Photochemical synthesis of Pd nanocatalysts stabilized by biomass-derived polymers: from colloidal to supported systems in batch and flow

This study reports a novel light-driven methodology for the sustainable synthesis of Pd-based nanocatalysts. The approach features operational simplicity, short reaction times, and environmental friendliness. The visible light-induced reduction of Pd²⁺ precursors, allowed for the efficient production of both colloidal and silica-supported palladium nanoparticles (Pd-NPs), stabilized with either polyvinylpyrrolidone (PVP) or carboxymethylcellulose (CMC). The method was successfully implemented in batch and continuous-flow systems, demonstrating excellent scalability and control over the nanoparticle size (<5 nm) of Pd-NPs. The synthesized nanocatalysts exhibited excellent catalytic performance in Suzuki-Miyaura cross-coupling reactions under mild conditions, achieving turnover frequencies (TOFs) of 3733 h^-1 for Pd-CMC NPs and 3126 h^-1 for Pd-PVP NPs. For heterogeneous catalysts, <i>in situ</i> photoreduction was identified as the most effective immobilization strategy, producing highly active and uniformly dispersed Pd-NPs on silica nanoparticles (SNPs). These supported catalysts showed high recyclability, minimal Pd leaching, and consistent catalytic performance over multiple cycles. XPS and FT-IR characterization confirmed the presence of CMC and citrate as key stabilizing agents in the nanocatalysts, providing insight into the surface chemistry and stability of the materials. Furthermore, the successful implementation of a continuous-flow methodology for both colloidal and supported systems highlights the method's scalability and control over nanoparticle morphology. Overall, this work highlights the robustness and versatility of the photochemical strategy, offering a green and practical route to reusable Pd nanocatalysts for modern catalytic applications.