Catalytic Performance of a Novel Delignified Wood Rod-Based Micropacked-Bed Reactor

A highly efficient continuous-flow catalytic reactor was developed by immobilizing uniformly dispersed palladium nanoparticles (Pd NPs) on delignified wood rods, facilitating the effective and sustainable treatment of 4-nitrophenol (4-NP) wastewater. Natural wood was selected as the renewable substrate, which was first subjected to lignin extraction to create an open, vertically aligned pore structure. Subsequently, polydopamine (PDA) modification facilitated the layer-by-layer (LbL) self-assembly of poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), forming a positively charged polyelectrolyte film that served as a robust scaffold for Pd NP immobilization. Through ion exchange and in situ reduction, a uniformly distributed catalytic layer of Pd NPs was anchored onto the wood matrix. The optimized reactor featured interconnected, vertically oriented pores with reduced diameter, which not only maximized catalyst loading per unit volume but also enhanced the mass transfer of reactants to the active sites. Experimental results revealed that the reactor exhibited exceptional catalytic activity toward 4-NP, even at a high concentration of 4.5 mM, with an ultralow Pd loading of merely 0.11 wt %. Under the optimal reaction conditions of a sodium borohydride (NaBH 4 ) concentration of 125 mM, a 4-NP concentration of 4.5 mM, a polymer electrolyte layer comprising three layers, and a catalytic bed height of 3 cm, the reactor maintained continuous and stable operation for 200 h, maintaining a 4-NP conversion rate of over 98% throughout the entire period. This sustainable continuous-flow catalytic system, based on natural renewable materials, offers a cost-effective and environmentally friendly solution for the treatment of 4-NP-containing industrial wastewater and aligns with the principles of green catalysis and sustainable development.