Highly Selective Dehydrochlorination of 1,1,1,2-Tetrafluoro-2-chloropropane to 2,3,3,3-Tetrafluoropropene over Alkali Metal Fluoride Modified MgO Catalysts

Gas-phase selective dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) to 2,3,3,3-tetrafluoropropene was investigated over various K and Cs halides modified MgO catalysts. The reaction proceeded in the absence of additives such as air and HF. High dehydrochlorination selectivity (>97%) with moderate activity (>14 mu molh(-1)m(-2)) was achieved on KF and CsF modified MgO catalysts, in which the dehydrofluorination process was inhibited. Compared with alkali metal modified MgO, the dehydrofluorination product, 2-chloro-3,3,3-trifluoropropene increased over Zr and Al modified MgO and fluorinated MgO catalysts (sel. of 20-76 %). XRD and energy-dispersive-spectrometry results revealed that surface chlorination and fluorination occurred on the MgO-based catalysts during the reaction. Introducing alkali metal fluorides into the catalyst can reduce the fluorination of MgO and the deposition of chlorine species, thus improving the dehydrochlorination activity and stability of MgO. The NH3 temperature-programmed desorption (TPD) results show that decreasing the surface acidity of catalyst benefits the dehydrochlorination of HCFC-244bb, whereas the relationship between the basicity of the catalyst and its dehydrohalogenation behavior is complicated as shown by the CO2 TPD results. According to the hard-soft acid-base principle, the dehydrohalogenation selectivity can be correlated with the surface chemical hardness of the catalyst.