Electron spin resonance allied with spin traps to detect and identify atoms and radicals on Pd-supported catalyst surfaces in solution

Burt, Adam; Emery, Michelle; Maher, John P.; Mile, B.

doi:10.1002/1097-458x(200102)39:2<85::aid-mrc805>3.0.co;2-a

Cited by 7 publications

(5 citation statements)

References 14 publications

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“…Apart from reactions with free radicals, spin traps are also capable of abstracting intermediates adsorbed over metal surfaces, often giving the same paramagnetic spin adducts. 43,44 Structures of spin traps used in this study are shown in Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

“…Magnetic properties of the spin adduct often make it possible to assign the structure of the original short-lived radicals. Apart from reactions with free radicals, spin traps are also capable of abstracting intermediates adsorbed over metal surfaces, often giving the same paramagnetic spin adducts. , Structures of spin traps used in this study are shown in Scheme .…”

Section: Introductionmentioning

confidence: 99%

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Spin Trapping of Au−H Intermediate in the Alcohol Oxidation by Supported and Unsupported Gold Catalysts

et al. 2009

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Electron paramagnetic resonance (EPR) spectroscopy and spin trapping were used to explore the mechanism of alcohol oxidation over gold catalysts. Reaction of secondary alcohols with supported and unsupported gold catalysts (e.g., Au/CeO(2), polymer-incarcerated Au nanoparticles, PPh(3)-protected Au nanoparticles) in the presence of spin traps led to the formation of a hydrogen spin adduct. Using isotope labeling, we confirmed that the hydrogen in the spin adduct originates from the cleavage of the C-H bond in the alcohol molecule. The formation of the hydrogen spin adduct most likely results from the abstraction of hydrogen from the Au surface by a spin trap. These results thus strongly suggest intermediate formation of Au-H species during alcohol oxidation. The role of oxygen in this mechanism is to restore the catalytic activity rather than oxidize alcohol. This was further confirmed by carrying out gold-catalyzed alcohol oxidation in the absence of oxygen, with nitroxides as hydrogen abstractors. The support (e.g., metal oxides) can activate oxygen and act as an H abstractor from the gold surface and hence lead to a faster recovery of the activity. Peroxyl radicals were also observed during alcohol oxidation, consistent with a free-radical autoxidation mechanism. However, this mechanism is likely to be a minor side reaction, which does not lead to the formation of an appreciable amount of oxidation products.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spin Trapping of Au−H Intermediate in the Alcohol Oxidation by Supported and Unsupported Gold Catalysts

et al. 2009

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“…In some instances, the nature of the trapped radical can be identified by the parameters obtainable from the EPR spectrum. 21,22 It is known that spin traps such as DMPO are capable of abstracting intermediates adsorbed over metal surfaces 23 or coordinated to a metal center. 24 EPR-spin trapping technique has been previously employed in order to explore the mechanism of thermal oxidation (70 C) of alcohols over Au-np/CeO 2 catalyst.…”

Section: Introductionmentioning

confidence: 99%

Photoinduced reactivity of Au–H intermediates in alcohol oxidation by gold nanoparticles supported on ceria

et al. 2011

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H-Au-np/CeO 2 species, that are important intermediates in the alcohol oxidation by gold nanoparticles, show a photoinduced reactivity. UV-visible photoexcitation in deaerated conditions causes a hydride transfer from gold to the spin trap DMPO. The photoassisted breaking of the Au-H bond restores the catalyst in its active form. As a consequence, photochemical excitation has a positive effect on the catalytic oxidation of 2-pentanol under anaerobic conditions, demonstrating that light can be used in place of oxygen. This new photocatalytic activity of H-Au-np/CeO 2 species is of general interest in the field of catalysis with gold nanoparticles, since the photoinduced hydride shift from gold surface to organic substrates opens up exciting possibilities to use alcohols for hydrogenation reactions.Scheme 1 Mechanism of alcohol oxidation by supported Au-np.

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“…[10][11][12] In particular, the interactions of free radicals with metal surfaces have so far received limited attention. 13, 14 Yet, some exchange and oxidation reactions involving Au nanoparticles can proceed via radical intermediates; 15,16 gold nanoparticles can also trap radicals to form stable organogold species. 17 In this context, EPR spectroscopy and particularly the spin trapping technique are valuable tools which can provide mechanistic information 18-20 about free radical intermediates formed in the presence of metal nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

Radical intermediates in chloroform reactions over triphenylphosphine-protected Au nanoparticles

2009

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Reactions of chloroform over triphenylphosphine-protected Au nanoparticles have been studied using electron paramagnetic resonance (EPR) spectroscopy and a spin trapping technique. Two competing reactions, abstraction of hydrogen and halogen atoms, were identified. The hydrogen abstraction reaction showed an inverse kinetic isotope effect. Treatment of nanoparticles with oxidizing or reducing reagents made it possible to tune the selectivity of radical formation from halogen to hydrogen (deuterium) abstraction. Treatment with PbO(2) promoted the deuterium abstraction reaction followed by the loss of nanoparticle activity, whereas treatment with NaBH(4) regenerated the nanoparticle activity towards Cl atom abstraction. X-ray photoelectron spectroscopy showed an increased Au:P ratio upon treatment with oxidizing reagents. This is likely due to the oxidation of some phosphine ligands to phosphine oxides which then desorb from the nanoparticle surface.

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Electron spin resonance allied with spin traps to detect and identify atoms and radicals on Pd-supported catalyst surfaces in solution

Cited by 7 publications

References 14 publications

Spin Trapping of Au−H Intermediate in the Alcohol Oxidation by Supported and Unsupported Gold Catalysts

Spin Trapping of Au−H Intermediate in the Alcohol Oxidation by Supported and Unsupported Gold Catalysts

Photoinduced reactivity of Au–H intermediates in alcohol oxidation by gold nanoparticles supported on ceria

Radical intermediates in chloroform reactions over triphenylphosphine-protected Au nanoparticles

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