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

Aluminum-phosphate catalysts prepared from aqueous solution of AI(NO3)(3)6H(2)O and H3PO4 in acidic condition are effective for hydrolysis of CCl2F2. Active species of the AlPO4 catalysts were studied and it was found that not Al(PO3)(3) but pure AlPO4 was active. AlPO4 was amorphous when calcined at 1000 degrees C for 5 h. But a slight crystallization of AlPO4 took place after the reaction at 400 degrees C for 1000 h. Crystallization of AlPO4 proceeded only in the presence of both CCl2F2 and water vapor. Replacement of 5-10 at.% of Al in AlPO4 by Ce increased the catalytic activity without changing the selectivity. The Ce-promoted catalysts were composed of the mixture of AlPO4 and CePO4. 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. AlPO4 in the Ce-promoted AlPO4 catalyst was partially crystallized after the calcination at 1000 degrees C for 5 h. (C) 2000 Elsevier Science B.V. All rights reserved.