Novel tough catalyst supports for reactions involving HF

Metal fluorides are more stable than metals and metal oxides; therefore, no oxides can be applied as catalyst supports for the reactions in which hydrogen fluoride is involved. The authors observed that metal phosphates are not reactive to HF at higher reaction temperatures such as 973 K. Hence, the decomposition of CCIF2CCIF2 was studied over Pt-supported SiO2, Al2O3, and AlPO4-based catalysts. Hydrodehalogenation proceeded and CHF2CCIF2 and C2H6 were formed as major products, small amounts of CHF2CHF2, CH2FCCIF2, CH2FCF3. and CH4 were also formed. Pt/SiO2 was the most active; however, SiO2 reacted with HF and the SiF4 formed sublimated. Following these, Al2O3 was the most active; however, it reacted with HF to form AlF3 and was deactivated. Similar hydrodehalogenation proceeded over Pt/AlPO4 and Pt/ (CePO4-AIPO(4)). The crystal structure of these catalysts did not change during the catalytic reaction, although the reduction of specific surface areas (SSA) was observed. Therefore, AlPO4 and Ce containing AlPO4 are suitable as catalyst supports in reactions in which HF is involved. XPS showed that the electronic effects of AlPO4 lie between that of SiO2 and Al2O3. A good linear relationship is found to exist between the initial reaction rates per unit Surface area of Pt metal supported on the supports and the binding energy of supported Pt. This suggests that the more cationic the Pt. the more easily it could abstract Cl- from CCIF2CCIF2. (c) 2004 Elsevier B.V. All rights reserved.