Synthesis of niobium-doped titanate nanotubes as solid acid catalysts

Niobium-doped titanate nanotubes (Nb-TiNTs) with various Nb contents were prepared by hydrothermal treatment of Nb-doped TiO 2 with an aqueous NaOH solution and subsequent proton exchange. Nb-TiNTs effectively catalyzed the Friedel-Crafts alkylation of toluene with benzyl chloride or benzyl alcohol and the activity increased with the Nb content, reaching a maximum at 5%. Furthermore, Nb-TiNTs exhibited much higher catalytic activity than other Nb-containing solid acid catalysts such as Nb 2 O 5 · n H 2 O, Nb-Ti mixed oxides and Nb-Ti nanosheet materials. Fourier transform-infrared (FT-IR) spectroscopy measurements revealed that Nb-TiNTs possess both Lewis and Brønsted acid sites, and the amounts of these acid sites are comparable to those of non-doped TiNTs. The high catalytic performance of Nb-TiNTs is attributable to their higher Brønsted acid strength and to the enhanced accessibility of reactant molecules to acid sites. Niobium-doped titanate nanotubes function as an efficient solid acid catalyst for Friedel-Crafts alkylation of toluene with benzyl chloride or benzyl alcohol. Brønsted acid strength and accessibility of reactant molecules are enhanced by Nb-doping.