Post-synthetic anchoring Fe(III) into a fcu-type Zr-MOF for the catalyzed hydrolysis of 5-hydroxylmethoxyfurfural

Metal-organic frameworks (MOFs) featuring a fcu-type net based on 12-connected [Zr₆(μ₃-O)₄(μ₃-OH)₄] cluster have received considerable interest for the fundamental investigation of structure-property relationships in a wide range of catalytic reactions. In this work, the bipyridine (bpy) chelate group was introduced into the fcu-type framework of UiO-67, giving UiO-67bpy as the catalyst support. Then, FeCl₃ was post-synthetically anchored to the bpy group, resulting into the isolation of FeCl₃/UiO-67bpy. Catalyzed hydrolysis of 5-hydroxylmethoxyfurfural (HMF) into levulinic acid (LA) was then explored and revealed that it can efficiently and selectively catalytic convert HMF into LA, which is superior to that of FeCl₃/UiO-67 where FeCl₃ is encapsulated in the cage of UiO-67 and dispersed on the pore surface. The recyclability studies further confirmed the importance of anchored FeCl₃ where there is no significant decrease in catalytic activity as compared with that of FeCl₃/UiO-67. Taking the detailed textural porosity and catalytic results of isomorphous structures in consideration, our studies revealed that narrowing the pore size with anchored FeCl₃ on the skeleton of the fcu-type Zr-MOF rather than encapsulating FeCl₃ inside the cage is more favored for the rehydration reaction of HMF to LA.