Effects of linker substitution on catalytic properties of porous zirconium terephthalate UiO-66 in acetalization of benzaldehyde with methanol

A family of isoreticular metal-organic frameworks (MOFs), based on the UiO-66 structure, were synthesized from the two linker ligands containing electron-donating NH₂-groups (2-amino-benzenedicarboxylic acid (H₂N-H₂BDC)) and electron-withdrawing NO ₂-groups (2-nitro-benzenedicarboxylic acid (O₂N-H ₂BDC)). The catalytic performance of these materials was investigated with a combination of physicochemical and catalytic approaches in acetalization of benzaldehyde with methanol. The investigation of basicity and Lewis acidity was done by IR spectroscopy using CDCl₃ and 5-nonanone as probe molecules, respectively. The combination of physicochemical and catalytic investigations demonstrates that acid-base and catalytic properties of these materials depend on amount and type of functional groups presented in the linker units. Insertion of electron-donating NH₂-groups into linker ligand leads to increase in the strength of basic sites in contrast to electron-withdrawing NO₂-groups. The strength of Lewis acid sites decreases in order of UiO-66-NO₂ > UiO-66 > UiO-66-NH ₂, that leads to the decrease in their catalytic activity in acetalization of benzaldehyde with methanol in the same order.