Magnetically-separable Fe3O4@SiO2@SO4-ZrO2core-shell nanoparticle catalysts for propanoic acid esterification

© 2018 Elsevier B.V. Monodispersed, sulfated zirconia encapsulated magnetite nanoparticles were synthesized as magnetically-separable solid acid catalysts. Catalyst nanoparticles are prepared via coating preformed 80 nm Fe2O3particles with a 15 nm SiO2protective coating prior to growth of a uniform 28 nm ZrO2shell. The thickness of the ZrO2shell in resulting Fe3O4@SiO2@ZrO2nanoparticles was controlled by adjusting the zirconium butoxide to Lutensol AO5 ratio, with 1:10 found as the optimal ratio to produce monodispersed ZrO2coated nano-spheres. Sulfation using an ammonium sulfate precursor is less corrosive towards the core-shell structure of Fe3O4@SiO2@ZrO2nanoparticles leading to superior sulfated materials compared to those obtained using H2SO4. Resulting Fe3O4@SiO2@SO4-ZrO2solid acid catalysts exhibit high activity for propanoic acid esterification with methanol, far exceeding that of conventional sulfated zirconia nanoparticles, while being amenable to facile magnetic separation.