Systemic regulation of binding sites in porous coordination polymers for ethylene purification from ternary C2 hydrocarbons

Abstract

The global demand for poly-grade ethylene (C₂H₄) is increasing annually. However, the energy-saving purification of this gas remains a major challenge due to the similarity in molecular properties among the ternary C2 hydrocarbons. To address this challenge, we report an approach of systematic tuning of the pore environment with organic sites (from –COOH to –CF₃, then to –CH₃) in porous coordination polymers (PCPs), of which NTU-73-CH₃ shows remarkable capability for the direct production of poly-grade C₂H₄ from ternary C2 hydrocarbons under ambient conditions. In comparison, the precursor structure of NTU-73-COOH is unable to purify C₂H₄, while NTU-73-CF₃ shows minimal ability to harvest C₂H₄. This is because the changed binding sites in the NTU-73-series not only eliminate the channel obstruction caused by the formation of gas clusters, but also enhance the interaction with acetylene (C₂H₂) and ethane (C₂H₆), as validated by in situ crystallographic and Raman analysis. Our findings, in particular the systematic tuning of the pore environment and the efficient C₂H₄ purification by NTU-73-CH₃, provide a blueprint for the creation of advanced porous families that can handle desired tasks.

---

Introduction

Ethylene (C₂H₄) is used as an important building block in industry for the production of value-added organics.^1–3 Currently, C₂H₄ is mainly obtained by separating the downstream of cracking of naphtha, C2 hydrocarbon gas mixtures during the steam cracking process.^4–6 Typically, acetylene (C₂H₂) is removed by solvent extraction or catalytic hydrogenation, which requires large equipment, as well as large amounts of solvents or higher temperature.^7,8 Subsequently, ethane (C₂H₆) is removed through cryogenic distillation, a type of huge energy-consuming process.⁹

The energy-intensive and cost-effective processes have spurred research into the development of energy-efficient approaches.¹⁰ Adsorptive separation, with a significant character of energy efficiency, has been considered as a kind of alternative or transition technology.¹¹ Porous coordination polymers (PCPs),^12–16 covalent organic frameworks (COFs),^17,18 zeolites,^19–21 and carbon materials²² have been explored for gas separation. Thanks to the rational pore tuning and straightforward pore functionalization, PCPs have shown good performance as adsorbents for various gas separations, but only a few examples can purify C₂H₄ from binary mixtures containing C₂H₂ or C₂H₆. However, from an energy point of view, it is crucial to remove both by-products in one-step with an adsorbent, but the challenge is enormous.^23–25

In general, the preferential adsorption of C₂H₂ over C₂H₄ requires the pore to contain highly polar sites (such as inorganic anionic pillars and open metal sites) due to the larger quadrupole moment (7.2 × 10⁻²⁶ vs. 1.5 × 10⁻²⁶ esu cm²) and higher acidity (pK_a: 45 vs. 26) of C₂H₂, resulting in strong host–C₂H₂ electrostatic interactions.²⁶ Conversely, the greater polarizability of C₂H₆ (44.7 × 10⁻²⁵ vs. 42.5 × 10⁻²⁵ cm³) contributes to the relatively weak van der Waals interactions with the structural framework modified low polarity sites.^27–30 To address this conflict, very few studies have been reported, primarily by exploiting the supramolecular interactions. The early framework of TJT-100 demonstrates the simultaneous capture of C₂H₂ and C₂H₆ through a hierarchy of interactions between the electronegative carboxylate O atoms and the gases.¹¹ A similar interaction has also been observed in NPU-1.³¹ By incorporating the –NH₂ group or exposing the N site, UiO-67-NH₂ and Al-PyDC also show preferential adsorption of C₂H₂ and C₂H_6.^32,33 Additionally, the cyclopentadiene-cobalt functional group in the UPC-series allows for efficient separation of C2 hydrocarbon mixtures. More promisingly, the synergistic sorbent separation technology (also called Lego-brick strategy) enables the production of high-purity C₂H₄ from a quaternary mixture of C₂H₆/C₂H₄/C₂H₂/CO₂ by utilizing tandem packing of carefully selected PCPs, with each PCP acting as a separator for binary mixtures.^25,34 Although these individual materials exhibit the desired functions, further systematic exploration is urgently needed due to the abundance and facile tunability of the supramolecular sites.

