active site in this catalyst material is proposed to consist of a single iron atom, coordinated to one silicon and two carbon atoms (Figure 1)... This conclusion has been derived from extended X-ray absorption fine structure (EXAFS) studies, complemented with high-angle dark field (HAADF) scanning transmission electron microscopy (STEM) measurements... In this context it is important to mention the unique synthesis method employed for making the low-surface-area catalyst material containing lattice-confined single iron sites, which is referred to the 0.5 wt % Fe@SiO2 catalyst... A ferrous metasilicate (Fe2SiO4), better known as fayalite, is fused with SiO2 at very high temperatures (1973 K) in air, and the resulting material is ball-milled and treated with aqueous HNO3... Benzene in itself can also undergo dehydrogenation and further chain growth and cyclization leads to the formation of naphthalene... In contrast to OCM chemistry, ROOη radicals are avoided, which significantly reduces unwanted peroxide routes that typically lead to large amounts of oxygenates and/or CO2... The unique feature of the catalytic route reported by Guo et al. is that it starts with cheap methane feedstock and that several of the regular radical pathways appear to be blocked... The biggest mystery of the catalytic chemistry described by Guo et al. is the (almost) complete absence of the unwanted formation of coke deposits... This is a very encouraging result in the ongoing quest to develop selective routes for the direct utilization of methane.

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Structural motif of the designed 0.5 wt % Fe@SiO2 catalyst material, active in the selective activation of methane and producing ethylene, benzene, and naphthalene without the substantial formation of coke deposits at high reaction temperatures.
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fig01: Structural motif of the designed 0.5 wt % Fe@SiO2 catalyst material, active in the selective activation of methane and producing ethylene, benzene, and naphthalene without the substantial formation of coke deposits at high reaction temperatures.

Mentions: In a recent study, Guo and co-workers reported on a new catalyst material, which could circumvent the disadvantages of, for example, OCM technology.7 It was found that the novel catalyst, consisting of lattice-confined single iron sites (Figure 1), produces in a nonoxidative manner high yields of ethylene, benzene, and naphthalene. Very remarkable is the negligible amount of coke deposits formed at the relatively high operational temperature of 1363 K, which results in an unprecedented overall selectivity towards ethylene and aromatics of >99 % with a selectivity towards ethylene of 48 % for a methane conversion of 48 %. Site isolation has been argued by the authors to be crucial, as the absence of adjacent iron sites prevents catalytic C–C coupling reactions, which may subsequently lead to the generation of coke deposits.


A radical twist to the versatile behavior of iron in selective methane activation.

Ruitenbeek M, Weckhuysen BM - Angew. Chem. Int. Ed. Engl. (2014)

Structural motif of the designed 0.5 wt % Fe@SiO2 catalyst material, active in the selective activation of methane and producing ethylene, benzene, and naphthalene without the substantial formation of coke deposits at high reaction temperatures.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4225476&req=5

fig01: Structural motif of the designed 0.5 wt % Fe@SiO2 catalyst material, active in the selective activation of methane and producing ethylene, benzene, and naphthalene without the substantial formation of coke deposits at high reaction temperatures.
Mentions: In a recent study, Guo and co-workers reported on a new catalyst material, which could circumvent the disadvantages of, for example, OCM technology.7 It was found that the novel catalyst, consisting of lattice-confined single iron sites (Figure 1), produces in a nonoxidative manner high yields of ethylene, benzene, and naphthalene. Very remarkable is the negligible amount of coke deposits formed at the relatively high operational temperature of 1363 K, which results in an unprecedented overall selectivity towards ethylene and aromatics of >99 % with a selectivity towards ethylene of 48 % for a methane conversion of 48 %. Site isolation has been argued by the authors to be crucial, as the absence of adjacent iron sites prevents catalytic C–C coupling reactions, which may subsequently lead to the generation of coke deposits.

View Article: PubMed Central - PubMed

Affiliation: Hydrocarbons R&D, The Dow Chemical Company, Haven 443, P.O. Box, 4530 AA Terneuzen (The Netherlands). mruitenbeek@dow.com.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

The availability of large reserves of methane, which is the main component of most natural gas, makes it a very important feedstock molecule for the production of base chemicals (e.g. ethylene, propylene, and aromatics) and energy carriers (i.e. transportation fuels)... Current commercial routes for methane activation involve the conversion of methane into syngas, which is a mixture of CO and H2, and its subsequent conversion into hydrocarbons such as propylene, aromatics, and fuels.[– More specifically, methanol-to-hydrocarbon (MTH) catalysis involves the catalytic conversion of syngas-derived methanol (or dimethyl ether) into mixtures of, for example, ethylene, propylene, and aromatics, depending on the specific zeolite material and reaction conditions applied... An example of such an approach is the oxidative coupling of methane (OCM), generating methyl radicals in the gas phase which then recombine to ethylene. ,  Unfortunately, the currently developed OCM catalyst materials and related reactor (membrane) designs do not provide the required performance, both in terms of activity and more importantly selectivity (e.g. CO2 generation and formation of coke deposits)... In a recent study, Guo and co-workers reported on a new catalyst material, which could circumvent the disadvantages of, for example, OCM technology... It was found that the novel catalyst, consisting of lattice-confined single iron sites (Figure 1), produces in a nonoxidative manner high yields of ethylene, benzene, and naphthalene... Very remarkable is the negligible amount of coke deposits formed at the relatively high operational temperature of 1363 K, which results in an unprecedented overall selectivity towards ethylene and aromatics of >99 % with a selectivity towards ethylene of 48 % for a methane conversion of 48 %... The active site in this catalyst material is proposed to consist of a single iron atom, coordinated to one silicon and two carbon atoms (Figure 1)... This conclusion has been derived from extended X-ray absorption fine structure (EXAFS) studies, complemented with high-angle dark field (HAADF) scanning transmission electron microscopy (STEM) measurements... In this context it is important to mention the unique synthesis method employed for making the low-surface-area catalyst material containing lattice-confined single iron sites, which is referred to the 0.5 wt % Fe@SiO2 catalyst... A ferrous metasilicate (Fe2SiO4), better known as fayalite, is fused with SiO2 at very high temperatures (1973 K) in air, and the resulting material is ball-milled and treated with aqueous HNO3... Benzene in itself can also undergo dehydrogenation and further chain growth and cyclization leads to the formation of naphthalene... In contrast to OCM chemistry, ROOη radicals are avoided, which significantly reduces unwanted peroxide routes that typically lead to large amounts of oxygenates and/or CO2... The unique feature of the catalytic route reported by Guo et al. is that it starts with cheap methane feedstock and that several of the regular radical pathways appear to be blocked... The biggest mystery of the catalytic chemistry described by Guo et al. is the (almost) complete absence of the unwanted formation of coke deposits... This is a very encouraging result in the ongoing quest to develop selective routes for the direct utilization of methane.

No MeSH data available.