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

• HFO-1234yf is obtained by H 2 -assisted dehydrochlorination of HCFC-244bb on NiP x . • Ni 3 P shows similar activity and selectivity to Pd/C, but superior catalytic stability. • Active H species formed by heterolytic cleavage of H 2 serve as the real active site. • A surface chlorination occurred at the initial stage increases the acidity of Ni 3 P. • Synergism between the metal and formed acid sites promotes the formation of HFO-1234yf. 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 (Ni 2 P, Ni 12 P 5 and Ni 3 P) catalysts. The Ni 3 P catalyst exhibited higher activity and HFO-1234yf selectivity than Ni 12 P 5 and Ni 2 P catalysts. An induction period over Ni 3 P was observed during the initial 15 h under reaction conditions of 300 °C and H 2 /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 H 2 -TPD results reveal that Ni 3 P 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 Ni 3 P was weaker than those formed on Ni 12 P 5 and Ni 2 P, leading to higher activity and HFO-1234yf selectivity of Ni 3 P. The theoretical calculations also find that the adsorption energy of H 2 over Ni 3 P is lower than those over Ni 12 P 5 and Ni 2 P. XPS and TEM-mapping show that a surface chlorination occurred on Ni 3 P during the initial stage of reaction, resulting in an increase of surface acidity. Thus, the enhanced catalytic efficiency of Ni 3 P 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.