Metal–organic frameworks for catalysis: the Knoevenagel reaction using zeolite imidazolate framework ZIF-9 as an efficient heterogeneous catalyst

Crystalline zeolite imidazolate framework ZIF-9 was synthesized from the reaction of cobalt nitrate hexahydrate and benzimidazole by a solvothermal method, and was used as an efficient heterogeneous catalyst for the low temperature liquid phase Knoevenagel reaction. The solid catalyst was characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic laser light scattering (DLS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. Excellent conversions were achieved under mild conditions. The ZIF-9 catalyst was easily isolated from the reaction mixture by simple filtration and reused several times without a significant degradation in activity. Moreover, there was no contribution from leached active species and conversion was only being possible in the presence of the solid catalyst.