Decomposition of chlorofluorocarbons over metal phosphate catalysts III.Reaction path of CCl_2F_2 decomposition over AlPO_4

摘要

Decomposition of CCl_4,CCl_2F_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 550deg 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_2F_2 decomposition.Meso-porous AlPO_4 showed almost the same activity with AlPO_4,but the destruciton of the mese-porous structure brought about a loss of activity at 400deg C.