An Exceptionally Stable Metal–Organic Framework Supported Molybdenum(VI) Oxide Catalyst for Cyclohexene Epoxidation

Abstract

Molybdenum(VI) oxide was deposited on the Zr node of the mesoporous metal-organic framework NU-1000 via condensed-phase deposition where the MOF is simply submerged in the precursor solution, a process named solvothermal deposition in MOFs (SIM). Exposure to oxygen leads to a monodisperse, porous heterogeneous catalyst, named Mo-SIM, and its structure on the node was elucidated both computationally and spectroscopically. The catalytic activity of Mo-SIM was tested for the epoxidation of cyclohexene. Near-quantitative yields of cyclohexene oxide and the ring-opened 1,2-cyclohexanediol were observed, indicating activity significantly higher than that of molybdenum(VI) oxide powder and comparable to that of a zirconia-supported analogue (Mo-ZrO) prepared in a similar fashion. Despite the well-known leaching problem of supported molybdenum catalysts (i.e., loss of Mo species thus causes deactivation), Mo-SIM demonstrated no loss in the metal loading before and after catalysis, and no molybdenum was detected in the reaction mixture. In contrast, Mo-ZrO led to significant leaching and close to 80 wt % loss of the active species. The stability of Mo-SIM was further confirmed computationally, with density functional theory calculations indicating that the dissociation of the molybdenum(VI) species from the node of NU-1000 is endergonic, corroborating the experimental data for the Mo-SIM material.

Size effect of the active sites in UiO-66-supported nickel catalysts synthesized via atomic layer deposition for ethylene hydrogenation

“…15 The decoration can be accomplished via A LD i n M OFs (AIM) 16–18 or s olvothermal deposition i n M OFs (SIM) 19–22 —as well as by AIM and SIM in combination. 23 Depending, of course, on their specific chemical composition, the resulting MOF-supported clusters or single metal ions can be rendered competent for photocatalytic H 2 generation, 24 electrocatalytic O 2 production, 25 solution-phase alkene epoxidation, 26, 27 and gas-phase ethylene hydrogenation and oligomerization, 13, 21, 28 hexene polymerization, 20 and propane oxidative dehydrogenation, 29 among other reactions. 22, 30 …”

Heterogeneous Epoxide Carbonylation by Cooperative Ion-Pair Catalysis in Co(CO)4–-Incorporated Cr-MIL-101

“…Other innate properties of Cr-MIL-101 that we deemed favorable for catalysis were its high hydrothermal and chemical stability, large surface area (4100 m 2 /g as measured by N 2 adsorption), large windows (12 and 16 Å) and pores (29 and 34 Å) for ready diffusion of reaction species, site-isolation of the Lewis acidic Cr(III) centers for robust catalysis, and facile synthesis using inexpensive chromium and terephthalic acid precursors. 21 Similar strategies to leverage the intrinsic stability, 22,23 porosity, 24,25 and site-isolation 26−28 of MOFs have proven to be effective in their applications to heterogeneous catalysis. Therefore, postsynthetic ion exchange of Co(CO) 4 – into Cr-MIL-101 was sought for the formation of a heterogeneous [Lewis acid] + [Co(CO) 4 ] − system.…”

Pore-size-tuned host–guest interactions in Co-MOFs via in situ microcalorimetry: adsorption and magnetism

“…20 (Table S6) However, the addition of guest molecules in the self-assembly process would probably disrupt the formation of the expected MOF framework due to the distortion of coordination geometry or template effect.…”