Characterization of Mn–Na2WO4/SiO2 and Mn–Na2WO4/MgO catalysts for the oxidative coupling of methane

Elkins, Trenton W.; Hagelin‐Weaver, Helena E.

doi:10.1016/j.apcata.2015.02.040

Cited by 88 publications

(60 citation statements)

References 34 publications

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“…[1,2,9,11,14] In our previous study, [1d] we confirmed that Mn and Ware not essential components for the selective OCM reaction. However, H 2 Owas identified as ak ey reactant (wet condition).…”

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“…[10] Thep eak intensity of Na 1s was located at 1072.0 eV,w hich corresponds to Na 1s of Na 2 WO 4 and is consistent with the reported value. [11] To explore the surface state of Na 2 WO 4 in the OH radical generation condition at 800 8 8C, am ixture of O 2 and H 2 Ow as introduced into the flowing reaction cell for AP-XPS. [10] Thep resence of freestate O 2 and H 2 Og ases was confirmed based on the observation of the photoemission features of the O1sp eaks (pink and blue line in Figure 3b and red line in Figure 3e) because they appear at arelatively higher binding energy than those of adsorbed species by afew eV.T he peak positions at 539.1 and 535.8 eV were assigned to O 2 and H 2 Oi nt he gas phase,r espectively,a nd are consistent with the references.…”

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confidence: 99%

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Integrated In Situ Characterization of a Molten Salt Catalyst Surface: Evidence of Sodium Peroxide and Hydroxyl Radical Formation

et al. 2017

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Sodium-based catalysts (sucha sN a 2 WO 4 )w ere proposed to selectively catalyze OH radical formation from H 2 Oa nd O 2 at high temperatures.T his reaction mayp roceed on molten salt state surfaces owing to the lower melting point of the used Na salts compared to the reaction temperature.T his study provides direct evidence of the molten salt state of Na 2 WO 4 ,which can form OH radicals,using in situ techniques including X-ray diffraction (XRD), scanning transmission electron microscopy( STEM), laser induced fluorescence (LIF) spectrometry,a nd ambient-pressure X-rayp hotoelectron spectroscopy(AP-XPS). As aresult, Na 2 O 2 species,which were hypothesized to be responsible for the formation of OH radicals,h ave been identified on the outer surfaces at temperatures of ! 800 8 8C, and these species are useful for various gasphase hydrocarbon reactions,i ncluding the selective transformation of methane to ethane.Gas-phase radical chemistry involving OH radicals plays acrucial role in the oxidative coupling of methane (OCM), [1] the dehydrogenation of ethane, [2] atmospheric chemistry, [3] and combustion reactions.[4] Thec atalytic generation of OH radicals from O 2 and H 2 Oc an occur on Pt metal and alkali earth oxides at high temperatures (> 700 8 8C).[5] Alkaline metal containing catalysts (that is,N as upported on oxide) enhanced the rate of H 2 Oactivation in the presence of O 2 and enhanced both the CH 4 conversion rate and C 2 selectivity during OCM.[1] Otsuka et al. demonstrated that Na 2 O 2 reacts with CH 4 to form methyl radicals at relatively low temperatures.[6] Recently,k inetic evidence suggests that H 2 Oi s involved in the activation of CH 4 via the quasi-equilibrated formation of OH radicals when aN a-containing catalyst is used.[1] In as imilar context, an in situ Raman spectroscopic study identified Ba species on MgO that formed peroxide ions and was proposed as the active sites.[7] However,d irect evidence of the formation of this sodium peroxide species and an OH radical product are lacking. Here,i nsitu studies performed at high temperatures using different in situ characterization techniques were performed to identify the authentic active species during catalysis responsible for the OCM reaction. We report evidence for the formation of Na 2 O 2 and OH radicals during the catalysis,and these species play asignificant role in high-temperature gas-phase chemistry.Ad etailed kinetic investigation that was focused on the effects of H 2 Oo nt he CH 4 /O 2 reaction was reported in our previous studies.[1] Briefly,the kinetic expression for the CH 4 / O 2 reaction on Na-based catalysts at low conversion levels is given in (1):Thef irst term corresponds to CH 4 activation via surface O (O*), which is quasi-equilibrated with gas-phase O 2 (dry condition). Thes econd term corresponds to CH 4 activation via an OH radical that is formed from O 2 and H 2 Oi nq uasiequilibrated steps (wet condition). Among the studied catalysts,t he Na 2 WO 4 /SiO 2 catalyst exhibited the highest contributi...

