Unlocking the Separation Capacities of a 3D-Iron-Based Metal Organic Framework Built from Scarce Fe₄O₂ Core for Upgrading Natural Gas

Methane is an important alternative fuel, and upgrading it to improve fuel efficiency is an imperative target. Solid sorbents capable of selectively removing the major impurities CO2 and N2 from the natural gas contribute immensely to this process. We report a porous 3D iron-MOF built by linking scarce Fe4O18N2 clusters through readily available terephthalate and diaminotrizaole ligands. The 1-D channels with a high density of polarizing amine groups, aromatic rings, and carboxylate oxygen adsorb CO2 and the even less polarizable CH4. The MOF uptakes 4.7 mmol/g of CO2 at 273 K, 1 bar, with an optimal heat of adsorption of ≈24.5 kJ/mol and CO2/N2 IAST selectivity of ≈26. At higher pressures, the MOF exhibits a Langmuir type isotherm for methane and nitrogen with a CH4/N2 IAST selectivity of ≈4. The MOF’s excellent cyclic stability is affirmed by the TGA- and iso-cycling. Modeling studies propound the amine’s interactions with the CO2, but more dominant is the CO2···CO2 cooperative interactions. At 20 bar, CH4 interacts with many framework sites through weak dispersive interactions. In contrast, N2 interacts specifically with the triazole moiety; thus, the MOF favors the former. The CO2, CH4, and N2 diffusion coefficients, calculated using MD simulations, are quite favorable (Dc for CO2 = 1.11 × 10–6; CH4 = 9.04 × 10–6; N2 = 1.875 × 10–5 cm2/s). The dynamic breakthrough studies confirm the potential of the Fe-MOF to separate the gas mixtures. With these advantageous sorbent characteristics of this Fe-MOF, we propose using it in a two-stage PSA for the natural gas purification process, Stage I: removal of CO2 and Stage II: removal of N2. The outcomes point to the potential of a readily accessible iron-based amine MOF as sorbent for natural gas upgrading. A process optimization using a 4-step PSA validates the ability of our MOF to yield >96% purity of CH4 as required for pipeline transportation

COF-supported zirconium oxyhydroxide as a versatile heterogeneous catalyst for Knoevenagel condensation and nerve agent hydrolysis

Summary: A composite of catalytic Lewis acidic zirconium oxyhydroxides (8 wt %) and a covalent organic framework (COF) was synthesized. X-ray diffraction and infrared (IR) spectroscopy reveal that COF’s structure is preserved after loading with zirconium oxyhydroxides. Electron microscopy confirms a homogeneous distribution of nano- to sub-micron-sized zirconium clusters in the COF. 3D X-ray tomography captures the micron-sized channels connecting the well-dispersed zirconium clusters on the COF. The crystalline ZrOx(OH)y@COF’s nanostructure was model-optimized via simulated annealing methods. Using 0.8 mol % of the catalyst yielded a turnover number of 100–120 and a turnover frequency of 160–360 h−1 for Knoevenagel condensation in aqueous medium. Additionally, 2.2 mol % of catalyst catalyzes the hydrolysis of dimethyl nitrophenyl phosphate, a simulant of nerve agent Soman, with a conversion rate of 37% in 180 min. The hydrolytic detoxification of the live agent Soman is also achieved. Our study unveils COF-stabilized ZrOx(OH)y as a new class of zirconium-based Lewis + Bronsted-acid catalysts