Determination of the kinetics of the reaction of CCl4 with prefluorided Cr2O3 and evaluation of the active site area

The reaction of CCl4 with prefluorided Cr2O3 has been studied by temperature-programmed and isothermal methods. Temperature-programmed reaction showed that CCl3F and CCl2F2 were produced simultaneously with activation energies of 64.5 and 62.5 kJ mol-1, respectively, for the surface exchange reaction. It also allowed evaluation of the surface fluoride radius, a value of 1.86 Å being obtained which is slightly higher than the literature value of 1.33 Å. Isothermal reaction at 523 and 673 K of CCl4 produced simultancous and instantaneous sharp peaks of CCl3F and CCl2F2. The fluoride ion radius derived from the 523 K experiment was 2.8 Å. suggesting that integration of the peak was terminated prematurely while the value at 673 K was 2.6 Å, suggesting involvement of the subsurface fluorine ions.