High Ethylene‐Yield Oxidative Dehydrogenation of Ethane Using Sulfur Vapor as a “Soft” Oxidant

Liu, Shanfu; Arinaga, Allison M.; Lohr, Tracy L.; Marks, Tobin J.

doi:10.1002/cctc.202000858

Cited by 6 publications

(7 citation statements)

References 44 publications

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“…However, to our knowledge, this is the first time that O 2 and S 2 have been directly compared for a light alkane partial oxidation reaction. The results support the hypothesis introduced in prior literature that S 2 can afford higher olefin selectivity by moderating the thermodynamic driving force towards overoxidation [5a,6–7] …”

Section: Figuresupporting

confidence: 90%

“…One approach to address this issue that has been explored in the ODHP literature is to replace O 2 with a softer oxidant, such as CO 2 or N 2 O, in order to mitigate the overoxidation to CO x. [4] In addition to oxygen‐containing molecules, this laboratory has previously shown that S 2 can be used as an alternative oxidant in a number of light alkane partial oxidations such as methane coupling to ethylene, [5] the ODH of ethane, [6] and ODHP [7] . For ODHP, we investigated a number of bulk metal sulfide surfaces as catalysts for this sulfur‐ODHP (SODHP) reaction, finding that the activation energy for propylene formation decreases with falling metal‐sulfur bond energy.…”

Section: Figurementioning

confidence: 99%

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Supported Vanadium Catalysts for Selective Sulfur‐Oxidative Dehydrogenation of Propane

et al. 2021

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The catalytic oxidative dehydrogenation of propane (ODHP) is a challenging reaction due to facile competing overoxidation to COx. The gaseous disulfur molecule, S2, is isoelectronic with O2 and has been shown to act as an alternative, “soft oxidant” for the analogous process (SODHP) over bulk metal sulfide catalysts. However, these bulk catalysts suffer from low surface areas and ill‐defined active sites – issues that might be addressed with a supported catalyst. Here we investigate supported V/Al2O3 materials for SODHP. We show that these catalysts are highly selective for propylene, far surpassing the yields of the prior bulk systems. Isolated sulfided vanadium species are found to be more active and selective than crystalline vanadium sulfide. Additionally, we compare the S2 and O2 oxidants over sulfided and calcined V/Al2O3 materials, respectively, and find that the propylene selectivity is enhanced using S2 as the oxidant. These results suggest that sulfur is a promising soft oxidant that can be used to achieve high propylene selectivities over supported metal sulfides.

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Section: Figuresupporting

confidence: 90%

Section: Figurementioning

confidence: 99%

Supported Vanadium Catalysts for Selective Sulfur‐Oxidative Dehydrogenation of Propane

et al. 2021

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“…Catalytic runs begin by exposing the Fe 3 O 4 precatalyst to flowing H 2 S (sulfurization) for several hours to produce the active catalyst. Catalytic experiments flow Ar over molten S 8 (melting point = 388 K; boiling point = 718 K) to transport gaseous S 2 and a CH 4 into the reactor described previously (29,34,41,42). Gaseous products are quantified by gas chromatography.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, the kinetic measurements were conducted below 865 °C. The apparent S 2 and methane rate orders were determined from the changes in methane conversion rate as a function of the S 2 and methane pressures, respectively (41,42). Note these empirical orders are overall apparent orders averaged over the various reaction network pathways (discussed below).…”

Section: Resultsmentioning

confidence: 99%

“Soft” oxidative coupling of methane to ethylene: Mechanistic insights from combined experiment and theory

