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 V 2 O 5 /MgF 2 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 V 2 O 5 in MgF 2 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 MgF 2 support triggered the transformation of V 2 O 5 to vanadium oxyfluoride (VOF x ) species via the reaction between V 2 O 5 and HF, and such species were responsible for the improved activity as they had much higher turnover frequencies (TOFs) than the MgF 2 (0.762 s −1 v.s. 0.026 s −1 at 320 °C). The kinetic results indicated that the 3.1V 2 O 5 /MgF 2 had much lower activation energy (44.6 ± 1.9 kJ mol −1 ) than the MgF 2 (69.0 ± 0.8 kJ mol −1 ). Accordingly, reaction mechanism on the V 2 O 5 /MgF 2 catalyst was proposed, which included slow dehydrofluorination on MgF 2 and fast dehydrofluorination on the VOF x species.
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