PROPANE AND PROPENE OXIDATION OVER PLATINUM AND PALLADIUM ON ALUMINA - EFFECTS OF CHLORIDE AND WATER

The oxidation of propane and propene was investigated on palladium and platinum supported catalysts. Catalyst intrinsic activities, evaluated by light-off temperatures in slightly oxidizing reactant mixture (5% excess oxygen), show an optimum particle size which maximizes the catalytic activity for a given metal loading. On catalysts prepared from chloride containing precursor salts, chloride poisons the metallic activity whatever the particle size. Moreover, reaction isotherms under varying oxygen levels point out that the effect of chloride is more detrimental under oxidizing conditions. After successive oxidation cycles, this poisoning effect disappears as a consequence of the removal of chloride from the catalyst surface by water produced during propane and propene combustion. On the other hand, addition of relatively large quantities of water (equivalent to the content of the exhaust gas) inhibits the oxidation of hydrocarbon. Poisoning effects of chloride and water are explained by a decreasing active surface for the reactions under consideration.