Liu

Udyavara

Zhang

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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The oxidative coupling of methane to ethylene using gaseous disulfur (2CH4 + S2 → C2H4 + 2H2S) as an oxidant (SOCM) proceeds with promising selectivity. Here, we report detailed experimental and theoretical studies that examine the mechanism for the conversion of CH4 to C2H4 over an Fe3O4-derived FeS2 catalyst achieving a promising ethylene selectivity of 33%. We compare and contrast these results with those for the highly exothermic oxidative coupling of methane (OCM) using O2 (2CH4 + O2 → C2H4 + 2H2O). SOCM kinetic/mechanistic analysis, along with density functional theory results, indicate that ethylene is produced as a primary product of methane activation, proceeding predominantly via CH2 coupling over dimeric S–S moieties that bridge Fe surface sites, and to a lesser degree, on heavily sulfided mononuclear sites. In contrast to and unlike OCM, the overoxidized CS2 by-product forms predominantly via CH4 oxidation, rather than from C2 products, through a series of C–H activation and S-addition steps at adsorbed sulfur sites on the FeS2 surface. The experimental rates for methane conversion are first order in both CH4 and S2, consistent with the involvement of two S sites in the rate-determining methane C–H activation step, with a CD4/CH4 kinetic isotope effect of 1.78. The experimental apparent activation energy for methane conversion is 66 ± 8 kJ/mol, significantly lower than for CH4 oxidative coupling with O2. The computed methane activation barrier, rate orders, and kinetic isotope values are consistent with experiment. All evidence indicates that SOCM proceeds via a very different pathway than that of OCM.

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“…11 Sulfur-containing gases represent another class of alternative oxidants. Previously, this laboratory showed that sulfur vapor, S 2 , can be utilized as an oxidant for various light alkane partial oxidations, including methane coupling, 15−17 ethane ODH, 18 and ODHP. 19,20 Unlike CO 2 −ODHP, SODHP remains exergonic at 500 °C.…”

Section: ■ Introductionmentioning

confidence: 99%

Origin of Rate and Selectivity Trends and Exceptional Yield in Sulfur-Oxidative Propane Dehydrogenation Over Supported Vanadium Catalysts

Arinaga,

Biswas,

Zhang

et al. 2023

ACS Catal.

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Sulfur vapor (S2) is an effective alternative oxidant for propane dehydrogenation, (S)ODHP, with vanadium-based catalysts displaying promising performance and propylene selectivity significantly greater than with O2 as the oxidant (ODHP). However, a deeper mechanistic understanding of SODHP versus ODHP will be necessary for further catalytic performance. Here, we investigate these trends over vanadium catalysts supported by Al2O3, TiO2, ZrO2, and SiO2. First, support effects on V/M x O y -catalyzed SODHP are analyzed, revealing marked support effects on the catalyst reducibility and activity. The result is maximum propylene selectivity and yield of 96 and 41%, respectively, over a sulfided V/SiO2 catalyst, surpassing most metrics in the peer-reviewed ODHP literature. Second, propane overoxidation kinetic pathways for SODHP vs. ODHP are compared, revealing that, contrary to traditional oxide catalytic pathways, secondary oxidation of propylene is disfavored over sulfided surfaces. Density functional theory (DFT) analysis reveals that while the sulfided surfaces have propylene binding energies comparable to those of oxide surfaces, the former has less favorable thermodynamic barriers to deep propylene dehydrogenation pathways than the oxide surfaces. These results suggest more competitive propylene desorption vs. propylene overoxidation on sulfided surfaces leads to higher overall selectivity. Thus, SODHP is a promising catalytic alternative for propane oxidation that rivals the traditional O2-mediated approach.

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High Ethylene‐Yield Oxidative Dehydrogenation of Ethane Using Sulfur Vapor as a “Soft” Oxidant

Cited by 6 publications

References 44 publications

Supported Vanadium Catalysts for Selective Sulfur‐Oxidative Dehydrogenation of Propane

Supported Vanadium Catalysts for Selective Sulfur‐Oxidative Dehydrogenation of Propane

“Soft” oxidative coupling of methane to ethylene: Mechanistic insights from combined experiment and theory

Origin of Rate and Selectivity Trends and Exceptional Yield in Sulfur-Oxidative Propane Dehydrogenation Over Supported Vanadium Catalysts

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