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|Title:||Characterization of CrO<sub>x</sub>-Y<sub>2</sub>O<sub>3</sub> catalysts for fluorination of 2-chloro-1,1,1-trifluoroethane|
|Series/Report no.:||Int. Cl.<sup>8</sup> B01J23/26; B01J37/26; B01J39/10; C07C17/00|
|Abstract:||<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="chmetcnv"> The fluorination of 2-chloro-1,1,1-trifluoroethane (CF<sub>3</sub>CH<sub>2</sub>Cl) to synthesize 1,1,1,2-tetrafluoroethane (CF<sub>3</sub>CH<sub>2</sub>F) has been carried out on various CrO<sub>x</sub>-Y<sub>2</sub>O<sub>3</sub> 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<sub>x</sub> 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<sub>2</sub>O<sub>3</sub> 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<sub>x</sub> content. The highest activity is obtained on a pre-fluorinated catalyst with a Cr loading of 19.5, with a 19 % CF<sub>3</sub>CH<sub>2</sub>Cl conversion at 320 <sup>o</sup>C, corresponding to a formation rate of 2.03 mmol h<sup>-1</sup> g<sup>-1</sup><sub>cat</sub>, which is 3-fold higher than the best result obtained over a Cr/MgF<sub>2</sub> catalyst (0.68 mmol h<sup>-1</sup> g<sup>-1</sup><sub>cat</sub>) under similar conditions. The Cr-Al<sub>2</sub>O<sub>3</sub> 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<sub>2</sub>O<sub>3</sub> catalyst with the same Cr content. The higher activity of Cr-Y<sub>2</sub>O<sub>3</sub> catalyst may be due to the higher degree of dispersion of the Cr(VI) species on the Y<sub>2</sub>O<sub>3</sub> support than on other supports. It is also found that the CrF<sub>x</sub>, CrO<sub>x</sub>F<sub>y</sub> or Cr(OH)<sub>x</sub>F<sub>y</sub> phases originating from higher oxidation state Cr(VI) species are the active sites for the fluorination reaction. </smarttagtype>|
|Appears in Collections:||IJC-A Vol.48A(04) [April 2009]|
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