Gasification of potassium-intercalated and impregnated natural graphites

Ferguson, Ewen; Schlögl, Robert; Jones, William

doi:10.1016/0016-2361(84)90186-8

Cited by 8 publications

(4 citation statements)

References 13 publications

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“…In contrast, the fringe separation distances seem to stay constant. This is a hint that probably no intercalation compounds are formed, which has been theorized to be unlikely before . The K ions or salts might instead be placed at the end of the graphene layers and could, therefore, inhibit soot plain formation to lead to slightly lower actual fringe lengths.…”

Section: Resultsmentioning

confidence: 81%

“…This is ah int that probablyn oi ntercalation compounds are formed, which has been theorized to be unlikelyb efore. [66,67] The Ki ons or salts might instead be placed at the end of the graphene layersa nd could,t herefore, inhibit soot plain formation to lead to slightly lower actual fringe lengths. The tortuosity is slightly increased for soot that contains K 2 CO 3 compared to soot withouts alt and soot that contains KCl.…”

Section: High-resolution Transmission Electron Microscopymentioning

confidence: 99%

“…[15] The active phasec ould either be free K + + ions [58] and/or clusters of alkali metals, [62,65] which might be anchored through alkali metal phenolate groups on thesurface, but the latter do not really contributet ot he active species, [30,39,57,62,64] * alkali metal catalysts lead to an increased number of active sites without changingt he kinetics severely, [65] * there are probably no K-soot intercalates formed. [31,34,40,66,67] The variousa lkali metal salts can also be classified according to their reactivity.G enerally,t he reactivity increases throughout the group of alkali metals, [39,40,44,45,52] andR bh as ac omparable activity to K. There are also publicationso nc ertaint ypes of coal were the ordero ft he alkali metals was the other way around [14] or there was no specific order. [28] The order of reactivity of Ks alts with regard to the anionsd ecreases generally from K 2 CO 3 /KOH > KHCO 3 > KNO 3 > K 2 SO 4 % KCl, [33, 41-45, 49, 51] and KCl is the least reactive with almostn oa ctivity because of the formation of too-stable salts.…”

Section: Introductionmentioning

confidence: 99%

“… K facilitates compounds with low melting points or eutectic mixtures, K acts as an electron donor with surface oxygen as the electron acceptor (and subsequent formation of phenoxide species or gaseous K), K decreases the stability of carbonates on the surface, which leads to lower decomposition temperatures of the carbonates, general discussions between redox‐type oxygen‐ or electron‐transfer mechanisms or a combination of both, the high mobility of K compounds on the soot surface/the ability to act as a molten salt (sometimes described as a film of metallic K and K 2 O) and, therefore, a very good contact with the soot, promotion of a dissociative chemisorption of oxygen, K is also discussed to be the active phase in K‐bearing (oxidic) catalysts . The active phase could either be free K + ions and/or clusters of alkali metals, which might be anchored through alkali metal phenolate groups on the surface, but the latter do not really contribute to the active species, alkali metal catalysts lead to an increased number of active sites without changing the kinetics severely, there are probably no K‐soot intercalates formed …”

Section: Introductionmentioning

confidence: 99%

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Catalytic Effect of Potassium Compounds in Soot Oxidation

2017

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The combustion temperatures of soot in particulate filters can be decreased to exhaust gas temperatures by using catalysts. In addition to oxidic catalysts, alkali metal salts are very effective catalysts. Although soot is one of the world's most unwanted byproducts, combustion is still not fully understood. In this study, different soot mixed internally with salt samples were produced. All salts lead to a marked, salt‐ and salt‐content‐dependent decrease of the temperature‐programmed oxidation temperatures of maximum CO + CO2 emissions (Tmax), with K2CO3 being one of the most effective catalysts that leads to a decrease of the Tmax of up to 300 °C. Structural parameters of the internally mixed soot derived by using Raman microspectroscopy, SEM, and scanning mobility particle size analysis did not change significantly; BET areas showed slight trends to lower areas with increased salt content, but no substantial correlations were observed. In contrast, a correlation of the oxidation reactivity to the number distribution of the measured actual fringe lengths by using high‐resolution transmission electron microscopy and the peak areas measured by using EPR spectroscopy was found. Salts lead to a narrowing of the actual fringe length number distributions to lower sizes and to reduced EPR peak areas. This demonstrates that the salts influence the nanostructure of the graphene planes by shortening the planes and further substantiates that soot oxidation is at least partly based on electron transfer and not only oxygen transfer. EPR spectroscopy measurements indicate that the oxidation mechanism is based on a temperature‐dependent chemical equilibrium, which depends on the K+/anion binding strength.

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Section: Resultsmentioning

confidence: 81%

Section: High-resolution Transmission Electron Microscopymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Catalytic Effect of Potassium Compounds in Soot Oxidation

2017

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Carbons

Schlögl

2008

Handbook of Heterogeneous Catalysis

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The element carbon plays a multiple role in heterogeneous catalysis. In homogeneous catalysis it occurs of course as the most prominent constituent of ligand systems and will be treated as such there. Carbon-containing molecules are, in most catalytic applications, the substrates of the process under consideration. Deposits and polymers of carbon often occur as poisons on catalysts. Carbon deposition is the most severe problem in certain zeolite applications. In hydrogenation reactions carbon deposits are thought to act as modifiers for the activity of the catalyst and to provide selectivity by controlling the hydrogenationdehydrogenation activity of the metal part of the catalyst. Carbon deposits are even thought to constitute part of the active sites in some cases. Carbon is a prominent catalyst support material as it allows the anchoring of metal particles on a substrate which does not exhibit solid acid-base properties. Carbon is finally a catalyst in its own right allowing the activation of oxygen and chlorine for selective oxidation, chlorination and de-chlorination reactions. These multiple roles of the element carbon are in parallel with a complex structural chemistry giving rise to families of chemically vastly different modifications of the element. It is a special characteristic of carbon chemistry that many of these modifications cannot be obtained as phase-pure materials. This limits the exact knowledge of physical and chemical properties to a few archetype modifications, namely graphite and diamond. The reason for this poor definition of materials is found in the process of its formation. This is comprised of difficult to control polymerisation reactions. Such reactions will occur also in catalytic reactions with small organic molecules. The nature of carbon deposits will therefore reflect all the complexity of the bulk carbon materials. It is one aim of this article to describe the structural and chemical complexity of "carbon" or "soot" in order to provide an understanding of the frequently observed complexity of the chemical reactivity (e.g. in re-activation processes aiming at an oxidative removal of deposits). The surface chemistry of carbon which determines its interfacial properties is a rich field as a wide variety of surface functional groups are known to exist on carbon. The by far most important family of surface functional groups are those involving oxygen. Other prominent heteroatoms on the surface are hydrogen and nitrogen. This article focusses on the description and characterisation of oxygen surface functional groups. In the final section, selected case studies of carbon chemistry in catalysis will be discussed in order to illustrate characteristic properties of carbon materials as wanted or unwanted components in catalytic systems. Regarding the literature on basic properties of carbon materials, the reader is referred to the extensive collection of review papers published in the series Chemistry and Physics of Carbon. Editors P.L.

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Catalytic Gasification

Moulijn

Kapteijn

1986

Carbon and Coal Gasification

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Gasification of potassium-intercalated and impregnated natural graphites

Cited by 8 publications

References 13 publications

Catalytic Effect of Potassium Compounds in Soot Oxidation

Catalytic Effect of Potassium Compounds in Soot Oxidation

Carbons

Catalytic Gasification

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