Water-assisted oxygen activation during selective oxidation reactions

Tran, Hung-Vu; Doan, Hieu A.; Chandler, Bert D.; Grabow, Lars C.

doi:10.1016/j.coche.2016.08.010

Cited by 21 publications

(18 citation statements)

References 79 publications

(63 reference statements)

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“…The adsorption of H 2 O facilitates the electron transfer from the metal surface to vacuum, which explains why the adsorbed O 2 in the presence of water carries more negative charges than that without water. Furthermore, the dissociation is promoted by hydrogen bonding interaction . This is an interesting, however speculative, approach to explain the improved MAN selectivity in n ‐butane oxidation in the presence of significant amounts of co‐fed H 2 O…”

Section: Resultsmentioning

confidence: 99%

Selective Oxidation of n‐Butane over Vanadium‐Phosphorus Oxide: Oxygen Activation and Dynamics

et al. 2018

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The complex microkinetics of the selective oxidation of n‐butane to maleic anhydride (MAN) over vanadyl pyrophosphate‐based (VPP) catalysts has been widely investigated so far, however, they are still under debate. We present novel results of kinetic analyses and isotope labeling to shed light on the activation of gas‐phase oxygen and the dynamics of oxygen species on the catalyst surface and in the bulk. We suggest the existence of at least two catalytically relevant surface oxygen species responsible for selective and unselective activation of n‐butane, which are formed by adsorption and consecutive dissociation of O2 at the active site. The formation of selective [O] from unselective [O2] is likely promoted by co‐fed H2O, which increases the MAN selectivity. Regarding the VPP bulk serving as a reservoir for active [O] species it is concluded that the dynamic exchange is limited to the amorphous surface layer forming under reaction conditions, whereas the crystalline bulk is not involved into the reaction. Labelling studies are heavily influenced by vital 16O/18O scrambling of MAN isotopes with the reaction product H2O.

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Section: Resultsmentioning

confidence: 99%

Selective Oxidation of n‐Butane over Vanadium‐Phosphorus Oxide: Oxygen Activation and Dynamics

et al. 2018

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“…Despite the extensive research efforts to unravel the mechanism of aqueous-phase aerobic oxidation of simple organic molecules like methanol, ethanol, and formic acid, the role of O 2 in the mechanism remains the subject of vigorous debate. 3,8,9,10 Researchers have invoked the direct participation of adsorbed O* species in catalysis via Langmuir-Hinshelwood recombination with surface-bound organic intermediates. 4,8,11,12 Alternatively, researchers have invoked an indirect role of O 2 in scavenging electrons produced via substrate oxidation.…”

Section: Introductionmentioning

confidence: 99%

“…3,8,9,10 Researchers have invoked the direct participation of adsorbed O* species in catalysis via Langmuir-Hinshelwood recombination with surface-bound organic intermediates. 4,8,11,12 Alternatively, researchers have invoked an indirect role of O 2 in scavenging electrons produced via substrate oxidation. The indirect role of O 2 is supported by isotopic tracer studies, in which oxidations with 18 O 2 show negligible incorporation of the 18 O label in the oxidation products.…”

Section: Introductionmentioning

confidence: 99%

Thermochemical Aerobic Oxidation Catalysis in Water Proceeds via Coupled Electrochemical Half-Reactions

