The nature and performance of our patented catalysts, with platinum on carbon and polytetrafluorethylene [ Pt/C/PTFE ] and platinum on styrenedivynilbenzene and polystyrene [Pt/STB/PS], used in a water - hydrogen isotope exchange process are presented. The behaviour of the two catalysts in tritiated water was tested by determining their physical and structural characteristics as well as the catalytic activity before and after immersion in tritiated water. The test results emphasized that the two catalysts are highly active in the hydrogen - water vapor ( H2(g)- H2O(v) ) isotopic exchange and highly stable to tritium radiation. It was discovered that Pt/SDB/PS catalyst proved to be quite unstable in the hydrogen- water vapor - water (H2(g)-H2O(v)-H2O(1)) isotopic exchange, while the Pt/C/PTFE catalyst was highly stable. Thus, the Pt/C/PTFE catalyst was chosen for hydrogen isotope separation by liquid hydrogen cryogenic distillation combined with water -hydrogen isotopic exchange in a demonstration scale plant.