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

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.