Immobilization of palladium nanoparticles on polydopamine spheres with superior activity and reusability in Heck reaction

Polydopamine-based coating catalysts have garnered increasing attention in the field of heterogeneous catalysis. In this study, we developed a novel immobilized palladium (Pd) catalyst by incorporating polydopamine (PDA) spheres for efficient catalyze Carbon-Carbon coupling reaction. The Pd/PDA-X and Pd/PDA-IP catalysts were thoroughly characterized using Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), confirming the successful preparation of polydopamine spheres. Furthermore, high-resolution TEM analysis revealed that the palladium particles in these catalysts maintained highly dispersion. Notably, the apparent activation energy for the initial Heck reaction was significantly lower for the Pd/PDA-0 h catalyst (85.6 kJ/mol) compared to that of Pd/PDA-24 h (226.9 kJ/mol). Additionally, the initial Heck reaction rate of Pd/PDA-0 h catalyst was approximately 6.4 times higher than that of Pd/PDA-24 h catalyst. Moreover, extensive substrate scope (39 examples) studies employing Pd/PDA-0 h catalyst demonstrated high yields ranging from 61 % to 99 %, with remarkable stability observed even after nine cycles of reuse while maintaining a yield of 91 %. Conversely, sharp decreases in reaction yields were observed upon second reuse with Pd/PDA-24 h, highlighting the superior stability exhibited by our developed Pd/PDA-0 h catalyst and underscoring its potential for large-scale applications in Heck reactions.