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 -AlF 3 ) 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 -AlF 3 . The prepared nano -AlF 3 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-AlF 3 and fluorinated Cr 2 O 3 catalysts. With regard to intrinsic reaction rate and apparent turn over frequency (TOF), β-AlF 3 displays the highest activity among the tested catalysts. The characterization results reveal that the density of acid sites of nano -AlF 3 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 -AlF 3 . Catalytic stability tests show that nano -AlF 3 exhibits almost constant activity over 200 h, which are much more stable than conventional AlF 3 and fluorinated Cr 2 O 3 catalysts. [ABSTRACT FROM AUTHOR]