Polyurethanes (PUNs) have been widely used in many fields. However, there are few reports on their microsphere preparation through precipitation polymerization. Herein, uniform PUN microspheres are prepared by precipitation polymerization of toluene diisocyanate and trimethylolpropane, without any surfactant and stabilizer. Under optimized conditions, monomers are fully polymerized within 2 h at a monomer concentration as high as 25.0 wt %, with a high yield of the microspheres (96.9%). By loading Pd on their surface, composite microspheres Pd@PUN are obtained and used as catalysts. 4-Nitrophenol is completely reduced within 1 min, with a kinetic constant of 4.96 min–1, significantly higher than many reported Pd-loaded catalysts, and with comparable reusability. Used in degradation of dye molecules, the catalytic performance is practically unchanged after 20 recycled uses. This work provides a simple method for the preparation of highly uniform PUN microspheres with a high yield and their Pd-loaded catalysts, both of great potential for various applications.

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Developing efficient supports for transition-metal nanoparticles (M-NPs) to prevent their agglomeration and to facilitate their handling and recycled use has been a constant objective. Herein, porous polyurea (PPU) is prepared by simple precipitation polymerization of toluene diisocyanate through its reaction with water in water–acetone, followed by Pd­(OAc)2 immobilization on a PPU surface to get Pd­(OAc)2@PPU and by Pd­(OAc)2 reduction to get a hybrid composite Pd@PPU with Pd-NPs on a PPU surface. Multiple characterizations revealed that the porous structure of PPU was retained in Pd­(OAc)2@PPU and Pd@PPU. Pd NPs were well dispersed on the Pd@PPU surface with a mean diameter of 7.18 nm. Pd@PPU was used as catalyst for reduction of toxic hexavalent chromium Cr­(VI) to benign trivalent chromium with formic acid as the reducer. A higher catalytic performance was detected compared to that of reported heterogeneous catalysts under similar conditions. A slight decrease in catalytic activity was detected in recycled use of the catalyst, which is ascribed to CO poisoning, a byproduct in formic acid decomposition. Full regeneration was obtained by heating the catalyst under N2 atmosphere for 2 h at 180 °C. This work provides therefore a novel approach for the preparation of a Pd@PPU catalyst of high performance for Cr­(VI) reduction, featured by low cost, facile synthesis, easy handling, and reusability.

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