Mechanistic study of C-H bond activation by O on negatively charged Au clusters: α,β-dehydrogenation of 1-methyl-4-piperidone by supported Au catalysts
Au nanoparticles supported on the manganese oxide octahedral molecular sieve OMS-2 can efficiently catalyze α,β-dehydrogenation of β- N -substituted saturated ketones using O 2 as the terminal oxidant. However, despite the utility of this reaction, the active sites and the reaction mechanism remain...
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| Published in | Catalysis science & technology Vol. 11; no. 1; pp. 3333 - 3346 |
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| Main Authors | , , , , , , , |
| Format | Journal Article |
| Published |
25.05.2021
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| Online Access | Get full text |
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| Summary: | Au nanoparticles supported on the manganese oxide octahedral molecular sieve OMS-2 can efficiently catalyze α,β-dehydrogenation of β-
N
-substituted saturated ketones using O
2
as the terminal oxidant. However, despite the utility of this reaction, the active sites and the reaction mechanism remain unclear. Here, the reaction mechanism for the Au/OMS-2-catalyzed aerobic α,β-dehydrogenation of 1-methyl-4-piperidone was investigated mainly by using density functional theory (DFT) calculations. From control experiments under various reaction conditions, we found that O
2
plays an important role in the α,β-dehydrogenation over Au nanoparticles. Thus, we attempted to clarify the mechanism for the α,β-dehydrogenation of 1-methyl-4-piperidone on Au nanoparticle catalysts by DFT calculations using Au cluster models. The reaction was found to cleave the C-H
α
and C-H
β
bonds in that order. An O
2
molecule adsorbed on the negatively charged Au cluster caused by charge transfer from OMS-2 was found to be sufficiently activated to abstract the H
α
atom in the 1-methyl-4-piperidone substrate. This indirect H
α
abstraction by the activated O
2
was energetically more favorable than direct H
α
abstraction by the Au cluster. The subsequent H
β
abstraction was found to be promoted by adsorbed oxygen species (
i.e.
, HOO, OH, and O) formed after the H
α
abstraction. The reaction mechanism proposed in this study provides general insight into the aerobic C-H bond activation by supported Au catalysts.
Aerobic C-H activation by Au/OMS-2 catalyst is driven by charge transfer from OMS-2 to adsorbed O
2
via
Au cluster. |
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| Bibliography: | bond activation by the adsorbed O and OH species, Cartesian coordinates of optimized structures throughout the catalytic cycle, and results of control experiments for the α,β-dehydrogenation of 1-methyl-4-piperidone by the Au/OMS-2, Au/Al models, C-H on the Au bond activation of 1-methyl-4-piperidone in the first C-H bond cleavage step, comparison of calculation settings, definition of the relative potential energies for the second C-H bond cleavage pathways, optimized structures for C-H and Au/C catalysts. See DOI O α Electronic supplementary information (ESI) available: Surface structure of OMS-2, adsorption structures of 1-methyl-4-piperidone and O 2 β 3 10.1039/d1cy00178g 20 |
| ISSN: | 2044-4753 2044-4761 |
| DOI: | 10.1039/d1cy00178g |