Two-dimensional metal oxide sheets in HTiNbO(5) and HSr(2)Nb(3)O(10), cation-exchangeable layered metal oxides, were examined as solid acid catalysts. Exfoliation of HTiNbO(5) and HSr(2)Nb(3)O(10) in aqueous solutions formed colloidal single-crystal TiNbO(5)(-) and Sr(2)Nb(3)O(10)(-) nanosheets, which precipitated under an acidic condition to form aggregates of HTiNbO(5) nanosheets and HSr(2)Nb(3)O(10) nanosheets. Although esterification of acetic acid, cracking of cumene, and dehydration of 2-propanol were not catalyzed by original HTiNbO(5) because of the narrow interlayer distance, which prevents the insertion of organic molecules, HTiNbO(5) nanosheets functioned as a strong solid acid catalyst for the reactions. Nanosheets of HSr(2)Nb(3)O(10) exhibited no or slight catalytic activity for these reactions. NH(3) temperature-programmed desorption and (1)H magic-angle spinning nuclear magnetic resonance spectroscopy revealed that HTiNbO(5) nanosheets have strong Brønsted acid sites, whereas HSr(2)Nb(3)O(10) nanosheets do not.

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HTiNbO 5 , HTi 2 NbO 7 , and HTiTaO 5 nanosheets obtained by exfoliation of protonated cation-exchangeable layered metal oxides are examined as solid acids. These nanosheets exhibit high catalytic activity for esterification of acetic acid and hydrolysis of ethyl acetate, competing with niobic acid, Nb 2 O 5 ‚nH 2 O. NH 3 temperature-programmed desorption reveals that the acidity of the nanosheets corresponds to the density of strong acid sites of H-ZSM-5 or niobic acid. 1 H magic-angle-spinning nuclear magnetic resonance spectroscopy suggests that bridging hydroxyl groups (Ti(OH)M) (M ) Nb 5+ or Ta 5+ )) on these titanium niobate/tantalate nanosheets function as strong Brønsted acid sites that are available for this reaction.