Titanium Niobate and Titanium Tantalate Nanosheets as Strong Solid Acid Catalysts

HTiNbO5, HTi2NbO7, and HTiTaO5 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, Nb2O5·nH2O. NH3 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. 1H magic-angle-spinning nuclear magnetic resonance spectroscopy suggests that bridging hydroxyl groups (Ti(OH)M) (M = Nb5+ or Ta5+)) on these titanium niobate/tantalate nanosheets function as strong Brønsted acid sites that are available for this reaction.