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Integrated In Situ Characterization of a Molten Salt Catalyst Surface: Evidence of Sodium Peroxide and Hydroxyl Radical Formation

et al. 2017

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“…The increase of the C 2 H 4 :C 2 H 6 ratio is caused by an increase in the importance of the consecutive oxidative and non-oxidative dehydrogenation reactions of ethane (both catalytic and thermal) at high temperature and high oxygen content, and for long contact times [14,[19][20][21][22]. It has also been confirmed that the addition of manganese to the catalysts is necessary to obtain better results [3].…”

Section: Resultsmentioning

confidence: 53%

“…Sodium-tungstenmanganese-supported-silica catalyst (with commonly used composition of 2wt.% of Mn and 5wt.% of Na 2 WO 4 ) is one of the most active catalysts that shows good performance and stability over a long period on stream in the OCM process with up to 30% methane conversion and 80% selectivity to ethane and ethene. However, the obtained yield and stability still need to be improved for industrial applications [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Zastosowanie drukowania 3d do modelowania struktury kanałów w monolitycznych katalizatorach dedykowanych dla procesu utleniającego sprzęgania met

2017

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The application of 3d printing in the designing of channel structures in monolithic catalysts dedicated to the oxidative coupling of methane Zastosowanie drukowania 3d do modelowania struktury kanałów w monolitycznych katalizatorach dedykowanych dla procesu utleniającego sprzęgania metanu AbstractIn this work, a new preparation method is proposed to obtain high temperature monolithic structures for catalytic applications. A commercial 3D printer was used to synthesise polymeric templates that were utilised in the designing of channel structures in monolithic catalysts. New materials with manganese and sodium tungstate supported on corundum with macropores of well-defined shapes and sizes were prepared; their catalytic performance was investigated in the process of the oxidative coupling of methane.Keywords: monolithic catalysts, 3D printing, oxidative coupling of methane Streszczenie W niniejszym artykule zaproponowano nową metodę otrzymywania wysokotemperaturowych struktur monolitycznych do zastosowań katalitycznych. Wykorzystano komercyjną drukarkę 3D, aby zsyntezować polimerowe templaty, których użyto do modelowania struktury kanałów w monolitycznych katalizatorach. Przygotowano nowe materiały zawierające mangan i wolframian sodowy na nośniku korundowym, posiadające makropory o dobrze zdefiniowanym kształcie i rozmiarze. Ich właściwości katalityczne zostały zbadane w procesie utleniającego sprzęgania metanu.Słowa kluczowe: katalizatory monolityczne, drukowanie 3D, utleniające sprzęganie metanu 32

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“…One class is based on La 2 O 3 that is doped with alkalineearth metals (Sr, Mg, Ca) [120][121][122][123][124] . The other class is broadly represented as Mn/Na 2 WO 4 /SiO 2 [125][126][127][128][129] . There is also considerable literature on Li/MgO as an OCM catalyst, but these materials are not practically viable because they are unstable under OCM operating conditions [130][131][132][133][134][135][136] .…”

Section: Ocm Catalystsmentioning

confidence: 99%

Process intensification in the catalytic conversion of natural gas to fuels and chemicals

Kee

Karakaya

Zhu

2017

Proceedings of the Combustion Institute

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This paper explores alternative technologies for the conversion of natural gas to higher-value products. Because of methane's chemical stability, all practical processes require elevated temperature (e.g., T > 700 °C) and catalysts to activate the methane. Some approaches are mature and widely practiced at the commercial scale (e.g., steam reforming and Fischer-Tropsch synthesis). Others are emerging, based on laboratory-scale experimentation (e.g., oxidative coupling of methane). In all cases, the present paper is concerned with aspects of process intensification, seeking chemical methods and reactor implementations that can improve overall performance. Performance metrics include reactor size, energy efficiency, conversion rates, and product selectivity. Process intensification approaches include integrated microchannel reactors and heat exchangers as well as a range of permselective membranes.

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Characterization of Mn–Na2WO4/SiO2 and Mn–Na2WO4/MgO catalysts for the oxidative coupling of methane

Cited by 88 publications

References 34 publications

Integrated In Situ Characterization of a Molten Salt Catalyst Surface: Evidence of Sodium Peroxide and Hydroxyl Radical Formation

Integrated In Situ Characterization of a Molten Salt Catalyst Surface: Evidence of Sodium Peroxide and Hydroxyl Radical Formation

Zastosowanie drukowania 3d do modelowania struktury kanałów w monolitycznych katalizatorach dedykowanych dla procesu utleniającego sprzęgania met

Process intensification in the catalytic conversion of natural gas to fuels and chemicals

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