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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.

In this article, a set of fluorine functionalized covalent triazine-based frameworks have been designed and synthesized with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarbonitrile as the monomer under typical ionothermal conditions. A prominent defluorination process during synthesis etches the networks to release CFn, resulting in a significant loss of fluorine and carbon. Notably, the synergistic effects of polar C–F bonds and rich CO2-philic N sites bestow upon the framework an excellent H2 uptake (1.77 wt%, 77 K and 1 bar) as well as a significantly high CO2 adsorption capacity (5.98 mmol g−1, at 273 K and 1 bar), surpassing all related CTF materials measured under identical conditions that have been reported in the literature to date. Additionally, the material also exhibits a high CO2/N2 selectivity of 31 as predicted by the Henry model. The hydrophobicity of the CTF materials has been significantly enhanced owing to the incorporation of hydrophobic fluorine groups, which was further confirmed by ambient water vapor sorption.

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.

A new sulfone functionalized vanadium metal-organic framework (MOF), denoted as SO2-COMOC-2, has been synthesized solvothermally. Its structural and gas sorption properties towards CO2 and CH4 have been evaluated and compared to those of the pristine COMOC-2 material. The SO2-COMOC-2 shows a remarkable increase in CO2 capacity at ambient pressure (2.13 mmol g(-1) at 273 K vs. 1.23 mmol g(-1) for the pristine COMOC-2). Additionally, the high pressure CO2 sorption isotherm shows a distinctive two-step sorption behavior with a final capacity of 12.45 mmol g(-1) for SO2-COMOC-2 at 303 K, while for CH4 a typical Type I isotherm was obtained with a capacity of 4.13 mmol g(-1). In situ synchrotron X-ray powder diffraction measurements have been carried out to characterize the structural flexibility of the materials, showing both the presence of large pore and narrow pore form. Furthermore, synchrotron XANES and a variety of spectroscopic techniques have been utilized to verify the presence of hydroxyl groups and the existence of the mixed vanadium oxidation states in the titled MOF structure.

Doping the well-known metal-organic framework MIL-53(Al) with vanadium(IV) ions leads to significant changes in the breathing behaviour and might have repercussions on the catalytic behaviour as well. To understand the properties of such a doped framework, it is necessary to determine where dopant ions are actually incorporated. Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) are applied to reveal the nearest environment of the paramagnetic vanadium(IV) dopant ions. EPR spectra of as-synthesised vanadium-doped MIL-53 are recorded at S-, X-, Q- and W-band microwave frequencies. The EPR spectra suggest that at low dopant concentrations (1.0-2.6 mol%) the vanadium(IV) ions are well dispersed in the matrix. Varying the vanadium dopant concentration within this range or the dopant salt leads to the same dominant EPR component. In the ENDOR spectra, hyperfine (HF) interactions with H-1, Al-27 and V-51 nuclei are observed. The HF parameters extracted from simulations strongly suggest that the vanadium(IV) ions substitute Al in the framework.