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The addition of fluoride ions to aluminum〈III〉 salts or to zeolites in aqueous solutions produces fluoro complexes of the general form [AlFitn](3itn), which have been characterized by 27Al and 19F n.m.r. Each fluoroaluminate complex has distinct 19F chemical shifts, although the 27Al chemical shifts of all of the complexes are approximately the same. The 27Al n.m.r. line width, however, changes as different complexes are formed. Zeolite reacts with aqueous fluoride ion solution at approximately neutral pH. n.m.r., FTi.r. and X-ray powder diffraction measurements suggest that the formation of fluoroaluminate species such as K2NaAlF6 at high fluoride ion concentration inside zeolite is an important dealumination mechanism. |
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