Hydrolysis of CF4 over alumina-based binary metal oxide catalysts

Carbon tetrafluoride (CF4), which is the most stable compound in perfluorocarbons (PFCs), was catalytically decomposed by the hydrolysis reaction at mild condition as 850-950 K on alumina-based binary metal oxide catalysts. The catalytic activities for the hydrolysis reaction of CF4 with water on the selected metal-Al oxide catalysts were optimized in terms Of H2O/CF4 ratio, loading amount of metal oxide to alumina and pre-treatment conditions of the catalyst. Then, the decomposition reaction of CF4 in the presence of water was examined at the optimized conditions over a variety of metal oxides supported on Al2O3 The steady state catalytic activities on the binary metal oxide catalysts with 5% metal oxide loading on alumina at the reaction temperatures between 853-953 K were found to decrease in the order of Ga approximate to Zn approximate to Zr > Ni approximate to Cr > Sn approximate to (Al2O3) approximate to Ce approximate to In > B approximate to W > Mg approximate to Mn approximate to Cu > Ge approximate to Pb approximate to Li > Bi > Cd > Tl. More than 90% of the robust CF4 can be decomposed over alumina-based Ga, Zn, Ni, In, Sn, and Zr oxide catalysts. The catalytic activity maintained for more than 18 h. Surface metal fluorides produced on binary metal oxide catalysts by the reaction with HF were hydrolyzed under temperature programmed mode and the products were analyzed by a mass spectrometer. It was clearly demonstrated from the experiments that the amount of released HF was well correlated with the corresponding catalytic activity. Further the amounts of L-acid sites measured by in situ FT-IR studies of adsorbed pyridine on the various binary metal oxides also followed the same order as the catalytic activity. These results suggest that breaking of C-F bond in CF4 molecule by L-acid sites is a rate-limiting step in the hydrolysis reaction of CF4 and resulting surface fluoride is easily hydrolyzed with water. Other physical techniques such as XRD, weight and surface area of samples before and after the CF4 hydrolysis reaction were demonstrated that some of binary oxide catalysts were stable under the reaction conditions, especially Ga-Al and Ni-Al binary oxide catalysts. (C) 2003 Elsevier Science B.V. All rights reserved.