Activity and acidity of Nb2O5-MoO3 and Nb2O5-WO3 in the Friedel-Crafts alkylation

Nb2O5 loaded on the supports and mixed with oxides was studied to investigate the activity and acidity for Friedel-Crafts benzylation of anisole. From the study on the loaded catalysts, a preliminary conclusion for the selection of metal oxide was obtained; namely, such an acidic oxide as silica was suitable for the support of Nb2O5. Then, MoO3 and WO3 were mixed with Nb2O5, and prominent high catalytic activity and acidities were observed. Both oxides of Nb2O5-MoO3 and Nb2O5-WO3 showed almost similar behavior with respect to characterization and catalytic activity. Surface area increased, X-ray diffraction (XRD) and Raman bands were lost, acid sites, both Brønsted and Lewis characters generated, and surface acid site density was as high as 2–4 nm−2. The acid sites were generated on the amorphous metal oxides consisting of Nb and Mo or W oxides, different in nature from those of Nb2O5 calcined and un-calcined, and active for Friedel-Crafts benzylation.