Structure and Acid Catalysis of Mesoporous Nb₂O₅·<i>n</i>H₂O

Abstract

Mesoporous Nb 2 O 5 · n H 2 O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250−350 m 2 g −1 and pore volumes of 0.2−0.4 mL g −1, which are larger than that of bulk Nb 2 O 5 · n H 2 O. Fourier transform-infrared (FT-IR) analysis using CO and pyridine as basic probe molecules indicated no significant differences in the acid strength of the Lewis and Brønsted acid sites among mesoporous, supermicroporous, and bulk Nb 2 O 5 · n H 2 O. Mesoporous Nb 2 O 5 · n H 2 O exhibits much higher catalytic activity for the hydrolysis of cellobiose than supermicroporous and bulk Nb 2 O 5 · n H 2 O. However, no significant difference was observed between the activity of bulk and mesoporous Nb 2 O 5 · n H 2 O samples for Friedel−Crafts alkylation. The results suggest that mesopores consisting of hydrophilic niobium oxide are advantageous for hydrophilic reactions, but not hydrophobic reactions.