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

Several mesoporous TaxW10-x mixed oxides prepared from TaCl5 and WCl6 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 (WO3). The acid strength increased with addition of W for mesoporous TaxW10-x oxides, and mesoporous Ta3W7 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 Ta2O5-WO3, HTaWO6 nanosheets, which were a solid acid obtained by exfoliation and aggregation of layered HTaWO6 with strong Bronsted 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 Ta2O5-WO3 and HTaWO6 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.