Evaluation of basic sites of ZIFs metal organic frameworks in the Knoevenagel condensation reaction

Abstract

Metal-organic frameworks represent a new class of hybrid inorganic-organic materials which are characterized by high stability, high porosity and well-defined crystalline structures. One of their applications is in Catalysis, where bifunctional catalysts may be developed, with both acidic and basic sites. Zeolitic imidazole framework (ZIF) is a subfamily of MOFs which combines the advantages of MOFs with high thermal and chemical stability of zeolites. The objective of this work is to evaluate the basic character of synthetized ZIFs (ZIF-8 and ZIF-67). Samples were characterized by N2 adsorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). The Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate was chosen as model reaction to evaluate the basic sites. The reaction was conducted at 40°C and aniline was used as homogeneous catalyst for comparison. Characterization has shown high crystallinity, the presence of functional groups typical of ZIFs structures and high thermal stability. Both ZIF catalysts have shown good catalytic activity (around 90% at 8h of reaction), similar to the activity of aniline, a homogeneous catalyst. So the presence of basic sites of ZIF-8 and ZIF-67 and their activity were proven in this work.