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

Decomposition of CCl4, CCl2F2, CClF3, and CF4 was studied in the presence of water vapor over AlPO4. 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 AlPO4 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 AlPO4. Supporting AlPO4 onto active charcoal is not preferable to the support because of its reactivity to water vapor. ALPO-5 was less active than that AlPO4 because the inside of the pores of ALPO-5 is hydrophobic and not effective for the CCl2F2 decomposition. Meso-porous AlPO4 showed almost the same activity with AlPO4, but the destruction of the meso-porous structure brought about a loss of activity at 400°C.