Characterization of CrO_x-Y₂O₃ catalysts for fluorination of 2-chloro-1,1,1-trifluoroethane

Abstract

<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="chmetcnv"> The fluorination of 2-chloro-1,1,1-trifluoroethane (CF₃CH₂Cl) to synthesize 1,1,1,2-tetrafluoroethane (CF₃CH₂F) has been carried out on various CrO_x-Y₂O₃ catalysts with different Cr loadings. The effect of Cr 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 Cr₂O₃ 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 % CF₃CH₂Cl conversion at 320 ^oC, 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/MgF₂ catalyst (0.68 mmol h^-1 g^-1_cat) under similar conditions. The Cr-Al₂O₃ 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-Y₂O₃ catalyst with the same Cr content. The higher activity of Cr-Y₂O₃ catalyst may be due to the higher degree of dispersion of the Cr(VI) species on the Y₂O₃ support than on other supports. It is also found that the CrF_x, CrO_xF_y or Cr(OH)_xF_y phases originating from higher oxidation state Cr(VI) species are the active sites for the fluorination reaction. </smarttagtype>