Catalytic activity of La-modified phosphotungstic heteropoly acid salt in synthesis of biodiesel from esterification of methanol and oleci acid

La-modified phosphotungstic heteropoly acid salt catalyst was prepared by using H ₃PW ₁₂O ₄₀ and La(NO ₃) ₃as raw materials through the ion exchange method. The physical and chemical properties of the obtained-catalyst were analyzed with the employment of scanning electron microscopy, infrared spectroscopy and X-ray powder diffraction. The catalytic activity of the obtained-catalyst was studied in the esterification reaction with the oleic acid and methanol as raw materials. The results show that the rare earth lanthanum has been introduced into the skeleton structure of phosphotungstic heteropoly acid and formed new coordination bond with the heteroatom P, which effectively improved the specific surface area and pore size of phosphorus tungsten heteropoly acid; La-modified phosphotungstic heteropoly acid salt keeps the Keggin structure of phosphotungstic heteropoly acid completely. A yield of oleic acid methyl ester 88.0 % is obtained when the reaction temperature is 62 °C, the molar ratio of methanol and oleic acid is 1:6, reaction time is 4.5 h, and the mass ratio of catalyst to the reactants (oleic acid and methanol) is 2.5 %.