gamma-Al2O3 is one of the most active catalysts for hydrolytic decomposition of PFCs but it has been suffered from deactivation. The main reason for the deactivation was the transformation of catalytically active gamma-phase into an inactive alpha-phase by the HF produced during the decomposition of PFCs. To prohibit the phase transformation, structure modifiers such as ZnAl2O4 and AlPO4 were strongly required, which resulted in a remarkable catalyst durability.