Synthesis, Crystal Structure and Catalytic Behavior of Homo- and Heteronuclear Coordination Polymers [M(tdc)(bpy)] (M²⁺ = Fe²⁺, Co²⁺, Zn²⁺, Cd²⁺; tdc^2– = 2,5-thiophenedicarboxylate)

A series of isostructural 3D coordination polymers ³_∞[M­(tdc)­(bpy)] (M²⁺ = Zn²⁺, Cd²⁺, Co²⁺, Fe²⁺; tdc^2– = 2,5-thiophenedicarboxylate; bpy = 4,4′-bipyridine) was synthesized and characterized by X-ray diffraction, thermal analysis, and gas adsorption measurements. The materials show high thermal stability up to approximately 400 °C and a solvent induced phase transition. Single crystal X-ray structure determination was successfully performed for all compounds after the phase transition. In the zinc-based coordination polymer, various amounts of a second type of metal ions such as Co²⁺ or Fe²⁺ could be incorporated. Furthermore, the catalytic behavior of the homo- and heteronuclear 3D coordination polymers in an oxidation model reaction was investigated

Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol–Gel Process Accompanied by Polymerization-Induced Phase Separation

Enhancing the activity and stability of catalysts is a major challenge in scientific research nowadays. Previous studies showed that the generation of an additional pore system can influence the catalytic performance of porous catalysts regarding activity, selectivity, and stability. This study focuses on the epoxide-mediated sol–gel synthesis of mixed metal oxides, NiAl₂O₄ and CoAl₂O₄, with a spinel phase structure, a hierarchical pore structure, and Ni and Co contents of 3 to 33 mol % with respect to the total metal content. The sol–gel process is accompanied by a polymerization-induced phase separation to introduce an additional pore system. The obtained mixed metal oxides were characterized with regard to pore morphology, surface area, and formation of the spinel phase. The Brunauer–Emmett–Teller surface area ranges from 74 to 138 m²·g^–1 and 25 to 94 m²·g^–1 for Ni and Co, respectively. Diameters of the phase separation-based macropores were between 500 and 2000 nm, and the mesopore diameters were 10 nm for the Ni-based system and between 20 and 25 nm for the cobalt spinels. Furthermore, Ni–Al spinels with 4, 5, and 6 mol % Ni were investigated in the dry reforming of CH₄ (DRM) with CO₂ to produce H₂ and CO. CH₄ conversions near the thermodynamic equilibrium were observed depending on the Ni content and reaction temperature. The Ni catalysts were further compared to a noble metal-containing catalyst based on a spinel system showing comparable CH₄ conversion and carbon selectivity in the DRM

Synthesis, Crystal Structure and Catalytic Behavior of Homo- and Heteronuclear Coordination Polymers [M(tdc)(bpy)] (M²⁺ = Fe²⁺, Co²⁺, Zn²⁺, Cd²⁺; tdc^2– = 2,5-thiophenedicarboxylate)

A series of isostructural 3D coordination polymers ³_∞[M­(tdc)­(bpy)] (M²⁺ = Zn²⁺, Cd²⁺, Co²⁺, Fe²⁺; tdc^2– = 2,5-thiophenedicarboxylate; bpy = 4,4′-bipyridine) was synthesized and characterized by X-ray diffraction, thermal analysis, and gas adsorption measurements. The materials show high thermal stability up to approximately 400 °C and a solvent induced phase transition. Single crystal X-ray structure determination was successfully performed for all compounds after the phase transition. In the zinc-based coordination polymer, various amounts of a second type of metal ions such as Co²⁺ or Fe²⁺ could be incorporated. Furthermore, the catalytic behavior of the homo- and heteronuclear 3D coordination polymers in an oxidation model reaction was investigated

Network Flexibility: Control of Gate Opening in an Isostructural Series of Ag-MOFs by Linker Substitution

