Noble-metal-catalysed aqueous alcohol oxidation : reaction start-up and catalyst deactivation and reactivation

The influence of the reaction start-up procedure on the oxidation of a polyol, methyl a-D-glucopyranoside, was investigated. Results were obtained from semi-batch experiments with Pt catalysts and molecular oxygen as oxidant. Three types of reaction start-up procedures were applied with respect to the pretreatment of the catalyst slurry: reductive, oxidative, and inert. The experimental results are described by a recently developed dynamic electrochemical kinetic model. The reductive start-up results in the highest initial catalyst activity, compared with the other start-up procedures. It was found that the catalyst needs pretreatment before the reaction is started, as inert start-up resulted in no catalytic activity at all. The formation of inactive platinum oxides (i.e., overoxidation) is the main cause of catalyst deactivation under oxygen-rich conditions, for a weak reducing compound, and is independent of the start-up procedure. It also appeared that the rate of overoxidation is lower in the absence of reaction, which could be modelled with the assumption that overoxidation needs free sites to take place. The mechanism of catalyst deactivation has been verified through intermediate catalyst reactivation. The model adequately describes this reactivation step.