Ultra-fine Pd nanoparticles confined in a porous organic polymer: A leaching-and-aggregation-resistant catalyst for the efficient reduction of nitroarenes by NaBH 4 .

Porous organic polymers (POPs) containing nitrogenous substituents have potential practical applications as heterogeneous catalysts based upon controlled porous structure and surface-anchored noble metal nanoparticles (NMNPs). In this work we prepared a POP material from piperazine and cyanuric chloride starting materials (PC-POP). The PC-POP material contains numerous triazinyl moieties, thus rendering the pores hydrophobic. Subsequently, by means of a novel reverse double-solvent approach (RDSA), microdroplets of Pd(AcO)2/CH2Cl2 were introduced into the hydrophobic pores of PC-POP in an aqueous environment; Pd(II) was rapidly reduced by NaBH4 to form ultra-fine Pd NPs and confined within the pores of PC-POP at high dispersity. The extensive porosity and dispersity of the Pd NPs made the active sites readily accessible, and led to efficient mass transfer. Thus, Pd@PC-POP exhibits superior catalytic performance in catalytic reduction of various nitroarenes. Furthermore, Pd@PC-POP has excellent recyclability, without significant loss of activity nor leaching of Pd active sites during 10 successive reaction cycles. This work points to a practical and cost-effective approach to preparation of POP materials, and also for confining ultra-fine NMNPs in POPs for use as catalysts.