Catalytic Fluorination of Various Chlorinated Hydrocarbons by HF and a Chromium Based Catalyst: Effect of the Presence of Zinc

The Cl/F exchange of chlorinated hydrocarbons with HF was carried out in the gas phase (P = 1 atm. and T = 380 A degrees C) on chromium catalysts doped with zinc. A promoting effect of zinc has been found for various chlorinated hydrocarbons. This positive effect was more significant for CF(3)CH(2)Cl than for CF(3)CHCl(2) or CH(2)Cl(2). CF(3)CH(2)Cl was less reactive than the two other reactants. The promoting effect observed for an atomic ratio Zn/(Zn + Cr) = 0.15 was higher with a low (Zn + Cr) content, which corresponds to a better dispersion of the different elements on the surface. The presence of zinc is supposed to promote the dispersion of chromium and to favour its fluorination to form the centers which are active in Cl/F exchange and were characterized in XPS by energies corresponding to the presence of "CrOF" and "Cr-F" species. Transformation of CF(3)CH(2)Cl (T = 380 A degrees C, CF(3)CH(2)Cl/HF = 1/4) over Zn-promoted Cr/AlF(3) catalysts. Effect of the Zn/(Zn + Cr) atomic ratio and of (Zn + Cr) total amount (figures on the curves) on the activity.