Preparation and properties of zirconia nanotube-supported 12-tungstophosphoric acid catalyst

Zirconia nanotube-supported H₃PW₁₂O₄₀ (HPW) catalysts were obtained by loading HPW onto zirconia nanotube arrays which were prepared through anodization of zirconium foil in the mixture of formamide and glycerol (volume ratio = 1:1) containing 1 wt% NH₄F and 1 wt% H₂O. The samples were characterized through scanning electron microscope, X-ray diffraction, infrared spectra and thermogravimetric analysis. Various factors affecting the catalytic activities have been investigated. The catalysts, prepared through pretreating the nanotube carrier at 400 °C, followed by loading with 35 wt% HPW and calcining at 200 °C, possess high catalytic activities in the synthesis of fatty acid ethyl ester. Under the optimal reaction conditions, the conversion percentages of lauric acid, oleic acid and stearic acid are all higher than 98.5%.