SELECTION OF ACTIVATED CARBON FOR THE SELECTIVE HYDROGENOLYSIS OF CCL2F2 (CFC-12) INTO CH2F2 (HFC-32) OVER PALLADIUM-SUPPORTED CATALYSTS

Citation
Ejax. Vandesandt et al., SELECTION OF ACTIVATED CARBON FOR THE SELECTIVE HYDROGENOLYSIS OF CCL2F2 (CFC-12) INTO CH2F2 (HFC-32) OVER PALLADIUM-SUPPORTED CATALYSTS, Applied catalysis. A, General, 173(2), 1998, pp. 161-173
Citations number
34
Categorie Soggetti
Chemistry Physical","Environmental Sciences
ISSN journal
0926860X
Volume
173
Issue
2
Year of publication
1998
Pages
161 - 173
Database
ISI
SICI code
0926-860X(1998)173:2<161:SOACFT>2.0.ZU;2-N
Abstract
In this study, a selection of the support for palladium in the hydroge nolysis of CCl2F2 into CH2F2 has been made. Activated carbon has been selected because of its inertness against HF and HCl, co-products form ed 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 chemical ly activated. The carbons have been purified by different methods, suc h as washing with aqueous sodium hydroxide and aqueous hydrochloric ac id or boiling in concentrated hydrochloric acid or nitric acid or by i mmersing the carbon in concentrated hydrofluoric acid. A peat-based, s team-activated carbon resulted in the optimal performance for the pall adium catalyst. Before impregnation with the palladium precursor, it i s necessary to purify this support by a washing procedure to remove im purities present in this carbon. This procedure consists of washing wi th 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 pre pared catalyst shows a selectivity of 65-85 mol% for the desired produ ct Ch(2)F(2) at all conversion levels of CCl2F2. It is observed that w hen too many impurities are removed, the performance of the catalyst i s not as good. Therefore, it is concluded that the impurities play an important role in its performance. This is in harmony with the perform ance of the catalysts prepared from very pure, synthetic carbons which also do not show a good performance. It is postulated that the impuri ties play a role as either a promoter or anchoring site, which influen ces the Pd-dispersion. (C) 1998 Elsevier Science B.V. All rights reser ved.