Ligand Tailoring Strategy of a Metal-Organic Framework for Optimizing Methane Storage Working Capacities

High-Capacity Volumetric Methane Storage in Hyper-Cross-Linked Porous Polymers via Flexibility Engineering of Building Units

Adsorbed natural gas (ANG) storage is emerging as a promising alternative to traditional compressed and liquefied storage methods. However, its onboard application is restricted by low volumetric methane storage capacity. Flexible porous adsorbents offer a potential solution, as their dense structures and unique gate-opening effects are well-suited to enhance volumetric capacity under high pressures. This study developes a series of hyper-cross-linked polymers (HCPs) with tunable flexibility by modifying the aliphatic chain length in double-benzene-ring building blocks, employing a cost-effective external crosslinking approach. The resulting flexible polymer, HCP-DPP, exhibits pore expansion under specific methane pressures, producing a high-pressure adsorption isotherm with gate-opening behavior. Combined with its intrinsic dense skeleton, this feature leads to superior volumetric methane storage performance over rigid counterparts. Notably, HCP-DPP achieves a record-high volumetric total uptake of 333 cm3 STP cm-3 and a working capacity of 291 cm3 STP cm-3 at 273 K and 100 bar, exceeding the U.S. Department of Energy (DOE) target of 263 cm3 STP cm-3. These findings lay a foundation for developing advanced flexible porous adsorbents for practical ANG applications.

Metal Doping to Control Gate Opening and Increase Methane Working Capacity in Isostructural Flexible Diamondoid Networks

Adsorbed natural gas (ANG) systems involve using porous materials to increase the working capacity and/or reduce the storage pressure compared to compressed natural gas (CNG). Flexible metal-organic materials (FMOMs) are particularly interesting in this context since their stepped isotherms can afford increased working capacity if the adsorption/desorption steps occur within the proper pressure range. We report herein that metal doping in a family of isostructural FMOMs, ML₂ (M=Co, Ni or Ni_x Co_1-x , L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), enables control over the gate opening between non-porous (closed) and porous (open) phases at pressures relevant to methane storage. Specifically, methane-induced phase transformations can be fine-tuned by using different Ni/Co ratios to enhance methane working capacity. The optimal working capacity from 5 to 35 bar at 298 K (153 cm³  cm^-3 ) was found for Ni_0.89 Co_0.11 L₂ (X-dia-1-Ni_0.89 Co_0.11 ), which is greater than that of benchmark rigid MOFs.

Theoretical investigation of C1-C4 hydrocarbons adsorption and separation in a porous metallocavitand

The purification of light hydrocarbons is one of the most important chemical processes globally which consumes substantial energy. Porous materials are likely to improve the efficiency of the separation process by acting as regenerable solid adsorbents. To investigate such translational systems, the underlying mechanism of adsorption in the porous materials must be taken into account. Herein we report the adsorption and selective separation of C1-C4 hydrocarbons in the coinage metal-based macrocyclic metallocavitand Pillarplex, which exhibits excellent performance in the adsorption of CH4 at the ambient conditions with a binding energy of -17.9 kcal mol-1. In addition, the endohedral adsorption of C2-C4 hydrocarbon is impressive. The CH4, C2H4, C3H4, and 1,3-butadiene have potential uptake of 2.57, 4.26, 3.60, and 2.95 mmol g-1, respectively at ambient conditions are highest from their respective isomers. Selective separation of C1-C4 hydrocarbons is studied using ideal adsorption solution theory demonstrating its potential for one-step purification of C1-C3 hydrocarbons.