Inhibition of gold and platinum catalysts by reactive intermediates produced in the selective oxidation of alcohols in liquid waterElectronic supplementary information (ESI) available. See DOI: 10.1039/c1gc15953d

Solid catalysts containing supported nanoparticles of metals such as Au and Pt are very efficient in the oxidation of alcohols obtained from biorenewable sources under mild conditions. However, these reactions sometimes appear to be inhibited by the products formed during oxidation. In this work, the inhibition of glycerol oxidation with O 2 by the product glyceric acid over supported Au and Pt catalysts at 333 K in water at high pH was explored in detail. Inhibition was not caused by strong adsorption of product carboxylates on the metal catalyst as anticipated but instead by strong adsorption of ketone intermediates and condensation products of ketones. These reactive intermediates, which can be produced from sugars, sugar alcohols or other oxygenated derivatives of biomass, can severely deactivate metal oxidation catalysts. Thus, high concentrations of these ketonic species should be avoided when processing biomass-derived feedstocks under mild conditions in base. Whereas simple carboxylic acids did not affect the rate of alcohol oxidation on Au or Pt catalysts, ketonic species either added to the reactant mixture or produced during the oxidation of carbohydrate-based feedstocks severely deactivated the metal catalysts.