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

Conte, Marco; Miyamura, Hiroyuki; Kobayashi, Shū; Chechik, Victor

doi:10.1021/ja809883c

Cited by 236 publications

(179 citation statements)

References 82 publications

(111 reference statements)

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“…The gold cations in Au/CeO 2 (rod)-CN do not show any activity. It has been put forward that C-H bond cleavage at the gold surface is the rate limiting step in alcohol oxidation [78,79]. Another important step is the proton abstraction from the alcohol group.…”

Section: Discussionmentioning

confidence: 99%

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

et al. 2011

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The interaction of gold atoms with CeO 2 nanocrystals having rod and cube shapes has been examined by cyanide leaching, TEM, TPR, CO IR and X-ray absorption spectroscopy. After deposition-precipitation and calcination of gold, these surfaces contain gold nanoparticles in the range 2-6 nm. For the ceria nanorods, a substantial amount of gold is present as cations that replace Ce ions in the surface as follows from their first and second coordination shells of oxygen and cerium by EXAFS analysis. These cations are stable against cyanide leaching in contrast to gold nanoparticles. Upon reduction the isolated Au atoms form finely dispersed metal clusters with a high activity in CO oxidation, the WGS reaction and 1,3-butadiene hydrogenation. By analogy with the very low activity of reduced gold nanoparticles on ceria nanocubes exposing the {100} surface plane, it is inferred that the gold nanoparticles on the ceria nanorod surface also have a low activity in such reactions. Although the finely dispersed Au clusters are thermally stable up to quite high temperature in line with earlier findings (Y. Guan and E. J. M. Hensen, Phys Chem Chem Phys 11:9578, 2009), the presence of gold nanoparticles results in their more facile agglomeration, especially in the presence of water (e.g., WGS conditions). For liquid phase alcohol oxidation, metallic gold nanoparticles are the active sites. In the absence of a base, the O-H bond cleavage appears to be rate limiting, while this shifts to C-H bond activation after addition of NaOH. In the latter case, the gold nanoparticles on the surface of ceria nanocubes are much more active than those on the surface of nanorod ceria.

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Section: Discussionmentioning

confidence: 99%

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

et al. 2011

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“…The mechanism illustrates that when the catalyst surface was irradiated by visible light, it can excite the gold nanoparticles on the surface of catalysts, making the activated gold nanoparticles adsorb the H atoms in the OH group of the benzyl alcohol and form Au´H [33]. Thus, the charge of each atom in the benzyl alcohol molecules has changed.…”

Section: Reaction Mechanismmentioning

confidence: 99%

Selective Aerobic Oxidation of Benzyl Alcohol Driven by Visible Light on Gold Nanoparticles Supported on Hydrotalcite Modified by Nickel Ion

et al. 2016

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A series of hydrotalcite (HT) and hydrotalcite modified by the transition metal ion Ni(II) was prepared with a modified coprecipitation method before being loaded with gold nanoparticles. The gold supported on Ni 3 Al hydrotalcite with a Ni 2+ /Al 3+ molar ratio of 3:1 was investigated. Different techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflection spectrum (UV-vis DRS) were applied to characterize the catalysts. A single-phase catalyst with high crystallinity, a layered structure and good composition was successfully fabricated. Good conversions and superior selectivities in the oxidation of benzyl alcohol and its derivatives were obtained with visible light due to the effect of localized surface plasmon resonance (LSPR) of gold nanoparticles and the synergy of the transition metal ion Ni(II). This reaction was proven to be photocatalytic by varying the intensity and wavelength of the visible light. The catalyst can be recycled three times. A corresponding photocatalytic mechanism of the oxidation reaction of benzyl alcohol was proposed.

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“…The result of this addition, known as spin adduct, is a persistent free nitroxide radical with a sufficiently long lifetime to enable detection by conventional EPR spectroscopy [47]. Hyperfine coupling constants between the unpaired electron in the spin adduct and the hydrogen in the beta position of DMPO (Fig.…”

Section: Epr Spin Trapping For the Chhp Decomposition By Fresh And Thmentioning

confidence: 99%

Insights into the Reaction Mechanism of Cyclohexane Oxidation Catalysed by Molybdenum Blue Nanorings

et al. 2015

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Molybdenum blue (MB), is a polyoxometalate with a nanoring structure comprising Mo 5+ -OMo 6+ bridges, which is active for the catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone. However, little is known about the mechanistic features responsible of this catalytic activity. In the present work, the Mo 5+ -O-Mo 6+ moieties embedded in the MB nanoring structure were characterized using diffuse reflectance-UV-Visible spectroscopy and solid state EPR spectroscopy. The amount of Mo 5+ centres was then varied by thermal treatment of the polyoxometalate in the absence of oxygen, and the resultant effect on the catalytic activity was investigated. It was observed that, an increased amount of Mo 5+ centres preserved the conversion of cyclohexane (ca. 6%) but led to a loss of selectivity to cyclohexanol giving cyclohexanone as the major product, and the simultaneous formation of adipic acid. To rationalise these results the catalysts were studied using EPR spin trapping to investigate the decomposition of cyclohexyl hydroperoxide (CHHP), a key intermediate in the oxidation process of cyclohexane. This analysis showed that CHHP has to be bound to the MB surface in order to explain its catalytic activity and product distribution.

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

Cited by 236 publications

References 82 publications

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

Selective Aerobic Oxidation of Benzyl Alcohol Driven by Visible Light on Gold Nanoparticles Supported on Hydrotalcite Modified by Nickel Ion

Insights into the Reaction Mechanism of Cyclohexane Oxidation Catalysed by Molybdenum Blue Nanorings

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