We are interested in the separation of light hydrocarbons using finely designed PCPs.^35–39 Recently, we have reported a new family of PCPs with crab-like carboxylic pincers, which allows for high C₂H₂/C₂H₄ selectivity and an unprecedented ability to obtain high-purity forms of both gases.⁴⁰ However, the strong binding interaction allows the absorbed C₂H₂ to form a tetrameric gas cluster at the channel neck, which strongly blocks the accessibility of the adjacent large cavity. Inspired by the unique porous nature of NTU-73 and also by the function of supramolecular sites, we report here a systematic tuning of functional sites in this porous platform, where the carboxylic pincers on the pore wall (corresponding L1: 3,5-di(1H-imidazol-1-yl)benzoic acid) were replaced with –CF₃ (corresponding L2: 1,1′-(5-(trifluoromethyl)-1,3-phenylene)bis(1H-imidazole)) or –CH₃ (corresponding L3: 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole)) (Scheme 1). The highly stable NTU-73-CH₃ exhibits a remarkable ability to directly produce poly-grade C₂H₄ from ternary C2 hydrocarbons, while, NTU-73-CF₃ and NTU-73-COOH can only exhibit minimal capacity or are unable to achieve C₂H₄ purification at all. These results reflect the positive effect of changing functional sites on strengthening the host–guest interactions and the stability of the framework.

Scheme 1 Systemic tuning of the functional sites in PCPs for efficient C₂H₄ purification.

Experimental section

General procedures of the experiments and simulation are available in the ESI.†

Synthesis of NTU-73-series

Synthesis of NTU-73-COOH. NTU-73-COOH was synthesized according to our previous work.⁴⁰

Synthesis of NTU-73-CF₃. Cu(BF₄)₂·6H₂O (10 mg, 0.039 mmol), L2 (5 mg, 0.018 mmol) and H₂ZrF₆ (50 μL, 45%) were mixed in N,N′-dimethylacetamide (DMA)/H₂O/ethanol (EtOH) (0.5/0.25/0.75, v/v/v, 1.5 mL) and reacted at 90 °C for 2 days to obtain blue block crystals. After cooling down, the crystals were washed three times with fresh DMA (yield: ∼52%, based on L2).

Synthesis of NTU-73-CH₃. Cu(BF₄)₂·6H₂O (10 mg, 0.039 mmol), L3 (5 mg, 0.022 mmol) and H₂ZrF₆ (50 μL, 45%) were added to the DMA/H₂O/EtOH (0.5/0.25/0.75, 1.5 mL) mixed solvent and reacted at 90 °C for 2 days to give blue block crystals. After cooling down, the crystals were washed three times with fresh DMA (yield: ∼60%, based on L3).

Results and discussion

Crystal structures and characterization

Solvent-thermal reactions of copper(II) hexafluorozirconium with corresponding ligands yielded polyhedron-shaped crystals (NTU-73-series). These crystals all crystallized in a tetragonal I4₁22 space group with the formula of [Cu(L)₂ZrF₆]·xGuest (Table S1†). Two of our newly synthesized crystals (NTU-73-CF₃ and NTU-73-CH₃) have the same coordination mode as that of NTU-73-COOH. The asymmetric unit of all three PCPs consists of one ligand, half a Cu²⁺ ion and half a ZrF₆²⁻ anion. Each Cu node is coordinated by two F atoms from the two ZrF₆²⁻ anions and four imidazole N atoms from four ligands (Fig. S3–S5†). Additionally, two helical chains linked by ZrF₆²⁻ anions are present in the frameworks (Fig. S6†). Differently, the carboxylic-modified channel wall observed from two different directions in NTU-73-COOH has been replaced by a couple of –CF₃ or –CH₃ groups in NTU-73-CF₃ and NTU-73-CH₃ (Fig. S7–S12†), respectively. Furthermore, there is an overall trend of increasing pore size (NTU-73-COOH: 4.5 × 5.2 Ų and 3.9 × 5.6 Ų; NTU-73-CF₃: 3.7 × 5.2 Ų and 4.2 × 7.8 Ų; NTU-73-CH₃: 4.4 × 5.4 Ų and 6.2 × 9.2 Ų) as the functional group size gradually decreases (Fig. 1). Considering the unique ability of NTU-73-COOH to separate C₂H₂/C₂H₄ and the systematic changes in the pore environment, including binding sites and pore size, we expected this platform to be highly efficient for the C2 ternary mixture separation. The phase purity of the crystals was confirmed by powder X-ray diffraction (PXRD) as the diffraction peaks of the synthesized and activated NTU-73-series were in good agreement with the simulated patterns (Fig. S13–S15†).

Fig. 1 Structure of the NTU-73-series: local views of the nanospace of NTU-73-COOH (a and d), NTU-73-CF₃ (b and e) and NTU-73-CH₃ (c and f) in different directions.

