Heterogenizing homogeneous cocatalysts within ordered-mesoporous Core@microporous shell UiO-66 nanoreactors for efficient and size-selective CO2 cycloaddition with epoxides

A novel strategy is developed to heterogenize homogeneous cocatalysts. • Optimal nanoreactors are highly active and size-selective for CO 2 fixation. • The catalytic mechanism of CO 2 cycloaddition over OM@x-m-UiO-66/PBr is revealed. The cycloaddition of CO 2 with epoxides represents a promising strategy for mitigating CO 2 emissions. However, most heterogeneous catalytic systems still rely on homogeneous halogen-based cocatalysts to achieve desirable activities, which significantly complicates subsequent product purification and separation. Herein, we report a facile strategy to heterogenize homogeneous Br-based cocatalysts by encapsulating them into within stable UiO-66-based core–shell nanoreactors for efficient CO 2 fixation. Specifically, ordered mesoporous Ce-based UiO-66 (OM-UiO-66) was first synthesized via a soft-template method. The homogeneous Br-based cocatalyst was then adsorbed into the mesopores of OM-UiO-66, followed by epitaxial growth of a microporous Ce-based UiO-66 shell with controllable thickness to complete the encapsulation, thereby yielding a size-selective nanoreactor that possesses both 0.6 nm sieving channels and 10 nm reaction channels. Importantly, the synergistic interactions among the high concentration of the cocatalyst confined in the mesopores, the abundant Lewis acidic Ce sites on the pore walls, the mesoporous microenvironment that facilitates the enrichment of CO 2 and epoxide substrates, and the judiciously controlled thickness of the microporous shell collectively impart the as-prepared nanoreactor with high catalytic activity, excellent recyclability, and remarkable substrate size selectivity for the cycloaddition of CO 2 with epoxides under ambient conditions. This work not only develops a novel strategy for the efficient fixation of CO 2 via the heterogenization of homogeneous catalysts with a novel MOF-based core–shell architecture, but also provides a compelling paradigm for the heterogenization of other homogeneous catalysts. The heterogenization of homogeneous Br-based cocatalysts is realized by encapsulating them into a new kind of stable UiO-66-based core–shell nanoreactors for efficient and size-selective CO 2 cycloaddition with epoxides under ambient conditions. Download: Download high-res image (370KB) Download: Download full-size image