Catalysts For Vapor-Phase Dehydrofluorination Of 1,1,1,3,3-Pentafluoropropane

2,3,3,3-Tetrafluoropropene (HFO-1234yf) and 1,3,3,3-tetrafluoropropene (HFO-1234ze) with low toxicity, low flammability, low global warming potential and zero ozone depletion potential has been considered as a promising candidate for the substitution of 1,1,1,2-tetrafluoroethane (HFC-134a). Due to its outstanding thermodynamic properties, it has been widely used in cooling agents, foaming agents, buffing abrasive agents, displacement drying agents, gaseous dielectrics and power cycle working fluids. In this paper, vapor-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) was conducted to synthesize HFO-1234yf and HFO-1234ze over chromium-based and alumium-based catalysts. The catalysts were characterized by various techniques such as BET, XRD, Raman, H2-TPR, NH3-TPD, TG-DTA and XPS to investigate the phase structures and surface acid properties of the catalysts.The detailed contents of this work are as follows:1. The synthesis of 2,3,3,3-tetrafluoropropene (HFO-1234yf) from 1,1,1,3,3-pentafluoropropane (HFC-245fa) was performed over a series of Ni-Cr2O3 catalysts. It was found that HFC-245fa could be readily dehydrofluorinated to HFO-1234yf and 1,3,3,3-tetrafluoropropene (HFO-1234ze) over these catalysts. Characterization results revealed that the Ni species in the catalysts were mainly metallic. Ammonia temperature-programmed desorption results indicated that the surface acidity was enhanced with increasing Ni contents in the catalysts, which was responsible for the promoted selectivity to HFO-1234yf. It was also found that the formation of carbon during the reaction led to the coverage of surface acidic sites, which accounted for the decrease of the selectivity to HFO-1234yf.2. A series of Pd/AlF3 catalysts were prepared by an impregnation method and tested for vapor-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) to synthesize 1,3,3,3-tetrafluoropropene (HFO-1234ze). The highest activity was obtained on the Pd/A1F3 catalyst containing 1.0 wt.% of Pd, with a HFC-245fa conversion of 79.5% and a HFO-1234ze selectivity of 99.4% after 100 h reaction at 300 ℃. The reactivity was related to the surface acidity, as the AlF3 provided active sites for the reaction. With the addition of Pd, the catalyst stability could be significantly improved. Raman spectroscopic and thermal-gravimetric analysis results revealed that there was less carbon deposit on the spent Pd/AlF3 catalyst surface because the Pd could effectively pyrolyse the carbon deposits. Thus, the Pd/AlF3 catalysts were bi-functional for dehydrofluorination of HFC-245fa.3. Cr2O3 and Al3 catalysts were tested for vapor-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) under the same experiment conditions. It was found that HFC-245fa could be readily dehydrofluorinated to 1,3,3,3-tetrafluoropropene (HFO-1234ze) and 3,3,3-trifluoropropyne (CF3C= CH) over both catalysts at 400 ℃. The reactivity was related to the surface acidity, as AlF3 and Cr2O3 catalysts provided active sites for the reaction. However, HFO-1234yf was only found over Cr2O3 catalyst, which was related to high valent Cr species on the surface of Cr2O3 catalyst.