Engineering polyoxometalate anions on porous ionic network towards highly catalytic active noble metal clusters

Abstract

High surface energy of noble metal clusters (NMCs) with sub-nanometer size (<2 nm) endows their remarkable catalytic activity but naturally increases the risk of deactivation due to aggregation or oxidation. As a result, it is challengeable to construct efficient and stable naked NMCs. Herein, we reported the solvothermal synthesis of polyhedral oligomeric silsesquioxane (POSS) based porous ionic polymers with large surface areas, tunable pore structures and abundant ionic sites that resemble the structure of traditional ionic liquids. A series of highly dispersive and stable NMCs (Pd, Pt, Ru and Rh) were generated on these polymers by modulating their polyoxometalate (POM) anions, attributable to their robust framework and ion-exchange property. These organic cations paired POM anions are found to provide versatile strong interaction towards noble metal species, responsive for the formation and stabilization of NMCs. The obtained Pd clusters effectively catalyzed the solvent-free oxidation of benzyl alcohol with atmospheric dioxygen (O2), affording a high yield of 97% and a huge turnover number (TON) that exceeded 639 times of commercial Pd/C catalyst. The catalyst also exhibited pleasurable reusability and broad substrate compatibility.