Catalytic fluorination over chromium oxides. Preparation of Hydrofluorocarbons

Effects of M-promoter (M=Y, Co, La, Zn) on Cr2O3 catalysts for fluorination of perchloroethylene

“…5b), only four Raman bands at 302 (a 1 ), 350 (a 2 ), 550 (a 3 ) and 610 cm À1 (a 4 ) were observed, indicating that the crystalline Cr 2 O 3 is difficult to be fluorinated in HF atmosphere, which is consistent with the XRD results. Besides, for the M-Cr 2 O 3 (F) catalysts, the b and g bands corresponding to polymeric chromate and Cr(VI) species disappeared, indicating that these high valent Cr species could be easily fluorinated, which is consistent with the results reported in literatures [26]. Compared with the Co-Cr 2 O 3 catalyst, the Raman band at 691 cm À1 disappeared for the Co-Cr 2 O 3 (F) catalyst, which indicates that Co 3 O 4 transforms into Co fluoride.…”

“…In addition, Quan et al [24] found that Cr species with higher oxidation state shows higher catalytic activity than Cr(III). Besides, it was found that the catalyst activity also strongly depended on the surface acidity of the catalysts [25,26].…”

Characterization and Performance of CrO<SUB><EM>x</EM></SUB>-Y<SUB>2</SUB>O<SUB>3</SUB> Catalysts for the Synthesis of 1,1,1,2-Tetrafluoroethane

“…Inourpreviouswork [17] ,wefoundthattheCrYFcatalystscan holdgoodstability(72h).Therefore,theCrYFScatalysts,which wereusedforcharacterization,canprovideeffectiveinformation onthestructureoftheusedcatalysts. TheBETsurfaceareasofthefreshandusedcatalystsare showninTable1.Forthefreshcatalysts(CrYO),thesurface areavariesfrom11to24m 2 • g -1 ,withtheCrYO鄄Npossessing thehighestsurfacearea.Fortheusedcatalysts(CrYFS),thesur-faceareasareabout60m 2 • g -1 ,whicharehigherthanthoseof thecorrespondingfreshcatalysts.Thisindicatesthatthereisa structuralchangeoftheCrYOcatalystsduringthefluorination asclaimedpreviously [17] .Itwasfoundthatfortheconventional chromiumorCr鄄Alsystem,therewasadramaticdecreaseinthe BET鄄areaafterfluorination [19][20][21] [13] ,theCrYFS catalystsamplescontainanhydrousorlesshydratedamorphous CrF 3 specieswhichmightundergoslowhydrationreactionto givecrystallineCrF 3 •3H 2 Owhencontactedwithatmospheric H 2 O.Moreover,adetailedanalysisofthephaseandphasecom-positionofCrYFScatalystsareshowninTable1.FromTable1, itcanbeseenthattherelativepercentagecontentofcrystalline CrF 3 •3H 2 OincreasedintheorderofCrYFS 鄄 H<CrYFS 鄄 Cl< CrYFS鄄N.ThephasecompositionsoftheCrYFS鄄N,CrYFS鄄Cl, andCrYFS鄄Hcatalystswere14.3%,10.8%,and6.8%(w),respectively.…”