Methane Coupling Reaction in an Oxy‐Steam Stream through an OH Radical Pathway by using Supported Alkali Metal Catalysts

Yin, Liang; Li, Zhikao; Nourdine, Mohamed; Shahid, Salman; Takanabe, Kazuhiro

doi:10.1002/cctc.201400018

Cited by 42 publications

(65 citation statements)

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“…These data suggest the involvement of parallel C-H activation routes (Scheme 1) involving pathways in which H-abstraction is mediated by either oxygen species on surfaces or by OH radicals, formed via H 2 O/O 2 equilibration on catalyst surfaces, with specic involvement of Na or K cations. 10 These coupled homogeneous-catalytic sequences are consistent with the kinetic effects of O 2 , CH 4 , and H 2 O on the rates of primary and secondary reactions and with the observed H/D isotope effects. These isotopic data also show that C-H activation is irreversible and kinetically-relevant and that O 2 dissociation is quasi-equilibrated for surface routes, but becomes irreversible as O 2 /H 2 O ratios increase.…”

Section: Oxidative Coupling Of Methane: Selectivity Conferred By Strosupporting

confidence: 77%

Catalytic routes to fuels from C₁and oxygenate molecules

et al. 2017

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This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C-C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges. The hurdles in forming the first C-C bond from C molecules are illustrated by the oxidative coupling of methane, in which surface O-atoms form OH radicals from O and HO molecules. These gaseous OH species act as strong H-abstractors and activate C-H bonds with earlier transition states than oxide surfaces, thus rendering activation rates less sensitive to the weaker C-H bonds in larger alkane products than in CH reactants. Anhydrous carbonylation of dimethyl ether forms a single C-C bond on protons residing within inorganic voids that preferentially stabilize the kinetically-relevant transition state through van der Waals interactions that compensate for the weak CO nucleophile. Similar solvation effects, but by intrapore liquids instead of inorganic hosts, also become evident as alkenes condense within MCM-41 channels containing isolated Ni active sites during dimerization reactions. Intrapore liquids preferentially stabilize transition states for C-C bond formation and product desorption, leading to unprecedented reactivity and site stability at sub-ambient temperatures and to 1-alkene dimer selectivities previously achieved only on organometallic systems with co-catalysts or activators. C homologation selectively forms C and C chains with a specific backbone (isobutane, triptane) on solid acids, because of methylative growth and hydride transfer rates that reflect the stability of their carbenium ion transition states and are unperturbed by side reactions at low temperatures. Aldol condensation of carbonyl compounds and ketonization of carboxylic acids form new C-C bonds concurrently with O-removal. These reactions involve analogous elementary steps and occur on acid-base site pairs on TiO and ZrO catalysts. Condensations are limited by α-H abstraction to form enolates via concerted interactions with predominantly unoccupied acid-base pairs. Ketonization is mediated instead by C-C bond formation between hydroxy-enolates and monodentate carboxylates on site pairs nearly saturated by carboxylates. Both reactions are rendered practical through bifunctional strategies, in which H and a Cu catalyst function scavenge unreactive intermediates, prevent sequential reactions and concomitant deactivation, and remove thermodynamic bottlenecks. Alkanal-alkene Prins condensations on solid acids occur concurrently with alkene dimerization and form molecules with new C-C b...

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Section: Oxidative Coupling Of Methane: Selectivity Conferred By Strosupporting

confidence: 77%

Catalytic routes to fuels from C₁and oxygenate molecules

et al. 2017

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“…This behavior is consistent with the observations by Takanabe and Iglesia on the Mn/Na 2 WO 4 /SiO 2 catalyst and by Liang et al. on the same catalyst without Mn …”

Section: Resultsmentioning

confidence: 99%

Detailed Reaction Mechanisms for the Oxidative Coupling of Methane over La₂O₃/CeO₂ Nanofiber Fabric Catalysts

et al. 2017

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We develop and validate detailed reaction mechanisms to represent the oxidative coupling of methane (OCM) over a La2O3/CeO2 nanofabric catalyst. The reaction mechanism includes 39 reversible gas‐phase reactions and 52 irreversible surface reactions between 22 gas‐phase species and 11 surface species. We use a model‐based interpretation of spatially resolved concentration and temperature profiles measured by using a laboratory‐scale packed‐bed reactor. The reaction mechanisms are validated for inlet feed compositions in the range of 7≤CH4/O2≤11. The results are supported by a reaction pathway analysis that provides insight into the relative contributions of the gas‐phase and surface reactions to form the desired C2+ and the undesired COx products. The results provide new quantitative insights into the complex nature of the OCM chemistry, which can assist practical process and reactor development.

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“…HAT is regarded as the key step in numerous chemical transformations, covering heterogeneous, homogeneous, and enzymatic reactivity, and HAT plays also a major role in the oxidative coupling of methane (OCM) [9][10][11][12][13][14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Thermal hydrogen-atom transfer from methane: A mechanistic exercise

Schwarz

2015

Chemical Physics Letters

110

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Methane Coupling Reaction in an Oxy‐Steam Stream through an OH Radical Pathway by using Supported Alkali Metal Catalysts

Cited by 42 publications

References 42 publications

Catalytic routes to fuels from C₁and oxygenate molecules

Catalytic routes to fuels from C₁and oxygenate molecules

Detailed Reaction Mechanisms for the Oxidative Coupling of Methane over La₂O₃/CeO₂ Nanofiber Fabric Catalysts

Thermal hydrogen-atom transfer from methane: A mechanistic exercise

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Methane Coupling Reaction in an Oxy‐Steam Stream through an OH Radical Pathway by using Supported Alkali Metal Catalysts

Cited by 42 publications

References 42 publications

Catalytic routes to fuels from C1and oxygenate molecules

Catalytic routes to fuels from C1and oxygenate molecules

Detailed Reaction Mechanisms for the Oxidative Coupling of Methane over La2O3/CeO2 Nanofiber Fabric Catalysts

Thermal hydrogen-atom transfer from methane: A mechanistic exercise

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Product

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Catalytic routes to fuels from C₁and oxygenate molecules

Catalytic routes to fuels from C₁and oxygenate molecules

Detailed Reaction Mechanisms for the Oxidative Coupling of Methane over La₂O₃/CeO₂ Nanofiber Fabric Catalysts