A quaternary
ammonium and titanium codoped phosphotungstate (QA0.5Ti0.5H0.5PW) catalyst was prepared
by the ion exchange method and used as a solid acid catalyst for the
synthesis of n-butyl oleate. The catalyst was characterized
by Fourier transform infrared, elemental analyzer, energy-dispersive
X-ray spectrometry, Brunauer–Emmett–Teller, scanning
electron microscopy, and Hammett indicator methods. QA0.5Ti0.5H0.5PW showed a higher catalytic activity
than other phosphotungstate solid acid catalysts reported by literature,
and the esterification rate reached 99% under optimized conditions.
Moreover, QA0.5Ti0.5H0.5PW exhibited
well reusability. An esterification rate of 90.1% was still obtained
in the eighth run.