High performance V2O5/MgF2 catalysts for gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane: Support-induced evolution of new active sites

A series of supported V2O5/MgF2 catalysts were prepared and tested for dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) to synthesize 1,3,3,3-tetrafluoropropene (HFO-1234ze). The addition of V2O5 in MgF2 resulted in up to 5-fold increase in HFC-245fa conversion (from 19.2 to 95.2%) and much enhanced catalyst stability. Characterization results revealed that the dehydrofluorination initiated on the MgF2 support triggered the transformation of V2O5 to vanadium oxyfluoride (VOFx) species via the reaction between V2O5 and HF, and such species were responsible for the improved activity as they had much higher turnover frequencies (TOFs) than the MgF2 (0.762 s−1 v.s. 0.026 s−1 at 320 °C). The kinetic results indicated that the 3.1V2O5/MgF2 had much lower activation energy (44.6 ± 1.9 kJ mol−1) than the MgF2 (69.0 ± 0.8 kJ mol−1). Accordingly, reaction mechanism on the V2O5/MgF2 catalyst was proposed, which included slow dehydrofluorination on MgF2 and fast dehydrofluorination on the VOFx species.