Hierarchical ZIFs@Al2O3 composite materials as effective heterogeneous catalysts

Abstract A facile growth of microporous ZIFs, such as ZIF-67, ZIF-8 into mesoporous alumina to obtain hierarchical micro/mesoporous ZIFs@Al2O3 is achieved. Several analysis techniques, such as powder-XRD, SEM, ICP, and gas adsorption, etc. are applied to characterize the composite materials. The use of a surfactant is the critical parameter to functionalize and assist the nano-crystal ZIFs growth in meso-Al2O3. To obtain a high crystal density ZIF-growth in meso-Al2O3 different parameters are tuned such as the surfactant (type and concentration), precursor concentration of ZIFs, and synthesis cycle of the composite material. The synthesis strategy is applicable for any ZIFs to be hybridized on supporting media such as meso-Al2O3. Furthermore, the application of ZIF-67@Al2O3 as a catalyst is examined and shows a high performance and recyclability for applications such as the Knoevenagel condensation and CO2 fixation reaction with epoxides. The highly active sites are distributed on a larger particle support (meso-Al2O3) is found to enhance the catalytic performance. Finally, the main advantage of the composite material is the straightforward handling compared to the use of bulk phases MOFs as a catalyst.