Nanoarchitectured Eggshell-Like Co/W Bimetallic MOF as a Selective Catalyst for Cyclohexene Oxidation

Abstract

A nanoarchitectured eggshell-like Co/W bimetallic metal-organic framework (Co_xW_y-ZIF) nanoreactor was synthesized via a dissolution-regrowth process using ZIF-67 as a sacrificial template. The morphological evolution from rhombic dodecahedra to flower-like aggregates and finally to hollow eggshell-like nanocages was systematically controlled by tuning the Co/W ratio. Among the prepared catalysts, Co_71.56W_28.44-ZIF featured a well-defined eggshell-like architecture with a large pore size of 9.50 nm. XPS analysis revealed that its bimetallic shell is composed of Co(OH)₂ and CoWO₄ phases, which originate from the coordinated etching and regrowth process. This unique hollow structure not only facilitates mass transfer and enhances substrate accessibility but also provides abundant and stable redox-active sites due to the synergistic coexistence of Co and W species. In the catalytic oxidation of cyclohexene (CHE) using acetonitrile as solvent and H₂O₂ as oxidant, Co_71.56W_28.44-ZIF achieved 76.5% CHE conversion and an outstanding 79.5% selectivity to 2-cyclohexen-1-one (2-one), outperforming catalysts with higher surface areas but less favorable pore architectures. Moreover, the catalyst demonstrated good recyclability and structural stability over four consecutive runs, as confirmed by XRD, FT-IR, and SEM. These results highlight that the synergy between morphological control and compositional engineering is key to overcoming the trade-off between activity and selectivity in alkene oxidation.

Graphical Abstract