Response Surface Optimization of Biodiesel Production via Esterification Reaction of Methanol and Oleic Acid Catalyzed by a Brönsted-Lewis Catalyst PW/UiO/CNTs-OH <i></i>

In this study, a Br&ouml;nsted-Lewis bifunctional acidic catalyst PW/UiO/CNTs-OH was synthesized via hydrothermal method. The esterification reaction parameters between oleic acid and methanol catalyzed by PW/UiO/CNTs-OH were optimized using central composite design-response surface methodology (CCD-RSM). The process achieved 92.9% biodiesel yield under optimized reaction conditions, retaining 82.3% biodiesel yield after four catalytic cycles. The enhanced catalytic performance of PW/UiO/CNTs-OH can be attributed as follows: the [Zr6O4(OH)4]12+ anchored on the surface of MWCNTs provides nucleation sites of UiO-66, enabling dual functions of HPW stabilization and Lewis acid site generation via quadrupole inversion. In addition, HPW introduction during synthesis of UiO-66 reduces solution pH, inducing the protonation of the p-Phthalic acid (PTA) to disrupt the coordination with the [Zr6O4(OH)4] cluster, thereby creating an unsaturated Zr4+ site with electron pair-accepting capability as additional Lewis acid sites. EIS analysis revealed that PW/UiO/CNTs-OH exhibited superior electron migration efficiency compared to UiO-66 and PW/UiO. Furthermore, NH3-TPD and Py-IR analysis showed that PW/UiO/CNTs-OH possessed high densities of Lewis acidic sites of 83.69 &mu;mol/g and Br&ouml;nsted acidic sites of 9.98 &mu;mol/g.