Synthesis and Characterization of Sulfated TiO2 Nanorods and ZrO2/TiO2 Nanocomposites for the Esterification of Biobased Organic Acid

TiO2 nanorods and ZrO2-modified TiO2 nanocomposites have been prepared by hydrothermal synthesis and the deposition-precipitation method. Their sulfated products were tested as solid superacid catalysts for the esterification of levulinic acid which was used as a model bio-oil molecule. SEM and TEM characterization showed that TiO2 nanorods with diameters ranging from 20 to 200 nm and with lengths of up to 5 μm were synthesized by a hydrothermal method at 180 °C. ZrO2 nanoparticles with the diameters ranging from 10 to 20 nm were evenly deposited on TiO2 nanorods. IR and XPS results suggested that sulfated ZrO2/TiO2 nanocomposite has higher content of sulfate groups on the surface with a S/(Zr+Ti) ratio of 13.6% than sulfated TiO2 nanorods with a S/Ti ratio of 4.9%. The HPLC results showed that sulfated ZrO2/TiO2 nanocomposite have enhanced catalytic activity for esterification reaction between levulinic acid and ethanol compared to sulfated TiO2 nanorods. The conversion of levulinic acid to ethyl levulinate can reach to 90.4% at the reaction temperature of 105 °C after 180 min.