Zinc Zeolitic Imidazolate Frameworks as Base Catalysts: Tuning Catalytic Properties via Variation of Basicity and Crystal Size
Nowadays, a new subclass of metal-organic frameworks (MOFs), such as zeolitic imidazolate frameworks (ZIFs), have attracted considerable attention as materials for catalysis due to combination of structure of zeolites and physicochemical properties of MOFs in one material. Here we demonstrated investigation of catalytic potential of zinc zeolitic imidazolate frameworks based on 2-methyl- (ZIF-8), 2-ethylimidazolate (MAF-5 and MAF-6) and imidazolate-2-carboxyaldehyde (ZIF-90) linkers in three important catalytic reactions, such as (a) synthesis of 1-methoxy-2-propanol (PGME) from methanol and propylene oxide, (b) synthesis of erythrulose (the monosaccharide) via aldol condensation of formaldehyde and dihydroxyacetone and (c) synthesis of cyclic carbonates from CO2 and epoxides. Effect of structure and chemical composition on the reaction rate and distribution of products was investigated by a combination of catalytic and physicochemical methods, including X-ray powder diﬀraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption and Infrared spectroscopy using CDCl3 as probe molecule. It was found that efficiency of ZIFs materials depends on their basicity, structure of solids and crystal size which affects the different localization and accessibility of active sites, and the diffusion of reactants to the active sites.