In situ Raman spectroscopy studies on chromium oxide catalyst in an anhydrous hydrogen fluoride atmosphere

摘要

Changes of different chromium oxide species [Cr(VI), Cr(V) and Cr(III)] were investigated using in situ Raman spectroscopy in an anhydrous hydrogen fluoride (AHF) atmosphere. It was found that the Cr(VI) (CrO_3) and Cr(V) (YCrO_4) species were easy to fluorinate, and generated CrO _2F_2 or/and CrOF_3, while the Cr(III) (Cr _2O_3) species was difficult to fluorinate. Moreover, the CrO_2F_2 and CrOF_3 species were stable in the AHF atmosphere, but they easily transform into CrO_3 in N_2 atmosphere and further decomposed to Cr_2O_3 at 400 °C. Moreover, Cl/F exchange reaction of CF_3CH_2Cl to CF _3CH_2F over these Cr species indicated that the high-oxidation-state CrOxFy (CrO_2F_2 and CrOF_3) species exhibited much higher reactivities than Cr _2O_3, suggesting that these species (CrO_2F _2 and CrOF_3) may be the active phases of the reaction.