Synthesis and Characterization of Mesoporous Ta−W Oxides as Strong Solid Acid Catalysts

Several mesoporous Ta x W 10− x mixed oxides prepared from TaCl 5 and WCl 6 in the presence of poly block copolymer surfactant Pluronic P-123 were examined as potential solid acid catalysts. Amorphous wormhole-type mesopores were observed in samples with x values from 3 to 10, whereas W-rich samples ( x = 0−2) formed nonmesoporous structures with crystallized tungsten oxide (WO 3 ). The acid strength increased with addition of W for mesoporous Ta x W 10− x oxides, and mesoporous Ta 3 W 7 oxide exhibited the highest acid catalytic activity for the Friedel−Crafts alkylation of anisole and the hydrolysis of disaccharides. The results are compared with those of nonporous Ta 2 O 5 −WO 3, HTaWO 6 nanosheets, which were a solid acid obtained by exfoliation and aggregation of layered HTaWO 6 with strong Brønsted acid sites in the interlayer, and a range of conventional solid acid catalysts. Mesoporous Ta−W oxides exhibited a turnover rate higher than that of nonporous Ta 2 O 5 −WO 3 and HTaWO 6 nanosheets, indicating that the mesoporous structure is an advantageous environment for the strong acid sites, because of the high surface area and easy reactant accessibility.