Monodispersed Hollow SO₃H-Functionalized Carbon/Silica as Efficient Solid Acid Catalyst for Esterification of Oleic Acid

SO₃H-functionalized monodispersed hollow carbon/silica spheres (HS/C-SO₃H) with primary mesopores were prepared with polystyrene as a template and p-toluenesulfonic acid (TsOH) as a carbon precursor and -SO₃H source simultaneously. The physical and chemical properties of HS/C-SO₃H were characterized by N₂ adsorption, TEM, SEM, XPS, XRD, Raman spectrum, NH₃-TPD, element analysis and acid-base titration techniques. As a solid acid catalyst, HS/C-SO₃H shows excellent performance in the esterification of oleic acid with methanol, which is a crucial reaction in biodiesel production. The well-defined hollow architecture and enhanced active sites accessibility of HS/C-SO₃H guarantee the highest catalytic performance compared with the catalysts prepared by activation of TsOH deposited on the ordered mesoporous silicas SBA-15 and MCM-41. At the optimized conditions, high conversion (96.9%) was achieved and no distinct activity drop was observed after 5 recycles. This synthesis strategy will provide a highly effective solid acid catalyst for green chemical processes.