Palladium-incorporated chitosan microspheres via inverse emulsion: a highly active and stable heterogeneous catalyst for Heck reactions

Abstract

Chitosan has emerged as a promising support for transition metal catalysts, owing to its abundant natural occurrence, robust chelating capacity, and inherent biodegradability. In this work, chitosan-supported palladium microspheres (Pd@MicroCS) were successfully fabricated via an inverse emulsification method. The synthesis involved the incorporation of Pd²⁺ cations into chitosan microspheres, followed by reduction to active Pd⁰ species using NaBH₄. The surface morphology of the resultant microspheres was characterized by scanning electron microscopy (SEM), while the dispersion of palladium nanoparticles was analyzed via transmission electron microscopy (TEM). The catalytic performance of this novel Pd@MicroCS catalyst was evaluated using the Heck coupling reaction. Under optimized reaction conditions, Pd@MicroCS exhibited exceptional catalytic activity in the coupling of substituted iodobenzene with alkenes. Notably, the spherical architecture of Pd@MicroCS facilitated straightforward separation and recycling. The catalyst maintained a coupling yield of over 90% even after 14 consecutive reuse cycles, with minimal palladium leaching (<2.0 wt%) in each cycle. Overall, this study presents a facile strategy for the preparation of a highly active and stable chitosan-supported palladium microsphere catalyst.