Exfoliated titanate, niobate and titanoniobate nanosheets as solid acid catalysts for the liquid-phase dehydration of D-xylose into furfural

HTiNbO5, HTi2NbO7, HNb3O8, H4Nb6O17, and H2Ti3O7 nanosheets obtained by exfoliation of protonated cation-exchangeable layered metal oxides were examined as solid acids for the cyclodehydration of xylose into furfural. The exfoliated-aggregated composites were characterized by powder X-ray diffraction, N-2 gas adsorption, and scanning electron microscopy, and the acid proper-ties were measured by IR spectroscopy of adsorbed pyridine. In general, the materials had much higher catalytic activity than the nonexfoliated acid-exchanged layered materials. The initial catalytic activities of the exfoliated materials tended to increase with the total amount of acid sites (Bronsted + Lewis, B + L). Furfural yields of up to 55% were achieved after 4 h of reaction in a water-toluene solvent mixture under batch operation at 160 degrees C. Most of the materials could be recycled several times without loss of performance. (c) 2006 Elsevier Inc. All rights reserved.