The catalytic rate constants of hydrophobic catalysts developed for the removal of tritium mainly generated in the pressurized heavy water reactors should be measured. A recycle reactor was designed and built for characterizing the long-term behavior of the catalyst performance at the various temperatures and gas velocities. The catalytic rate constants were measured at the apparent gas velocity of 0.5 m/s and the temperature of 60 ℃. The initial catalytic rate constant was 8.44 x 10^-4 mol/g.sec. This value is much greater than that considered in the design of Wolsong Tritium Removal Facility.