Investigation of fluorinated surfaces by means of radio-labelled probe molecules

A comparative study of surface acidity in the amorphous, high surface area solids, aluminium fluoride, magnesium fluoride and magnesium fluoride containing iron(III) or aluminium(III) fluorides

“…It is comparable in its behaviour to that of solid aluminium chlorofluoride, AlCl x F 3 À x , x = 0.05-0.25 [21,22]. This conclusion is supported by the [ 36 Cl]-tracer studies described here, as the behaviour of AlCl x F 3 À x towards [ 36 Cl]-Bu t Cl [15] is very similar to that described above for HS-AlF 3 . Crystalline MgF 2 is not usually considered to be a strong acid; the pure compound is, at best, a weak Lewis acid [23].…”

“…On recording a second series of spectra, similar observations were made, except that the peaks assignable to hydrocarbon species differed from before. Their nearest match was with trans-but-2-ene, which is the expected product from dehydrochlorination of Bu t Cl [15]. Repetition of this procedure with a different sample (CFC3 in Table 1) led to identical results.…”

“…There are similarities in behaviour in all cases; however, due to the sensitivity of the [ 36 Cl] method [15], subtle differences are also apparent.…”

“…The principles behind the Geiger-Müller direct monitoring method as applied to the study of room temperature dehydrochlorination of [ 36 Cl]-labelled Bu t Cl have been described recently [15] as has the procedure for monitoring H 36 Cl adsorption at b-AlF 3 through multiple exposures of H 36 Cl to the solid [9]. Samples of HS-solids to be studied were added to the Pyrex counting cell in vacuo via an evacuable Pyrex dropping ampoule fitted with a high vacuum PTFE/Pyrex stopcock (J.…”

“…Details have been given elsewhere [15] but the central principle involves using the [ 36 Cl]-labelled compounds, Bu t Cl or anhydrous HCl, to observe the formation of strongly or weakly adsorbed (chemically or physically adsorbed) labelled surface species. The distinction between these is made on the basis of whether the [ 36 Cl]-labelled surface species is removed easily or with difficulty under static or dynamic vacuum at room temperature.…”