Differential guest location by host dynamics enhances propylene/propane separation in a metal-organic framework

Energy-efficient approaches to propylene/propane separation such as molecular sieving are of considerable importance for the petrochemical industry. The metal organic framework NbOFFIVE-1-Ni adsorbs propylene but not propane at room temperature and atmospheric pressure, whereas the isostructural SIFSIX-3-Ni does not exclude propane under the same conditions. The static dimensions of the pore openings of both materials are too small to admit either guest, signalling the importance of host dynamics for guest entrance to and transport through the channels. We use ab initio calculations together with crystallographic and adsorption data to show that the dynamics of the two framework-forming units, polyatomic anions and pyrazines, govern both diffusion and separation. The guest diffusion occurs by opening of the flexible window formed by four pyrazines. In NbOFFIVE-1-Ni, (NbOF5)2- anion reorientation locates propane away from the window, which enhances propylene/propane separation

Facile modifications of HKUST-1 by V, Nb and Mn for low-temperature selective catalytic reduction of nitrogen oxides by NH 3

International audienceHKUST-1 catalysts were impregnated with vanadium, niobium and manganese species and tested in NH 3-SCR for NO removal. No reduction of NO by NH 3 was registered for the unmodified HKUST-1 and disappearance of NO was attributed to adsorption. After a pretreatment at 185°C, the best catalytic performance was found for HKUST-1-Mn with 100% and 80% conversion of NH 3 and NO, respectively at 185°C. For the first time, the H 2 O tolerance was examined on the modified HKUST-1 catalyst. The addition of water vapor resulted in decrease of NO and NH 3 conversions, which was immediately recovered when H 2 O feeding was stopped. The NO conversion dropped from 76% to 68% after 35 min of H 2 O addition

Hydrothermal synthesis, ab-initio structure determination and NMR study of the first mixed Cu-Al fluorinated MOF

Herein, the first fluorinated heterometallic metal-organic framework (MOF) containing both Cu(II) and Al(III) cations is presented. CuAlF4.5(OH)(0.5)(H2O)[HAmTAZ](2) (HAmTAZ = 3-amino-1,2,4-triazole) was hydrothermally synthesized. The structure of this paramagnetic compound was solved using the SDPD method (structural determination by powder diffractometry) and confirmed by H-1, F-19 and Al-27 solid-state nuclear magnetic resonance (NMR) experiments. The structure (space group Ima2, a = 16.306(3) angstrom, b = 8.9356(3) angstrom, c = 8.2884(2) angstrom) can be described from the Cu-HAmTAZ layers connected by AlF5H2O octahedra, generating a three-dimensional network with a pcu topology. This compound illustrates that from 2D MOFs within the M(HTAZ)(2)(NCS)(2) (M = Mn, Fe, Co, Ni, Cu, Zn) system, insertion of AlF5H2O octahedra building units between the Cu-HAmTAZ layers provides a way to generate 3D F-MOFs

Perspectives in Adsorptive and Catalytic Mitigations of NOx Using Metal–Organic Frameworks

International audienceBecause of its high polluting effect, a growing research interest in NOx monitoring, removal, and control has been noticed in the last years. Motivated by the high degree of functional and structural tunability of metal–organic frameworks (MOFs), researchers explored potential MOF-based adsorbents, sensors, and catalysts for NOx mitigation/control. However, this area of research is still in its infancy. In addition, the physical–chemical properties of NOx make this task extremely challenging as some materials suffer relatively weak thermal and/or chemical stability. Nevertheless, some recent encouraging studies have demonstrated superior stability properties that enable MOFs to be considered as alternative benchmark materials for the capture and conversion of NOx. This review offers an overview on the recent progress made in this field and provides some interesting routes on the uses of MOFs for selective NOx adsorption, release, and/or catalytic conversion (via selective catalytic reduction or photocatalysis)

Achieving Superprotonic Conduction with a 2D Fluorinated Metal–Organic Framework

International audienceA hydrolytically stable metal–organic framework (MOF) material, named KAUST-7′, was derived from a structural phase change of KAUST-7 upon exposure to conditions akin to protonic conduction (363 K/95% relative humidity). KAUST 7′ exhibited a superprotonic conductivity as evidenced by the impedance spectroscopic measurement revealing an exceptional conductivity up to 2.0 × 10–2 S cm–1 at 363 K and under 95% RH, a performance maintained over 7 days. Ab initio molecular dynamics simulations suggested that the water-mediated proton transport mechanism is governed by water assisted reorganization of the H-bond network involving the fluorine moieties in KAUST-7′ and the guest water molecules. The notable level of performances combined with a very good hydrolytic stability positions KAUST-7′ as a prospective proton-exchange membrane alternative to the commercial benchmark Nafion. Furthermore, the remarkable RH sensitivity of KAUST-7′ conductivity, substantially higher than previously reported MOFs, offers great opportunities for deployment as a humidity sensor

Evolution of guanazolium fluoroaluminates within the composition-space diagram and with the temperature

The 2D composition-space diagram of the Al(OH)3−Am2TAZ−HFaq−ethanol system is established under microwave heating at 190 °C for [Al3+] = 1 mol·L−1. Four new fluoroaluminates are evidenced when the [HF]/[Am2TAZ] ratio is increased in the starting solution, and the dimensionality of the inorganic frameworks is increased from 0D in [HAm2TAZ]2·(AlF5(H2O))·2H2O (Pc, Z = 2), to 1D in [HAm2TAZ]2·(AlF5) and [HAm2TAZ]2·(Al2F8) (Fdd2, Z = 8), and to 2D in [HAm2TAZ]2·(Al5F17) (Imm2, Z = 2). This evolution is partially paralleled by the thermal decomposition of [HAm2TAZ]2·(AlF5(H2O))·2H2O; on heating, this hydrate gives [HAm2TAZ]2·(AlF5) at 100−150 °C and [HAm2TAZ]2·(Al2F8) at 180 °C; the loss and simultaneous decomposition of [HAm2TAZ]F leave a solid residue of polymeric paracyanogen (CN)2n that is further decomposed and hydrolyzed into HCN and HNCO by atmospheric water traces. NMR 19F spectroscopy of [HAm2TAZ]2·(AlF5) is in agreement with the crystallographic determination, and the 27Al spectrum demonstrates that a significant F−/OH− substitution is excluded

Turning a Methanation Catalyst into a Methanol Producer: In-Co Catalysts for the Direct Hydrogenation of CO2 to Methanol

The direct hydrogenation of CO2 to methanol using green hydrogen is regarded as a potential technology to reduce greenhouse gas emissions and the dependence on fossil fuels. For this technology to become feasible, highly selective and productive catalysts that can operate under a wide range of reaction conditions near thermodynamic conversion are required. Here, we demonstrate that indium in close contact with cobalt catalyses the formation of methanol from CO2 with high selectivity (>80%) and productivity (0.86 gCH3OH.gcatalyst-1.h-1) at conversion levels close to thermodynamic equilibrium, even at temperatures as high as 300 °C and at moderate pressures (50 bar). The studied In@Co system, obtained via co- precipitation, undergoes in situ transformation under the reaction conditions to form the active phase. Extensive characterization demonstrates that the active catalyst is composed of a mixed metal carbide (Co3InC0.75), indium oxide (In2O3) and metallic Co. </div