Generation of Bronsted acid sites on Al2O3-supported Ta2O5 calcined at high temperatures

An alumina-supported tantalum oxide (Ta2O5/Al2O3) calcined at 1223 K promoted both Friedel-Crafts alkylation of anisole with benzyl alcohol and isomerization of alpha-pinene, and exhibited Bronsted acidity despite the high temperature calcination. Among the Ta2O5/Al2O3 catalysts tested, 33 wt% Ta2O5/Al2O3 calcined at 1223 K showed the highest activity. A monolayer of tantalum acid-like compound, which has distorted octahedral symmetry, was stabilized over 33 wt% Ta2O5/Al2O3 catalyst calcined at 1223 K. The two-dimensional Ta-O-Ta network of stabilized tantalum acid-like compound probably accounts for the generation of Bronsted acid. (c) 2012 Elsevier B.V. All rights reserved.