Gallium exchanged phosphotungstic acid supported on zirconia: Efficient catalyst for Friedel-Crafts benzylation

Gallium exchanged phosphotungstic acid (GaTPA) supported on zirconia catalysts were prepared and their physico-chemical properties were derived from FT-infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed desorption of ammonia, pyridine adsorbed FT-IR spectra and solid state super(31)P NMR spectroscopy. The catalysts activity was studied for Friedel-Crafts benzylation of anisole with benzyl alcohol. The characterization of catalysts revealed that the primary Keggin structure remained intact during exchange of TPA protons with Ga super(3+). The exchange of Ga super(3+) with the protons of TPA led to increase in Lewis acidity. Benzylation activity depended on the amount of the GaTPA and the catalyst with 20 wt% GaTPA supported on zirconia showed highest activity. The activity profiles of the catalysts were well correlated with the characteristics of the catalysts. Reaction parameters such as effect of reaction temperature, catalyst weight, anisole to benzyl alcohol molar ratio were also optimized. Under optimized conditions complete conversion of benzyl alcohol was obtained. The catalyst is reusable with consistent activity.