Gold-Based Catalysts - Transition Metal Catalysis in Aerobic Alcohol Oxidation - page 138

d n 4 r 4 n g | 3

Scheme 5.1 Aldehydes, ketones and carboxylic acids from the aerobic oxidation of
alcohols with gold-based catalysis.

catalyst-to-substrate ratio. All these factors dramatically affect the yield, se-
lectivity and productivity while making dicult to compare different litera-
ture data and to draw general conclusions.
Several research groups around the world have made notable achieve-
ments in this huge field, as detailed throughout this chapter, but Rossi's,
Hutchings' and Corma's studies deserve particular mention. Rossi and co-
workers were the first to discover the catalytic effectiveness of gold in the
liquid-phase oxidation of the C-OH functional group. 5,11,12,31 They even
found how to address the synthesis with preference for carbonylic deriva-
tives, when conducting the oxidation of alcohols in the gaseous phase, or to
carboxylic acids or esters in the liquid phase under mild conditions in the
presence of alkali. The strict synergistic effect between gold nanoparticles
and the supporting material, mainly nanometric CeO 2 , was particularly
emphasized by Corma and co-workers, 78 whereas the bimetallic Au-Pd
catalysts synthesized by Hutchings's group highlighted the synergistic effect
between the two metals, dramatically enhancing the catalytic performances
of the individual metals. 79
Recently, Fan's group carried out the selective oxidation of alcohols to
aldehydes/ketones with O 2 over a series of supported gold catalysts, con-
firming that the catalytic performance strongly depends on either the sup-
port or the preparation method. 51 Among them, Au/CuO catalyst prepared by
coprecipitation was particularly active and selective for the oxidation of
benzylic, cyclic and unsaturated alcohols to the corresponding aldehydes or
ketones by molecular oxygen at atmospheric pressure. Cyclooctanol and
cyclododecanol were oxidized to ketones with notable conversion and se-
lectivity higher than 99%. Regarding the catalyst stability, Au/CuO could be
recycled for use after regeneration. The addition of alkali metal salts to
the reaction mixture did not increase the activity but turned out to improve
the catalytic stability.

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