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) (CrO3) and Cr(V) (YCrO4) species were easy to fluorinate, and generated CrO2F2 or/and CrOF3, while the Cr(III) (Cr2O3) species was difficult to fluorinate. Moreover, the CrO2F2 and CrOF3 species were stable in the AHF atmosphere, but they easily transform into CrO3 in N2 atmosphere and further decomposed to Cr2O3 at 400 °C. Moreover, Cl/F exchange reaction of CF3CH2Cl to CF3CH2F over these Cr species indicated that the high-oxidation-state CrOxFy (CrO2F2 and CrOF3) species exhibited much higher reactivities than Cr2O3, suggesting that these species (CrO2F2 and CrOF3) may be the active phases of the reaction. Copyright © 2010 John Wiley & Sons, Ltd.