Direct catalytic epoxidation of ethene over copper and alumina-supported copper

Jayamurthy, M; Hayden, P.; Bhattacharya, Atanu

doi:10.1016/j.jcat.2013.09.007

Cited by 9 publications

(19 citation statements)

References 25 publications

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“…[23][24][25] The corrosion of copper under these conditions is extensive, and the oxide layer continues to grow indefinitely with reaction time. However, oxidized copper was found to exhibit partial-oxidation activity, which is consistent with the recent observations of Jayamurthy et al 18 During the reaction in which partial-oxidation activity was detected from oxidized copper, copper metal was still present in the sample underneath the oxide layer, thus it is possible that the partial-oxidation activity originates from the metal/ oxide interface rather than from the oxides themselves. In order to confirm that the copper oxides exhibit partial oxidation activity, we have examined pure un-supported Cu 2 O and CuO powders in epoxidation.…”

Section: Introductionsupporting

confidence: 90%

“…11,12,15 For instance, in propylene epoxidation Cu 2 O was found to generate acrolein, while CuO gave rise only to total oxidation. 16 Contrary to this belief, a few recent works have implicated Cu(I) as an active species in epoxidation, [17][18][19] although supported or promoted catalysts were investigated in these reports, so it is not certain whether the copper oxides alone are intrinsically active for epoxidation.…”

Section: Introductionmentioning

confidence: 98%

“…A recent work by Jayamurthy et al demonstrated that oxidized copper can in fact epoxidize ethylene with an initial moderate selectivity of 28%, followed by a progressive decrease in selectivity to 1%. 18 Based on ex situ X-ray diffraction measurements, the decrease in selectivity was attributed to oxidation of Cu(I) to Cu(II).…”

Section: Introductionmentioning

confidence: 99%

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The oxidation of copper catalysts during ethylene epoxidation

Greiner

Jones

Johnson

et al. 2015

Phys. Chem. Chem. Phys.

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The oxidation of copper catalysts during ethylene epoxidation was characterized using in situ photoemission spectroscopy and electron microscopy. Gas chromatography, proton-transfer reaction mass spectrometry and electron-ionization mass spectrometry were used to characterize the catalytic properties of the oxidized copper. We find that copper corrodes during epoxidation in a 1 : 1 mixture of oxygen and ethylene. The catalyst corrosion passes through several stages, beginning with the formation of an O-terminated surface, followed by the formation of Cu2O scale and eventually a CuO scale. The oxidized catalyst exhibits measurable activity for ethylene epoxidation, but with a low selectivity of <3%. Tests on pure Cu2O and CuO powders confirm that the oxides intrinsically exhibit partial-oxidation activity. Cu2O was found to form acetaldehyde and ethylene epoxide in roughly equal amounts (1.0% and 1.2% respectively), while CuO was found to form much less ethyl aldehyde than ethylene epoxide (0.1% and 1.0%, respectively). Metallic copper catalysts were examined in extreme dilute-O2 epoxidation conditions to try and keep the catalyst from oxidizing during the reaction. It was found that in feed of 1 part O2 to 2500 parts C2H4 (PO2 = 1.2 × 10(-4) mbar) the copper surface becomes O-terminated. The O-terminated surface was found to exhibit partial-oxidation selectivity similar to that of Cu2O. With increasing O2 concentration (>8/2500) Cu2O forms and eventually covers the surface.

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Section: Introductionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 98%

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The oxidation of copper catalysts during ethylene epoxidation

Greiner

Jones

Johnson

et al. 2015

Phys. Chem. Chem. Phys.

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“…Another example of selective oxidation is alkene epoxidation. [26][27][28] Compared with commercialized Ag-based catalyst, Cu-based catalysts are both efficient and cheap. 29 The active sites of epoxidation reaction are still in debate 30 , and in some experiments, the Cu(I) phase is proposed to be responsible for the activity of selective oxidation.…”

Section: Introductionmentioning

confidence: 99%

Structural Rearrangements of Subnanometer Cu Oxide Clusters Govern Catalytic Oxidation

2020

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Sub-nanometer metal oxide clusters are very important materials, widely used for example in catalysis or electronic devices such as sensors. Hence, it is critical to understand the atomic structures and properties of subnanometer metal oxide clusters under a reactive gas environment, such as O 2. We consider here experimentally-accessible precise-size Cu clusters (Cu 4) supported on partial hydroxylated amorphous alumina and show that such clusters can access, in catalytic conditions at high temperature under a pressure of O 2 , a large ensemble of oxidized structures, representing a large variety of oxygen content, of geometries in link with the support, and of catalytic activities for oxidation reactions, as seen from their reducibilities. A 1 grand canonical basin hopping method based on first-principles energy, reveals an ensemble of 24 configurations for the Cu 4 O x cluster of low free energy, less than 0.8 eV above the global minimum. The low free energy ensemble consists of clusters of different stoichiometries, which are mainly Cu 4 O 3 and Cu 4 O 4 in the temperature range of 200−400 ℃ and under a pressure of 0.5 bar of O 2. The presence of several competitive isomers at each composition implies that cluster fluxionality impacts the phase diagram, which should be ensemble-averaged. In terms of catalytic oxidation activity, Cu 4 O 3 isomers present highly variable O abstraction energy: the most stable isomers are inactive for alkane oxidative dehydrogenation, but isomerization to metastable isomers, that proceed with low barrier, enable to create active configurations with low O abstraction energy. O atoms with lowest anionic character, and thus of more electrophilic nature, present the best oxidation capability. In contrast, all Cu 4 O 4 isomers show a low O abstraction energy and a high potential catalytic activity. This manuscript demonstrates the unique structural and electronic properties of sub-nano Cu oxides clusters and illustrates the critical roles of configuration ensembles and rearrangement to highly reactive metastable cluster isomers in nanocatalysis.

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“…Thus, structure-property correlations can be investigated while a catalyst is in its working state. 21 Industrial redox catalysis typically relies on transition metals, in particular copper, which is used as an active component in catalysts for CO2 reduction, 3,[28][29][30] ethylene epoxidation, 4,5 methanol oxidation 31,32 and the water gas shift reaction. 33,34 However, an atomistic description of the state of copper under redox conditions in these catalysts is still unavailable, although integral spectroscopic data obtained under low-pressure conditions indicates that more than one phase is often present in the active catalyst.…”

Section: Mainmentioning

confidence: 99%

Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM

Huang

Jones²,

Fedorov³

et al. 2021

Preprint

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<div>Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown and assignments of active sites remain speculative. Herein, we present an operando transmission electron microscopy study that interrelates structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, we reveal how the interaction between metal and surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium towards a state controlled by chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structureactivity insights that identify distinct mechanisms for water formation and reveals the means by which the system self-adjusts to changes of the gas phase chemical potential. Density function theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis. <br></div>

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Direct catalytic epoxidation of ethene over copper and alumina-supported copper

Cited by 9 publications

References 25 publications

The oxidation of copper catalysts during ethylene epoxidation

The oxidation of copper catalysts during ethylene epoxidation

Structural Rearrangements of Subnanometer Cu Oxide Clusters Govern Catalytic Oxidation

Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM

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