Breakthrough synthesis of 2,3,3,3-tetrafluoropropene via hydrogen-assisted selective dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane over nickel phosphides

Abstract

Herein, we report a hydrogen-assisted selective dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) to 2,3,3,3-tetrafluoropropene (HFO-1234yf) over nickel phosphides (Ni2P, Ni12P5 and Ni3P) catalysts. The Ni3P catalyst exhibited higher activity and HFO-1234yf selectivity than Ni12P5 and Ni2P catalysts. An induction period over Ni3P was observed during the initial 15 h under reaction conditions of 300 °C and H2/HCFC-244bb of 1.5, then a steady HCFC-244bb conversion ~ 42% and HFO-1234yf selectivity ~ 88% was obtained within the rest of 105 h. The catalysts were characterized by in situ temperature-programmed desorption analysis, X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The in situ H2-TPD results reveal that Ni3P was capable of forming larger amount of active hydrogen species than the other nickel phosphides, but by comparing the desorption temperature the reactivity of active hydrogen species on Ni3P was weaker than those formed on Ni12P5 and Ni2P, leading to higher activity and HFO-1234yf selectivity of Ni3P. The theoretical calculations also find that the adsorption energy of H2 over Ni3P is lower than those over Ni12P5 and Ni2P. XPS and TEM-mapping show that a surface chlorination occurred on Ni3P during the initial stage of reaction, resulting in an increase of surface acidity. Thus, the enhanced catalytic efficiency of Ni3P during the induction period can be attributed to a synergism between the metal sites and the in situ formed weak acid sites, further promoting the C-Cl bond scission by active H species and inhibiting the deep-hydrogenation.