Heterogeneous catalyzed decomposition reactions of dichlorodifluoromethane in the presence of water on γ-alumina

Article abstract of DOI:10.1016/S0022-1139(96)03515-4

The heterogeneous catalyzed decomposition of CCl₂F₂ (CFC-12) in the presence of water was investigated, employing γ-alumina as catalyst. The catalyzed hydrolysis reaction yields very high conversion degrees of CFC-12 in the first reaction stage. For a period of about 3 h there is a remarkable lack of balance between the amount of liberated HF and HCl owing to the uptake of HF by the oxide solid forming α-AlF₃. Only after about 3 h does the heterogeneous solid/gas reaction come to an end and then the HCl and the HF balance is equal. With the increasing fluoride content of the solid phase, the decomposition degree of CFC-12 decreases to a stable value of about 60% with respect to liberated CO₂. The conversion degree of CFC-12 seems to be higher but this is owing to the formation of CClF₃ (CFC-13), which is nearly stable under the conditions used. Mechanistic explanations are given for the formation of CClF₃ whether by dismutation reactions or owing to hydrofluorination reactions of CFC-12. Arguments are given about which mechanism might be the most probable. Furthermore, mechanistic hypotheses are concluded and discussed with respect to the processes at the catalyst surface on the basis of the experimental results.