Optimal Pore Chemistry in an Ultramicroporous Metal–Organic Framework for Benchmark Inverse CO₂/C₂H₂ Separation

Abstract

Isolation of CO 2 from acetylene (C 2 H 2 )v ia CO 2selective sorbents is an energy-efficient technology for C 2 H 2 purification, but as trategic challenge due to their similar physicochemical properties.T here is still no specific methodology for constructing sorbents that preferentially trap CO 2 over C 2 H 2 .W ereport an effective strategy to construct optimal pore chemistry in aC e IV -based ultramicroporous metalorganic framework Ce IV -MIL-140-4F,based on charge-transfer effects,f or efficient inverse CO 2 /C 2 H 2 separation. The ligandto-metal cluster charge transfer is facilitated by Ce IV with lowlying unoccupied 4f orbitals and electron-withdrawing Fatoms functionalizedt etrafluoroterephthalate,a ffording ap erfect pore environment to matchCO 2 .The exceptional CO 2 uptake (151.7 cm 3 cm À3 )along with remarkable separation selectivities (above4 0) set an ew benchmark for inverse CO 2 /C 2 H 2 separation, which is verified via simulated and experimental breakthrough experiments.The unique CO 2 recognition mechanism is further unveiled by in situ powder X-ray diffraction experiments,F ourier-transform infrared spectroscopym easurements,and molecular calculations.

Inverse CO2/C2H2 Separation with MFU‐4 and Selectivity Reversal via Postsynthetic Ligand Exchange

“…Activated MFU‐4 shows CO 2 uptake (3.17 mmol g −1 ) at 300 K and 1 bar and an isosteric enthalpy of CO 2 adsorption (Δ H ads =−24 kJ mol −1 ) that are consistent with previous reports (Figures S5 and S7) [21] . Notably, this Δ H ads is among the lowest reported for top‐performing adsorbents for inverse CO 2 /C 2 H 2 separation (Figure 2b and Table S1) [14, 15, 17, 23–27] . Among these, the CO 2 adsorption capacity of MFU‐4 at 1 bar is only surpassed by Ce IV ‐MIL‐140‐4F (4.9 mmol g −1 ) and Tm 2 (OH‐bdc) 2 (μ 3 ‐OH) 2 (H 2 O) 2 (5.8 mmol g −1 ), both of which exhibit a greater Δ H ads for CO 2 .…”

“…The ability of MFU‐4 to generate high purity C 2 H 2 (98–99 %) from equimolar CO 2 /C 2 H 2 mixtures in a single column adsorption step is notable given the paucity of MOFs reported to be capable of inverse CO 2 /C 2 H 2 separation [14, 15, 17, 23–27] . Moreover, to the best of our knowledge, there are only two previous reports of kinetically‐controlled inverse CO 2 /C 2 H 2 separation [17, 18] .…”

Metal‐Organic Frameworks for C6 Alkane Separation

“…Metal‐organic frameworks (MOFs) as a newer family of porous adsorbents are particularly desirable in addressing industrially challenging separations of hydrocarbons because of their diverse structural modularity, exceptional porosity, highly tunable pore size, pore shape, and surface functionality [15–18] . These unique features of MOFs have led to their excellent performance for the separation of physically and chemically similar mixtures including olefin/paraffin, [19–23] alkyne/olefin, [24, 25] carbon dioxide/acetylene, [26–28] and alkane isomers [29, 30] . In particular, the successful practice of reticular chemistry has enabled the precise control of pore structures of MOFs, affording adsorbents with desired discrimination capability toward C6 alkane isomers with different degrees of branching (Table 1).…”

Metal‐Organic Frameworks for C6 Alkane Separation

“…Metal‐organic frameworks (MOFs) as a newer family of porous adsorbents are particularly desirable in addressing industrially challenging separations of hydrocarbons because of their diverse structural modularity, exceptional porosity, highly tunable pore size, pore shape, and surface functionality [15–18] . These unique features of MOFs have led to their excellent performance for the separation of physically and chemically similar mixtures including olefin/paraffin, [19–23] alkyne/olefin, [24, 25] carbon dioxide/acetylene, [26–28] and alkane isomers [29, 30] . In particular, the successful practice of reticular chemistry has enabled the precise control of pore structures of MOFs, affording adsorbents with desired discrimination capability toward C6 alkane isomers with different degrees of branching (Table 1).…”