Structure and catalysis of layered Nb–W oxide constructed by the self-assembly of nanofibers

Treatment of crystalline Nb2O5–WOx fibers with an aqueous solution of oxalic or tartaric acid resulted in the formation of nanosheets with a layered structure in which fibers were self-assembled. The oxalic and tartaric acid-treated oxides had dense layered structures containing mesopores between the layers with mean diameters of 4.6 and 1.9 nm, respectively. These oxides exhibited much higher recyclability as catalysts for the Friedel-Crafts alkylation and acylation of anisole compared to untreated ones. Furthermore, no deactivation was observed in a continuous flow process for the reaction of anisole and benzyl alcohol at least over 87 days’ period in which turnover number = 33,000 was obtained. The improved catalytic performance was ascribed to the formation of layered structure, which was preserved during reactions.