Highly efficient gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane to 1,3,3,3-tetrafluoropropene over mesoporous nano-aluminum fluoride prepared from a polyol mediated sol-gel process

Gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) to 1,3,3,3-tetrafluoropropene (HFO-1234ze), one of the new fourth-generation refrigerants was performed over the mesoporous nano-aluminum fluoride (nano-AlF3) synthesized through a facile polyol mediated sol-gel process. The solvent, molar ratio of HF/Al precursor and calcination temperature during preparation can affect the crystal structures and textural properties, especially the acidity amount of the resulting nano-AlF3. The prepared nano-AlF3 catalysts exhibit the apparent reaction rate among 5.5–7.7 mmol h−1 g−1 with total selectivity above 97% to HFO-1234ze at 280 °C, which are higher than those on conventional β-AlF3 and fluorinated Cr2O3 catalysts. With regard to intrinsic reaction rate and apparent turn over frequency (TOF), β-AlF3 displays the highest activity among the tested catalysts. The characterization results reveal that the density of acid sites of nano-AlF3 is associated with its TOF in this reaction, and reducing the density of acid sites is beneficial to achieving high activity. However, the distribution of cis, trans-isomers for HFO-1234ze is not easily tuned by adjusting the preparation conditions of nano-AlF3. Catalytic stability tests show that nano-AlF3 exhibits almost constant activity over 200 h, which are much more stable than conventional AlF3 and fluorinated Cr2O3 catalysts.