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Characterization of CrO x -Y 2 O 3 catalysts for fluorination of 2-chloro-1,1,1-trifluoroethane

The fluorination of 2-chloro-1,1,1-trifluorocthane (CF 3 CH 2 Cl) to synthesize 1,1,1,2-tetrafluoroethane (CF 3 CH 2 F) has been carried out on various CrO x -Y 2 O 3 catalysts with different Cr loadings. The effect ofCr loading on the catalyst composition and structure has been investigated. X-ray diffraction and Raman results indicate that the CrO x species with high oxidation state (Cr(VI)) are well dispersed on the catalyst surface when the Cr loading was lower than 19.5 %. With increase in Cr loading, crystalline Cr 2 O 3 and polymeric chromate are formed, which inhibit pre-fluorination of the catalysts. The catalysts are stable under the reaction conditions and the catalytic activity is strongly dependant on the pre-fluorinated CrO x content. The highest activity is obtained on a pre-fluorinated catalyst with a Cr loading of 19.5, with a 19 % CF 3 CH 2 Cl conversion at 320 °C, corresponding to a formation rate of 2.03 mmol h -1 g -1 cat , which is 3-fold higher than the best result obtained over a Cr/MgF 2 catalyst (0.68 mmol h -1 g -1 cat ) under similar conditions. The Cr-Al 2 O 3 catalyst has also been prepared and tested for the probe reaction in this study. The activity is lower as compared to that of the Cr-Y 2 O 3 catalyst with the same Cr content. The higher activity of Cr-Y 2 O 3 catalyst may be due to the higher degree of dispersion of the Cr(VI) species on the Y 2 O 3 support than on other supports. It is also found that the CrF x , CrO x F y or Cr(OH) x F y phases originating from higher oxidation state Cr(VI) species are the active sites for the fluorination reaction.