Water improved the durability of titania silica (TiO2/SiO2), phosphate supported zirconia (PO4/ZrO2), and boron phosphate (BPO4) catalysts in decomposing dichlorodifluoromethane (Freon 12). Although configuration changes of TiO2/SiO2 and of PO4/ZrO4 occurred after about 30 h, BPO4 retained its activity without any configuration change even after 35 h. Water eliminated inorganic fluorides accumulated on the surface of BPO4 presumably in the form of hydrogen fluoride. Methanol exhibited little reactivating effect on BPO4. Two catalyst beds were used in a series, and methanol was completely decomposed on Co3O4 in the first bed at 275 degrees C, at which Freon 12 did not decompose much. When the remaining Freon 12 was decomposed over BPO4 in the second bed, the life of BPO4 was prolonged remarkably due to the water produced from methanol in the first bed. Thus only water was effective as a reactivating reagent, and hydrogen atoms of methanol did not work directly.