Ryu

Bregante

Howland

et al. 2021

Preprint

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Heterogeneous aqueous-phase aerobic oxidations are an important emerging class of catalytic transformations, particularly for upgrading next generation bio-derived substrates. The mechanism of these reactions and the precise role of O2 in particular remains unclear. Herein, we test the hypothesis that thermochemical aerobic oxidation proceeds via two coupled electrochemical half-reactions for oxygen reduction and substrate oxidation. We collect electrochemical and thermochemical data on common noble metal catalysts under identical reaction/transport environments, and find that the electrochemical polarization curves of the O2 reduction and the substrate oxidation half-reaction closely predict the mixed potential of the catalyst measured in operando during thermochemical catalysis across 13 diverse variables spanning reaction conditions, catalyst composition, reactant identity, and pH. Additionally, we find that driving the oxidation half-reaction reaction electrochemically in the absence of O2 at the mixed potential leads to very similar rates and selectivities as for the thermochemical reaction in all cases examined. These findings strongly indicate that the role of O2 in thermochemical aerobic oxidation is solely as an electron scavenger that provides an incipient electrochemical driving force for substrate oxidation. These studies provide a quantitative and predictive link between thermochemical and electrochemical catalysis, thereby enabling the rational design of new thermochemical liquid-phase aerobic oxidation schemes by applying the principles of electrochemistry.

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“…Despite the extensive research efforts to unravel the mechanism of aqueous-phase aerobic oxidation of simple organic molecules like methanol, ethanol, and formic acid, the role of O2 in the mechanism remains the subject of vigorous debate. 3,8,9,10 Researchers have invoked the direct participation of adsorbed O* species in catalysis via Langmuir-Hinshelwood recombination with surfacebound organic intermediates. 4,8,11,12 Alternatively, researchers have invoked an indirect role of O2 in scavenging electrons produced via substrate oxidation.…”

mentioning

confidence: 99%

“…3,8,9,10 Researchers have invoked the direct participation of adsorbed O* species in catalysis via Langmuir-Hinshelwood recombination with surfacebound organic intermediates. 4,8,11,12 Alternatively, researchers have invoked an indirect role of O2 in scavenging electrons produced via substrate oxidation. The indirect role of O2 is supported by isotopic tracer studies, in which oxidations with 18 O2 show negligible incorporation of the 18 O label in the oxidation products.…”

mentioning

confidence: 99%

Thermochemical Aerobic Oxidation Catalysis in Water Proceeds via Coupled Electrochemical Half-Reactions

Ryu¹,

Bregante²,

Howland³

et al. 2021

Preprint

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<div> Heterogeneous aqueous-phase aerobic oxidations are an important emerging class of catalytic transformations, particularly for upgrading next generation bio-derived substrates. The mechanism of these reactions and the precise role of O2 in particular remains unclear. Herein, we test the hypothesis that thermochemical aerobic oxidation proceeds via two coupled electrochemical half-reactions for oxygen reduction and substrate oxidation. We collect electrochemical and thermochemical data on common noble metal catalysts under identical reaction/transport environments, and find that the electrochemical polarization curves of the O2 reduction and the substrate oxidation half-reaction closely predict the mixed potential of the catalyst measured in operando during thermochemical catalysis across 13 diverse variables spanning reaction conditions, catalyst composition, reactant identity, and pH. Additionally, we find that driving the oxidation half-reaction reaction electrochemically in the absence of O2 at the mixed potential leads to very similar rates and selectivities as for the thermochemical reaction in all cases examined. These findings strongly indicate that the role of O2 in thermochemical aerobic oxidation is solely as an electron scavenger that provides an incipient electrochemical driving force for substrate oxidation. These studies provide a quantitative and predictive link between thermochemical and electrochemical catalysis, thereby enabling the rational design of new thermochemical liquid-phase aerobic oxidation schemes by applying the principles of electrochemistry. </div>

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Water-assisted oxygen activation during selective oxidation reactions

Cited by 21 publications

References 79 publications

Selective Oxidation of n‐Butane over Vanadium‐Phosphorus Oxide: Oxygen Activation and Dynamics

Selective Oxidation of n‐Butane over Vanadium‐Phosphorus Oxide: Oxygen Activation and Dynamics

Thermochemical Aerobic Oxidation Catalysis in Water Proceeds via Coupled Electrochemical Half-Reactions

Thermochemical Aerobic Oxidation Catalysis in Water Proceeds via Coupled Electrochemical Half-Reactions

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