An isostructural series of 15 structurally flexible microporous silver metal–organic frameworks (MOFs) is presented. The compounds with a dinuclear silver core as secondary building unit (Ag₂N₄) can be obtained under solvothermal conditions from substituted triazolyl benzoate linkers and AgNO₃ or Ag₂SO₄; they exhibit 2-fold network interpenetration with <b>lvt</b> topology. Besides the crystal structures, the calculated pore size distributions of the microporous MOFs are reported. Simultaneous thermal analyses confirm the stability of the compounds up to 250 °C. Interconnected pores result in a three-dimensional pore structure. Although the porosity of the novel coordination polymers is in the range of only 20–36%, this series can be regarded as a model system for investigation of network flexibility, since the pore diameters and volumes can be gradually adjusted by the substituents of the 3-(1,2,4-triazol-4-yl)-5-benzamidobenzoates. The pore volumes of selected materials are experimentally determined by nitrogen adsorption at 77 K and carbon dioxide adsorption at room temperature. On the basis of the flexible behavior of the linkers a reversible framework transformation of the 2-fold interpenetrated network is observed. The resulting adsorption isotherms with one or two hysteresis loops are interpreted by a gate-opening process. Due to external stimuli, namely, the adsorptive pressure, the materials undergo a phase transition confirming the structural flexibility of the porous coordination polymer

Improved Isolation of Microbiologically Produced (2<i>R</i>,3<i>S</i>)‑Isocitric Acid by Adsorption on Activated Carbon and Recovery with Methanol

A new, efficient method for the isolation of (2<i>R</i>,3<i>S</i>)-isocitric acid (ICA) from its fermentation solution was developed. It is noteworthy that this method is based on selective adsorption directly from the fermentation solution on activated carbon, followed by the release of both ICA and citric acid by means of elution with methanol and their final separation by known methods. Thereby, several disadvantages were overcome: Electrodialysis is no longer necessary to remove cations such as Na⁺ from the fermentation solution. Also, several hitherto accompanying dyestuffs were not observed with this method. Furthermore, removal of water by distillation is expendable. Eventually, the new crude product is of a quality that also avoids the use of a tedious slide vane rotary vacuum pump distillation of the trimethyl esters of both acids, which hitherto was the basis for the separation of ICA. In summary, the new method distinctly spares energy as well as time

Platinum Group Metal Phosphides as Heterogeneous Catalysts for the Gas-Phase Hydroformylation of Small Olefins

A method for the synthesis of highly crystalline Rh₂P nanoparticles on SiO₂ support materials and their use as truly heterogeneous single-site catalysts for the hydroformylation of ethylene and propylene is presented. The supported Rh₂P nanoparticles were investigated by transmission electron microscopy and by infrared analysis of adsorbed CO. The influence of feed gas composition and reaction temperature on the activity and selectivity in the hydroformylation reaction was evaluated by using high throughput experimentation as an enabling element; core findings were that beneficial effects on the selectivity were observed at high CO partial pressures and after addition of water to the feed gas. The analytical and performance data of the materials gave evidence that high temperature reduction leading to highly crystalline Rh₂P nanoparticles is key to achieving active, selective, and long-term stable catalysts

Adsorption Measurements of Nitrogen and Methane in Hydrogen-Rich Mixtures at High Pressures

The separation of nitrogen and methane from hydrogen-rich mixtures is systematically investigated on a recently developed binder-free zeolite 5A. For this adsorbent, the present work provides a series of experimental data on adsorption isotherms and breakthrough curves of nitrogen and methane, as well as their mixtures in hydrogen. Isotherms were measured at temperatures of 283–313 K and pressures of up to 1.0 MPa. Breakthrough curves of CH4, N2, and CH4/N2 in H2 were obtained at temperatures of 300–305 K and pressures ranging from 0.1 to 6.05 MPa with different feed concentrations. An LDF-based model was developed to predict breakthrough curves using measured and calculated data as inputs. The number of parameters and the use of correlations were restricted to focus on the importance of measured values. For the given assumptions, the results show that the model predictions agree satisfactorily with the experiments under the different operating conditions applied