Bilayer MOF@MOF and MoOx species functionalization to access prominent stability and selectivity in cascade-selective biphase catalysis

Article abstract of DOI:10.1016/j.mcat.2021.111818

A novel bilayer metal-organic framework (viz., MOF@MOF, based on Zr-MOFs via epitaxial growth of UiO-bpy on preformed UiO-66) assembled with two-dimensional MoO_x species was designed and synthesized. The MoO_x@UiO-66@MoO_x@UiO-bpy composite would improve substrates/products diffusion, avoid active metals leaching, and crucially provide a new platform via trapping intermediates and regulating the desired reaction direction. As confirmed via characterization results, MoO_x@UiO-66@MoO_x@UiO-bpy with micro-/mesopores and strong acid sites (Lewis and Br?nsted) exhibited good thermal and chemical stability. The bilayer MoO_x@UiO-66@MoO_x@UiO-bpy was further tested in cascade-selective biphase cyclopentene oxidation and exhibited 10.3% cyclopentene conversion and 16.9% glutaric acid selectivity higher than those of MoO_x@UiO-66, due to its large specific surface area, high content of MoO_x species, micro-/mesoporous structure, and bilayer catalytic effect. Its good reusability (> 10 runs) in the solvent-free-biphase cyclopentene oxidation suggested multidimensional encapsulation of active species in bilayer MOFs providing new idea for designing high-selectivity/stability heterogeneous catalysts. Besides, a set of reaction kinetic models with detailed kinetic parameters and a detailed reaction mechanism were provided, reconfirming the key to develop the technology of cyclopentene to glutaric acid was to conquer cyclopentene oxide hydrolysis activation energies (E₂ and E₄). Compared to our previous study, E₂ and E₄ values were decreased 93.8 and 31.7 kJ?mol^?1, respectively.