1 tunable gold catalysts for selective hydrocarbon oxidation under mild conditions mathew d. hughes,...
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Tunable Gold Catalysts for Selective Hydrocarbon
Oxidation under Mild Conditions
Mathew D. Hughes, Yi-Jun Xu, Patrick Jenkins, Paul McMorn, Philip Landon1, Dan I. Enache,
Albert F. Carley, Gary A. Attard1, Graham J. Hutchings, Frank King, E. Hugh Stitt, Peter Johnston,
Ken Griffin & Christopher J. Kiely
Nature. 2005, 437, 1132-1135
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Catalytic oxidations of organic molecules
Gallezot, P. et. al. Catal. Today. 1997, 37, 405-418.
Enzymatic oxidation
Free radical auto-oxidations initiated by transit
ion metal cations
Metal ion oxidation of coordinated substrates
such as PdII-catalyzed oxidations of olefins
Oxygen transfer to the organic substrate medi
ated by metaloxo or peroxo complexes
Oxidative dehydrogenation on metal surfaces
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Epoxides
http://www.cem.msu.edu/~reusch/VirtualText/addene2.htm
Ocytochrome P450
O2
epoxides
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Selective oxidation of glycerol to glyceric acid using a gold catalyst
Table 1 Oxidation of glycerol using Au/carbon catalystsa
Hutchings, G. J. et. al. Chem. Commun. 2002, 37, 696-697.
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Direct formation of hydrogen peroxide from H2/O2 using a gold catalyst
Table 2 Formation of H2O2 using Au catalysts
Hutchings, G. J. et. al. Phys. Chem. Chem. Phys. 2003, 5, 1917-1923.
Scheme 2
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Synthesis of Gold Catalyst
graphite + refluxe 30min Au/C
O
H HHAuCl4 4H2O
+Au/C Bi(NO3)3stirred for 3h
Au/C(ml Bi soln)
Bi-doped catalyst
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Effect of solvent on selective oxidation of cyclohexene using Au/C catalyst
+ Au/Cpolar solvent
O2
products + Au/CO2, apolar solvent
H2O2 or TBHPproducts
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Styrene oxidation with molecular oxygen using Au/C catalysts
Alkene Solvent Initiator Gold Conversion
Product Selectivity Cn
(mol%) (wt%) (%) Sel Yield
Toluene TBHP (5) 1.0 12.3 - 22.8 11.9 62.4 97.1 11.9
1,4-Dimethylbenze
ne
TBHP (5) 1.0 34.2 - 13.5 10.5 37.7 61.7 21.1
1,2,4,5- TMB/1,4-
Dimethylbenzene
TBHP (5) 1.0 17.3 - 28.9 15 46.8 90.7 15.7
1,4-Difluorobenzen
e
TBHP (5) 1.0 19.2 - 18.2 9.9 45.8 73.9 14.2
O OCHO
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cis-Stilbene oxidation with molecular oxygen using a 1% Au/C catalyst
Solvent Conversion Selectivity (%) cis:transratio
sel C6 a yield C6
b
(%) cis-Stilbeneoxide
trans-Stilbeneoxide
Toluene 5.5 10.9 65.5 0.17 76.4 4.2
1,4-Dimethylbenzene 18.6 26.9 57.5 0.47 84.4 15.7
Durene/p-Xylene 11.1 38.7 52.3 0.74 91.0 10.1
i-Propylbenzene 47.6 7.1 73.9 0.1 81.0 38.6
t-Butylbenzene 5.8 0 75.8 0 75.8 4.4
1,3,5-tri-i-Propylbenzene
27.6 9.8 55.8 0.18 65.3 18.0
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Cyclohexene oxidation with molecular oxygen using unmodified and Bi-modif
ied Au/C catalysts
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XPS(X-ray photoelectron spectroscopic)
(a) graphite support (b) as prepared Bi-doped 1 wt % Au-graphite catalyst, (c) catalyst after reaction, (d) catalyst in (c) after further reaction with a fresh reactant mixture
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Cyclic voltammograms of 0.5 wt% Au/carbon catalyst
a, Changes in voltammetric response as a function of irreversibly adsorbed Bi. The feature at 0.4–0.5V is associated
with Bi in the first monolayer. Multi-layers of Bi are associated with a stripping peak at 0.2V. Bi loading (mmol): solid
line, 0; dot-dashed, 0.3; dashed, 1.48; dotted, 5.92. b, Loss of multi-layer Bi after reaction as demonstrated by the
attenuation of the Bi stripping peak. The presence of the Bi monolayer feature suggests that some Bi remains on the
catalyst. Solid line, before reaction; dotted line, after reaction.
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cis-Cyclooctene oxidation with molecular oxygen in the absence of a solvent
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Conclusions
• The results show the gold catalyst to have significant potential for selective epoxide formation rather than the c
ompeting allylic oxidation.
• Author anticipate that our finding will initiate attempts to understand more fully the mechanism of oxygen
activation at gold surfaces, which might lead to commercial exploitation of the high redox activity of gold
nanocrystals.