Fluorinated chromia structure

XPS and TEM measurements indicate that after fluorination, zinc and nickel, on the surface of these catalysts is present as ZnF2 or NiF2, respectively and these findings support the idea that the Zn(II) and Ni(II) species on doped fluorinated chromias do not become integrated into the surface structure but are, in fact, distinct phases on the surface. 

Treatment of chromia under flow conditions and at moderate temperatures with a variety of C, CFCs or hydrochlorofluorocarbons (HCFCs) or Cj HFCs is an alternative way of producing a fluorinated chromia surface that is catalytically active [24]. It has the advantage that corrosive reagents such as anhydrous HE are avoided. XPS and X-ray excited Auger electron spectroscopy (XAES) demonstrate clearly the points in the processes where activation occurs formation of amorphous highly fluorinated regions at the surface is indicated. Description of local structure is less easily made, although a... 

In order to mimic the properties of a partially fluorinated working chromia catalyst, several model-compound-based studies using an instrumental surface analysis approach have been reported. Laboratory-prepared CrjOj is treated under carefully chosen conditions with a reagent that leads to incorporation of fluorine and the resulting material analyzed, for example, by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Although of academic interest, such studies relate to models rather than to real catalysts and are probably some distance from describing the real situation. The approach is illustrated with two examples. 

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