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The structural environment of the V-IV ions doped in the metal-organic framework (MOF) DUT-5(Al) (((AlOH)-O-III) BPDC) was studied with electron paramagnetic resonance (EPR). At low V concentrations, two different vanadyl components are observed in the EPR spectrum: a broad-line component, best visible at ambient air conditions, and a narrow-line component, becoming more prominent at lower pressures. Recording the EPR spectra at both X- and Q-band, spin-Hamiltonian parameters were derived for both components. Similarities between the spectrum of the narrow-line component and the spectrum of V-IV centers in the large pore state of a related MOF, MIL-53(Al) (((AlOH)-O-III)BDC), are discussed, including their sensitivity to oxygen. The broad-line component cannot conclusively be identified by comparison with V-IV centers in MIL-53(Al). Increasing the concentration of V-IV in the DUT-5(Al) framework, a third vanadyl component appears in the spectrum, together with a broad feature related to the spectrum of COMOC-2(V) ((V-IV =O)BPDC). Surprisingly, this third component appears to be linked with a narrow pore state of the mixed-metal MOF.

In this work, we report the catalytic performance of a MoO2Cl2 anchored metal-organic framework, Mo@COMOC-4, in the oxidative desulfurization (ODS) process on a continuous fixed-bed reactor. Mo@COMOC-4 was examined as a catalyst in the oxidation of model oils containing dibenzothiophene (DBT), benzothiophene (BT) or 4,6-dimethyldibenzothiophene (4,6-DMDBT). In a 50-h ODS reaction of DBT at 70 °C, with tert-butyl hydroperoxide (TBHP) as the oxidant, a constant high DBT conversion of nearly 80% was observed along with a high oxidant utility of over 85%, where DBT was converted rapidly into DBT sulfone. XRD and ICP analysis show that the structure of Mo@COMOC-4 was well preserved, with no significant leaching of Mo species. In addition, Mo@COMOC-4 can also oxidize a hydrogenated diesel oil, and 74% sulfur removal efficiency was achieved, with an extraction recovery of 92.5% after acetonitrile extraction. Spectroscopic characterization confirmed the formation of a molybdenum peroxide complex from MoO2Cl2 under TBHP treatment, a plausible catalytic process was proposed based on the experiment evidence as well as FT-IR and FT-FIR characterization results.

Two types of Mo containing metal-organic frameworks, denoted as Mo@COMOC-4 and PMA@MIL-101(Cr), were synthesized respectively by a post-synthetic modification and a ship-in-bottle approach. The catalytic performance of both compounds in the epoxidation of propylene using cumene hydroperoxide (CHP) as oxidant was compared with MoO3@SiO2. A higher conversion (46.2%) and efficiency (87.4%) of CHP was observed for Mo@COMOC-4, whereas the heteropoly acids supported MIL-101 resulted in the decomposition of CHP due to its strong acidic character. Regenerability tests demonstrated that Mo@COMOC-4 could be reused for multiple runs without significant loss in both activity and stability.

Using a one pot microwave procedure, mixed-metal “egg yolk” MOFs are created, with a core of (Cr/V)-MIL-53 and a shell of Cr-MIL-53. In contrast, the solvothermal method produces homogeneous mixed-metal MOFs. The influence of Cr and V on the flexibility and breathing was studied via T-XRPD and CO2 adsorption measurements.

A new series of bimetallic COMOC-2(V)/DUT-5(Al) frameworks are developed and fully characterized. Electron paramagnetic resonance and transmission electron microscopy confirm the homogeneous dispersion of Al/V in the entire framework. The study of the flexibility by means of CO2 pressure dependent XRPD and high pressure sorption reveals the co-existence of two different large pore phases and a narrow pore phase in the entire pressure regime.

In this work, the hydrothermal and chemical stability towards acids, bases, air, water, and peroxides of Metal Organic Frameworks, that are commonly considered to be stable, is presented. As a proof of stability both the crystallinity and porosity are measured before and after exposure to the stress test. The major part of the MOFs examined in this study show a good hydrothermal stability except for UiO-67, NH 2 -MIL-101 (Al) and CuBTC. The chemical stabilities towards acids and bases show a similar tendency and an ordering can be proposed as: MIL-101(Cr) > NH 2 -UiO-66 > UiO-66 > UiO-67 > NH 2 -MIL-53 > MIL-53(Al)>ZIF-8 > CuBTC > NH 2 -MIL-101(Al). In the tests with H 2 O 2 most materials behaved poorly, only the UiO-66 and NH 2 -UiO-66 frameworks show a good stability.

In this work, we present the successful synthesis of a series of sulfonic acid functionalized mixed-linker metal–organic frameworks (MOFs) having the DUT-4 topology by using different ratios of 2,6-naphthalenedicarboxylic acid (H2-NDC) and 4,8-disulfonaphthalene-2,6-dicarboxylic acid (H2-NDC-2SO3H) in one-pot reactions. The obtained materials were fully characterized and their CO2 adsorption properties at low and high pressures were studied and compared with those of the pristine DUT-4 material. Generally, the CO2 adsorption capacities range from 3.28 and 1.36 mmol g−1 for DUT-4 to 1.54 and 0.78 mmol g−1 for DUT-4-SO3H (50) up to 1 bar at 273 K and 303 K, respectively. Computational calculations corroborated the structural changes of the material in function of the loading of sulfonic acid groups. Furthermore, due to the strong Bronsted acid character, the resulting sulfonic acid based MOF material was evaluated as a catalyst for the ring opening of styrene oxide with methanol as a nucleophile under mild conditions, showing almost full conversion (99%) after 5 hours of reaction. A hot filtration experiment demonstrated that the catalysis occurred heterogeneously and the catalyst could be recovered and reused for multiple runs without significant loss in activity and crystallinity.

X-ray diffraction (XRD) and electron paramagnetic resonance spectroscopy (EPR) were combined to study the structural transformations induced by temperature, pressure and air humidity of the "breathing" metal-organic framework (MOF) MIL-53(Al), doped with paramagnetic V

X-ray diffraction (XRD) and electron paramagnetic resonance spectroscopy (EPR) were combined to study the structural transformations induced by temperature, pressure and air humidity of the breathing metalorganic framework (MOF) MIL-53(Al), doped with paramagnetic VIV ions, after activation. The correlation between in situ XRD and thermogravimetric analysis measurements showed that upon heating this MOF in air, starting from ambient temperature and pressure, the narrow pore framework first dehydrates and after that makes the transition to a large pore state (lp). The EPR spectra of VIV[double bond, length as m-dash]O molecular ions, replacing AlOH in the structure, also allow to distinguish the as synthesized, hydrated (np-h) and dehydrated narrow pore (np-d), and lp states of MIL-53(Al). A careful analysis of EPR spectra recorded at microwave frequencies between 9.5 and 275 GHz demonstrates that all VIV[double bond, length as m-dash]O in the np-d and lp states are equivalent, whereas in the np-h state (at least two) slightly different VIV[double bond, length as m-dash]O sites exist. Moreover, the lp MIL-53(Al) framework is accessible to oxygen, leading to a notable broadening of the VIV[double bond, length as m-dash]O EPR spectrum at pressures of a few mbar, while such effect is absent for the np-h and np-d states for pressures up to 1 bar.