Chemical recycling of polycarbonate and biodiesel synthesis catalyzed over Brønsted acid sites of ionic POMs: waste to valuable chemicals

Many chemical reactions require catalysts to achieve high product yields, including biodiesel synthesis and polymer depolymerization. Therefore, six new V-POMs and Mo-POMs (polyoxometalates) were synthesized, and their crystal structures were determined using single-crystal X-ray diffraction (SCXRD). These well-defined catalysts were employed in two transesterification (methanolysis) processes: biodiesel synthesis from rapeseed oil and chemical recycling of polycarbonate (PC). In addition to model reactions, waste cooking oil and waste CDs were used as feedstocks to demonstrate the practical applicability of the processes. Mo-POMs achieved complete PC conversion (100%) within 1 h at 130℃ using 1 wt% catalyst. Under optimized depolymerization conditions, BPA yields of approximately 90% were also obtained. The catalytic activity appears to reflect a combination of acidity, effective active-site accessibility, and structural stability of the POM framework. The kinetic stability of the catalysts was high, and only a slight decrease in PC conversion was observed during 4 catalyst recycling cycles. Moreover, in the biodiesel synthesis process, the same catalysts provided biodiesel yield up to 93% at 130°C during a 5-hour process. Hot-filtration and ICP-OES results indicate partial leaching of Mo - containing species, which remains the main limitation for recyclability; therefore, the system should be described as quasi -heterogeneous. Nevertheless, this work demonstrates that well-defined, ionic V-POMs and Mo-POMs are efficient catalysts for the transformation of waste into valuable chemical compounds.