Decomposition of chlorofluorocarbons over metal phosphate catalysis: II. Origin of the stability of AlPO4 and the location of Ce as a promoter

Abstract Aluminum-phosphate catalysts prepared from aqueous solution of Al(NO 3 ) 3 6H 2 O and H 3 PO 4 in acidic condition are effective for hydrolysis of CCl 2 F 2 . Active species of the AlPO 4 catalysts were studied and it was found that not Al(PO 3 ) 3 but pure AlPO 4 was active. AlPO 4 was amorphous when calcined at 1000°C for 5 h. But a slight crystallization of AlPO 4 took place after the reaction at 400°C for 1000 h. Crystallization of AlPO 4 proceeded only in the presence of both CCl 2 F 2 and water vapor. Replacement of 5–10 at.% of Al in AlPO 4 by Ce increased the catalytic activity without changing the selectivity. The Ce-promoted catalysts were composed of the mixture of AlPO 4 and CePO 4 . The compositions of the catalysts were the same as those of parent liquor in preparation and it was almost uniform in the surface and the bulk. AlPO 4 in the Ce-promoted AlPO 4 catalyst was partially crystallized after the calcination at 1000°C for 5 h.