Decomposition of chlorofluorocarbons over metal phosphate catalysts: III. Reaction path of CCl2F2 decomposition over AlPO4

Abstract Decomposition of CCl 4 , CCl 2 F 2 , CClF 3 , and CF 4 was studied in the presence of water vapor over AlPO 4 . They began to decompose at about 300, 330, 450, and 550°C, respectively. A good linear relationship between the reactivity of CFCs and the bond dissociation energy of the C–Cl bond suggests that the C–Cl bond cleavage is the rate-determining step. The lattice structure of AlPO 4 before reaction was slightly distorted but the environment of Al and P ions became uniform after the reaction, consistent with a slight progress of crystallization of AlPO 4 . Supporting AlPO 4 onto active charcoal is not preferable to the support because of its reactivity to water vapor. ALPO-5 was less active than that AlPO 4 because the inside of the pores of ALPO-5 is hydrophobic and not effective for the CCl 2 F 2 decomposition. Meso-porous AlPO 4 showed almost the same activity with AlPO 4 , but the destruction of the meso-porous structure brought about a loss of activity at 400°C.