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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.