LIQUID-PHASE OXIDATION OF 1-METHOXY-2-PROPANOL WITH AIR .3. CHEMICAL DEACTIVATION AND OXYGEN POISONING OF PLATINUM CATALYSTS

The deactivation behaviour of carbon and alumina supported platinum catalysts has been studied during the liquid-phase oxidation of 1-methoxy-2-propanol to methoxy-acetone, with air as oxidant. Two different deactivation procedures could be distinguished: deactivation due to strong adsorption of by-products (chemical deactivation) and deactivation which originated from over-oxidation (oxygen poisoning). Among the various parameters which can influence the deactivation behaviour of platinum catalysts, the influence of the nature of the support and of the base have been considered in detail. Both the basic functional groups of activated carbon and the presence of a strong base resulted in similar chemical deactivation. The continuous formation and decomposition of a polymeric carbonyl by-product compound was followed using chromatographic and spectroscopic methods. The decomposition and removal of this by-product from the catalyst surface was favoured by the presence of sufficient oxygen and consequently different response behaviour to a change in oxygen supply was observed for oxygen-poisoned and chemically deactivated catalysts. A comparative study of the oxidation of 2-propanol, 2-butanol and 1-methoxy-2-propanol to the corresponding ketones demonstrated the strong influence of the electron-withdrawing alpha-methoxy group on the deactivation behaviour.