Chromia isotopic exchange

M. Tinkle, J. A. Dumesic, Isotopic exchange measurements of the rates of adsorption/desorp-tion and inter conversion of CO and CO2 over chromia-promoted magnetite implications for water-gas shift, J. Catal. 103 (1987) 65-78. 

Direct evidence for a combination of catalytic fluorination and chlorination [4] was obtained from radiotracer studies in which fluorinated chromia catalysts were labelled with the short-lived (t /2 = 110 min) / + emitting isotope fluorine-18 [11]. Using this isotope it was possible to probe the interactions between HF and various fluorinated chromia catalysts more directly than had been possible hitherto. Three types of surface F-containing species were differentiated, weakly adsorbed HF which was easily removed by an inert gas flow, non-labile F, believed to be bound directly to surface Crin, and catalytically active F which could be incorporated into the organic products [12]. The controversy between dismutation (concerted F-for-Cl and Cl-for-F transfers) and non-concerted halogen exchange processes has been resolved more recently and the evidence is described later in the chapter. What is clear from this early work however, is the importance of aluminium and chromium(III) oxides as catalyst precursors. Fluorination of the surfaces of these oxides is slow (cf [12]) and although there are many references to alu-... 

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