Heterogenizing homogeneous cocatalysts by well-designed hollow MOF-based nanoreactors for efficient and size-selective CO2 fixation

The fixation of CO2 with epoxides is a promising strategy to reduce CO2 emission. However, homogeneous halogen-based cocatalysts are often requisite for most heterogeneous catalysts to obtain desired activities, which significantly complicates the subsequent product purification/separation. Herein, we report the heterogenization of homogeneous Br-based cocatalysts by encapsulating them into stable and recyclable ZIF-8-based hollow nanoreactors (ZIF-8-HS) for efficient CO2 fixation. The synthesis involves in epitaxial growth of a size-controlled ZIF-8 layer on hollow ZIF-67 spheres prepared by using Br-contained surfactants as templates, followed by etching the unstable ZIF-67 shell. In ZIF-8-HS, the Br-contained surfactants can serve as efficient cocatalysts to activate substrates, while the microporous ZIF-8 shell possesses abundant intrinsic active sites and offers the cocatalysts a confined homogeneous environment. Impressively, ZIF-8-HS shows high activity, good size-selectivity and excellent recyclability for the CO2 fixation with epoxides, fully exploiting the respective advantages of homogeneous CTAB and heterogeneous ZIF-8 for this reaction.