Kinetics and mechanism of ethylene oxidation. Reactions of ethylene and ethylene oxide on a silver catalyst

Kenson, Robert E.; Lapkin, M.

doi:10.1021/j100702a017

Cited by 88 publications

(31 citation statements)

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“…Within this mechanism the common intermediate, an adsorbed oxametallacycle (OMC), can isomerize to EO or acetaldehyde (AcH), which rapidly burns [34,35]. Because the two isomerization pathways are associated with competing elementary steps, the difference between the activation energies of them is often viewed as providing a computationally accessible upper limit of EO selectivity.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of Ethylene on Oxygen Reconstructed Silver Surfaces

et al. 2016

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We report on theoretical and experimental studies of the reactivity of ethylene with oxygen in two well-known oxygen induced surface reconstructions on silver, the p(2x1) reconstruction on the Ag(110) and the p(4x4) reconstruction on the Ag(111) surfaces. Density functional theory calculations demonstrate that ethylene can react with oxygen on both surfaces to form an oxametallacycle that can decompose into either ethylene oxide or a CO 2 precursor, acetaldehyde.The activation energy associated with acetaldehyde formation is predicted to be 0.4 eV lower than that associated with epoxide formation on both surfaces, though we find lower barriers for all elementary steps on the p(4x4) reconstruction due to its unique structural dynamics. Our calculations predict these dynamics make the p(4x4) reconstruction active in acetaldehyde formation at room temperature. Experiments performed by exposing the p(4x4) reconstruction to ethylene at room temperature support this finding with CO 2 the only carbonaceous product formed during temperature programed desorption. Our results unambiguously demonstrate that, alone, these oxygen reconstructions are not selective in ethylene epoxidation on silver.

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Section: Introductionmentioning

confidence: 99%

Oxidation of Ethylene on Oxygen Reconstructed Silver Surfaces

et al. 2016

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“…170°C. 1 h, 6196 (1 : 1sauredimethylester (10) [7] Addukt) [7] ~ 170"C, 1 h, k. R. (1)-(5) ahnlich wie 4-Phenyl-1,2,4-triazolin-3,5-dion (6) (Tabelle 1); das Cyclophan (2) bildet selbst rnit Acetylendicarbonsauredimethylester (10) (der ca. 106mal weniger reaktiv als (6) ist"]) das I : l-Addukt['].…”

Section: -Phenylunclassified

Acetaldehyd als Hauptprodukt der Oxidation von Ethylenoxid an einem Silberkontakt

Prauser

Dialer

Fischer³

1980

Angew. Chem.

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Falsche Schlüsse über die Relevanz einer Teilreaktion bei heterogenkatalytischen Umsetzungen können gezogen werden, wenn man diese Teilreaktion für sich allein kinetisch untersucht. So wird Ethylen an einem unmodifizierten Ag‐Katalysator zu Ethylenoxid oxidiert, das zu CO2 und H2O „nachverbrennen”︁ kann. Ethylenoxid – unter den gleichen Bedingungen getrennt untersucht – isomerisiert dagegen zu Acetaldehyd. Offenbar blockiert Ethylen die dafür erforderlichen Zentren des Katalysators.

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“…The epoxidation reaction is catalyzed by an α-Al 2 O 3 -supported Ag-based catalyst under high pressure (10–30 bar) and high temperature (200–300 °C) conditions 5 , a process that accomplishes high selectivity for EO in the face of the competing full oxidation of C 2 H 4 to CO 2 . However, accomplishment of C 2 H 4 epoxidation at moderate pressures and temperatures is desirable 6 , 7 from the point of view of reducing heat energy input, enhancing energy efficiency, mitigating thermal damage and deactivation of the catalyst, and further enhancing EO selectivity by reducing high-temperature-favored processes such as isomerization of EO to acetaldehyde 8 and full oxidation to CO 2 . Recently, visible-light photoexcitation of plasmon-resonant Ag nanoparticles (NPs) has been shown to be effective at achieving C 2 H 4 epoxidation at less elevated temperatures and pressures 6 , 7 , 9 .…”

Section: Introductionmentioning

confidence: 99%

In situ formation of catalytically active graphene in ethylene photo-epoxidation

et al. 2018

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Ethylene epoxidation is used to produce 2 × 107 ton per year of ethylene oxide, a major feedstock for commodity chemicals and plastics. While high pressures and temperatures are required for the reaction, plasmonic photoexcitation of the Ag catalyst enables epoxidation at near-ambient conditions. Here, we use surface-enhanced Raman scattering to monitor the plasmon excitation-assisted reaction on individual sites of a Ag nanoparticle catalyst. We uncover an unconventional mechanism, wherein the primary step is the photosynthesis of graphene on the Ag surface. Epoxidation of ethylene is then promoted by this photogenerated graphene. Density functional theory simulations point to edge defects on the graphene as the sites for epoxidation. Guided by this insight, we synthesize a composite graphene/Ag/α-Al2O3 catalyst, which accomplishes ethylene photo-epoxidation under ambient conditions at which the conventional Ag/α-Al2O3 catalyst shows negligible activity. Our finding of in situ photogeneration of catalytically active graphene may apply to other photocatalytic hydrocarbon transformations.

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Kinetics and mechanism of ethylene oxidation. Reactions of ethylene and ethylene oxide on a silver catalyst

Cited by 88 publications

References 0 publications

Oxidation of Ethylene on Oxygen Reconstructed Silver Surfaces

Oxidation of Ethylene on Oxygen Reconstructed Silver Surfaces

Acetaldehyd als Hauptprodukt der Oxidation von Ethylenoxid an einem Silberkontakt

In situ formation of catalytically active graphene in ethylene photo-epoxidation

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