Selection of activated carbon for the selective hydrogenolysis of CCl2F2 (CFC-12) into CH2F2 (HFC-32) over palladium-supported catalysts

In this study, a selection of the support for palladium in the hydrogenolysis of CCl 2 F 2 into CH 2 F 2 has been made. Activated carbon has been selected because of its inertness against HF and HCl, co-products formed under reaction conditions. Different types of activated carbon have been applied in the investigation. These include peat-based, coconut-shell based, and synthetic carbons, which are either steam or chemically activated. The carbons have been purified by different methods, such as washing with aqueous sodium hydroxide and aqueous hydrochloric acid or boiling in concentrated hydrochloric acid or nitric acid or by immersing the carbon in concentrated hydrofluoric acid. A peat-based, steam-activated carbon resulted in the optimal performance for the palladium catalyst. Before impregnation with the palladium precursor, it is necessary to purify this support by a washing procedure to remove impurities present in this carbon. This procedure consists of washing with aqueous sodium hydroxide, aqueous hydrochloric acid, and water. For characterization of the catalysts several methods have been applied, like X-ray fluorescence, CO-chemisorption, and N 2 -adsorption. The prepared catalyst shows a selectivity of 65–85 mol% for the desired product Ch 2 F 2 at all conversion levels of CCl 2 F 2 . It is observed that when too many impurities are removed, the performance of the catalyst is not as good. Therefore, it is concluded that the impurities play an important role in its performance. This is in harmony with the performance of the catalysts prepared from very pure, synthetic carbons which also do not show a good performance. It is postulated that the impurities play a role as either a promoter or anchoring site, which influences the Pd-dispersion.