Vapor-Phase Cyclohexene Epoxidation by Single-Ion Fe(III) Sites in Metal–Organic Frameworks

Abstract

Heterogeneous catalysts supported on metal–organic frameworks (MOFs), which possess uniform porosity and crystallinity, have attracted significant interest for recent years due to the ease of active-site characterization via X-ray diffraction and the subsequent relation of the active site structure to the catalytic activity. We report the syntheses, structures, and oxidation catalytic activities of single-ion iron catalysts incorporated into the zirconium MOF NU-1000. Single-ion iron catalysts with different counteranions were anchored onto the Zr node through postsynthetic solvothermal deposition. Crystallographic characterization of the resulting MOFs (NU-1000-Fe-Cl and NU-1000-Fe-NO3 ) revealed that, while both frameworks have similar Fe coordination, the distance between Fe and the Zr6 node differs significantly between the two. The product rate profiles of the two catalysts for vapor-phase cyclohexene epoxidation demonstrate different initial rates and product formations, likely originating from the different Fe–O distances.

Modulating Chemical Environments of Metal–Organic Framework-Supported Molybdenum(VI) Catalysts for Insights into the Structure–Activity Relationship in Cyclohexene Epoxidation

“…Negligible amounts of cyclohexenone were found in all reactions. As previously reported, − the homolytic activation of the oxidant (H 2 O 2 ) produces cyclohexenone and cyclohexenol as the radical oxidation products via a reaction of two cyclohexenyl hydroperoxide intermediates. Moreover, one cyclohexenyl hydroperoxide intermediate can react with a cyclohexene to produce epoxide and cyclohexenol, which can explain why the yield of alcohol is higher than that of ketone.…”

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

“…and Zr nodes have been previously seen in MOFs, 52 and DEAC dimers are reasonably stable at room temperature against dissociation to the monomeric species. [53][54][55] As has been shown with other alkyl aluminum species, 53 diethylaluminum chloride (DEAC) exists as a dimer in solution at room temperature.…”

Mesoporous Nitrogen-Doped Graphitized Carbon for Recyclable Oxidation of Cyclohexene

“…The formation of peroxyl radicals through the Harber–Weiss cycle is the initiation for the oxidation process of hydrocarbons in the liquid phase, which leads to the propagation of the radical chain reaction . In this regard, some metal salts with variable valence can promote the process through the redox effect, such as Co, Mn, Fe, and so forth. − Various metal organic frameworks or metal oxide contain mixed-valence metals could realize oxidation of cyclohexene through either the allylic or epoxidation pathway. − Peng and co-workers have made outstanding achievements in C–H bond oxidation, especially the application of carbon-based catalysts. They took the lead in developing metal-free catalysts in cyclohexene oxidation with the application of carbon nanotubes (CNTs) and nitrogen-doped CNTs using molecular oxygen as the oxidant. , The N-doped CNTs show significant improvement in activity for the nitrogen dopants and enhance the interaction between radicals and carbons.…”