Abstract
Extensive studies have been done on the modification of the organic linkers with different functional groups for ameliorating the properties of Zr-based metal-organic frameworks (MOFs). In contrast, little effort has been devoted to Zr MOF modification at the –OH group arising from the incomplete coordination of Zr with the organic linkers. We focused on covalently immobilizing redox-active iron to the –OH group in the node of a Zr-based MOF for selective oxidation of benzyl alcohol to benzaldehyde, which is an important reaction in organic synthesis, pharmaceutical, and industrial areas. In this work, iron acetylacetonate was incorporated into Zr6(μ3-O)4(μ3-OH)4(HCOO)6(1,3,5-benzenetricarboxylate)2 or MOF-808. The air-stable Fe-anchored MOF-808 (Fe-MOF-808) was subjected to screening for the selective oxidation of benzyl alcohol to benzaldehyde. Fe-MOF-808 showed enhanced conversion and selectivity to benzaldehyde as well as catalytically outperforming the pristine MOF-808 in the reaction. The prepared solid catalyst also displayed the robustness without the leaching of the active site during the reaction, along with at least four-time recyclability of use without significant deactivation.
Highlights
Selective oxidation of alcohol to aldehyde is of great importance in both academic research and industries
Metal-organic frameworks (MOFs)-808 possesses the –OH sites at the Zr node that can act as a molecular scaffold for covalent immobilization of desired active metals via atomic layer deposition in MOFs23,24 and solvothermal deposition in MOFs25,26 to generate the catalyst for various types of reactions
One formate coordinated to the Zr6(μ3-O)4(μ3-OH)4 node of MOF-808 was removed upon activation by heating under vacuum to create the –OH group (Fig. 1)
Summary
Selective oxidation of alcohol to aldehyde is of great importance in both academic research and industries. The commercial process for manufacturing benzaldehyde employs the chlorination of toluene to generate benzyl chloride, followed by hydrolysis and oxidation to yield benzaldehyde, which generates toxic halogenated wastes.. Noble metal clusters including Au, Pd, and Au–Pd bimetallic systems have been developed as catalysts for halogen-free production of benzaldehyde from biomass-derived benzyl alcohol.. The use of inexpensive redox-active metals such as Fe-based catalysts offers a good alternative they are still scarcely reported in comparison to the precious metal catalysts. Fe-based compounds are redox-active species and are capable of catalyzing numerous selective oxidations in a similar fashion to Fe-containing metalloenzymes in biological processes.. Fe complexes have been reported for their potential use as homogeneous catalysts for the oxidation of benzyl alcohol to benzaldehyde.. Fe-based compounds are redox-active species and are capable of catalyzing numerous selective oxidations in a similar fashion to Fe-containing metalloenzymes in biological processes. In particular, Fe complexes have been reported for their potential use as homogeneous catalysts for the oxidation of benzyl alcohol to benzaldehyde. The impregnation of Fe-based catalytic sites on a proper solid support to generate heterogeneous catalysts would yield promising catalytic activity and reusability
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