POM@IL-MOFs – inclusion of POMs in ionic liquid modified MOFs to produce recyclable oxidation catalysts

Abstract

In this study, we present for the first time the immobilization of phosphotungstic acid (H₃PW₁₂O₄₀, HPW) into the nanocages of a dual amino-functionalized ionic liquid (DAIL)-modified MIL-101(Cr) framework under mild conditions. The obtained PW/DAIL/MIL-101(Cr) was evaluated as a catalyst in the oxidation of benzyl alcohol using TBHP in chloroform. In order to obtain insights into the role of the DAIL during catalysis, a DAIL-free catalyst (HPW/MIL-101(Cr)) was also prepared. Both catalysts were fully characterized using several techniques. In comparison with the HPW/MIL-101(Cr) material, PW/DAIL/MIL-101(Cr) showed an enhanced catalytic performance in the selective oxidation of benzyl alcohol. This was mainly attributed to the ability of the DAIL groups to form hydrogen bonds, thus enhancing the accessibility of TBHP. Furthermore, the immobilization of the DAIL groups onto MIL-101(Cr) resulted in increased thermal stability of the obtained PW/DAIL/MIL-101(Cr) which showed stability up to 400 °C. Moreover, the PW/DAIL/MIL-101(Cr) catalyst exhibited good recyclability and selectivity. The catalyst could be reused for at least five cycles with no significant leaching of the tungsten species or loss of crystallinity and activity.