Efficient mesoporous SO₄²⁻/Zr-KIT-6 solid acid catalyst for green diesel production from esterification of oleic acid

Highly ordered mesoporous sulphated Zr-KIT-6(x) [x = Si/Zr] solid acid catalysts were successfully synthesized by hydrothermal method. Different weight fractions of zirconium were loaded into fixed gel in the acidic medium and then sulphated to get sulphated Zr-KIT-6(x) catalysts. X-ray diffraction (XRD), surface area analysis (Brunauer-Emmett-Teller equation) and microscopic techniques (SEM and TEM) results suggest the incorporation of Zr⁴⁺ into the silica KIT-6 framework by isomorphous substitution between Zr⁴⁺ and Si⁴⁺ ions. Diffuse reflection spectroscopy (DRS-UV) results reveal that Zr atoms are highly dispersed in +4 oxidation state. During the experiments it was observed that sulphated Zr-KIT-6 (20) showed the highest catalytic conversion for esterification of oleic acid (96%) and transesterification of jatropha oil (85%) at an optimized reaction conditions of 120 °C, 20:1 methanol to reactant molar ratio, 4 wt% catalyst loading and 6 h reaction time. The ester yields of 95% and 80% obtained from oleic acid and jatropha oil respectively. The used catalysts could be recycled up to three cycles with significant activity and stability.