PTFE DISPERSED HYDROPHOBIC CATALYSTS FOR HYDROGEN WATER ISOTOPIC EXCHANGE .2. WATER POISONING

Deuterium exchange between hydrogen and liquid water has been investigated using platinum supported on activated charcoal, alumina and zeolites. The effect of coating the support material with a polytetrafluoroethene (PTFE) film on the 1H-2H exchange activity of different catalysts was investigated in detail. The exchange reaction has been found to follow a two-step process, a predominant fast step followed by a slower one, the faster step being more susceptible to water poisoning. The data suggest that the 1H-2H exchange process proceeds via chemisorption of both the hydrogen and water molecules over metal sites and the energetic heterogeneity of metal sites is responsible for the multi-step exchange behaviour. The water-induced catalytic poisoning was found to be related to the strength of water-substrate bonding and not only on the water condensation or the water adsorption capacity of the support. The presence of a thin porous, polymeric film is capable of minimizing water condensation and lowering the substrate-water interaction, thus helping the catalyst to retain its activity in the presence of liquid water.