Pore evaluation

The permanent porosity of the NTU-73-series was investigated through N₂ (77 K) and CO₂ (195 K) adsorption measurements (Fig. 2a and S22†). Although NTU-73-COOH exhibits negligible N₂ uptake, the two newly prepared PCPs show improved N₂ adsorption, with maximum uptakes of 193 and 295 cm³ g⁻¹, respectively. Interestingly, all three PCPs show type-I and significant CO₂ adsorption isotherms. The maximum uptake increases from 63 (NTU-73-COOH) to 250 cm³ g⁻¹ (NTU-73-CH₃). For consistency, the Brunauer–Emmett–Teller surface areas of the NTU-73-series were calculated based on CO₂ isotherms. The BET surface areas of the NTU-73-series were calculated to be 228, 889 and 1078 m² g⁻¹, respectively, with corresponding pore volumes of 0.039, 0.153 and 0.185 m³ g⁻¹ (Table S2†). Additionally, the pore size distribution is consistent with the crystal structures, verifying the impact of the functional groups on pore size tuning (Fig. S23†).

Fig. 2 CO₂-adsorption isotherms of the NTU-73-series at 195 K (a). C₂H₄ and C₂H₆ adsorption isotherms of NTU-73-COOH (b), NTU-73-CF₃ (c), and NTU-73-CH₃ (d) at 298 K. Uptake difference (e) and isosteric heats (f) of the three PCPs.

Single-component adsorption and selectivity

Single-component adsorption isotherms of C₂H₂, C₂H₄ and C₂H₆ were collected for the three PCPs (Fig. 2b–d and S24–S35†), respectively. With the carboxylate pincers, exposed in the nanochannel, NTU-73-COOH shows the lowest gas uptake (C₂H₂: 32.3 cm³ g⁻¹, C₂H₄: 12.9 cm³ g⁻¹ and C₂H₆: 11.8 cm³ g⁻¹) among the three PCPs. Not only that, the adsorption capacity of C₂H₄ is slightly higher than that of C₂H₆, indicating an impossible harvesting of pure C₂H₄ in one-step from the ternary C2 mixtures, although it shows promising ability in binary C₂H₂/C₂H₄ separation. After replacing the –COOH groups with –CF₃ groups, NTU-73-CF₃ shows a significantly increased gas uptake at 100 kPa (C₂H₂: 77.7 cm³ g⁻¹, C₂H₄: 62.0 cm³ g⁻¹, and C₂H₆: 62.7 cm³ g⁻¹), in which the C₂H₆ uptake is slightly higher than that of C₂H₄. Comparing the structural nature of the above two, the decrease in the polarity of the pore surface could alter the sequence of host–C₂H₄ and –C₂H₆ interactions. As expected, the adsorption capacities of C2 gases show a further increase in NTU-73-CH₃ (C₂H₂: 98.0 cm³ g⁻¹; C₂H₄: 77.8 cm³ g⁻¹; C₂H₆: 89.9 cm³ g⁻¹), particularly, the C₂H₆ uptake is higher than that of C₂H₄ (12.1 cm³ g⁻¹, 100 kPa, 298 K). Notably, this uptake difference is much higher than that of the benchmark materials of MOF-303 (−0.5 cm³ g⁻¹),⁴¹ NPU-1 (6.7 cm³ g⁻¹),³¹ TJT-100 (5.8 cm³ g⁻¹),¹¹ and is approaching that of Al-PyDC (17.0 cm³ g⁻¹, 296 K)³³ and UPC-612 (17.5 cm³ g⁻¹)⁶ (Table S3†). In addition, despite the gradual decrease in pore channel polarity, C₂H₂ uptake is always higher than that of C₂H₄, about 20.0 cm³ g⁻¹, in the NTU-73-series (Fig. 2e and S36†). In other words, systematically tuned organic sites endow significant functional changes, where NTU-73-CH₃ is expected to achieve efficient C₂H₄ purification from C2 ternary mixtures.

Static adsorption selectivity and isosteric heats

To further evaluate the gas separation performance, the adsorption selectivities of C₂H₆/C₂H₄ and C₂H₂/C₂H₄ at 298 K were calculated via the ideal adsorbed solution theory (IAST) after fitting the single-component adsorption isotherms to the Langmuir–Freundlich equation (Fig. S37–S49†). For the equimolar C₂H₆/C₂H₄ mixtures, the adsorption selectivity values were found to be 0.66 for NTU-73-COOH, 1.18 for NTU-73-CF₃ and 1.33 for NTU-73-CH₃. Importantly, the selectivity of NTU-73-CH₃ is higher than that of TJT-100 (1.2) and NPU-1 (1.32), and close to that of UPC-612 (1.4), MOF-303 (1.7), Al-PyDC (1.9, 296 K) under almost the same conditions (Table S3†). Additionally, among the top-tier (C₂H₆–C₂H₄ uptake difference larger than 10 cm³ g⁻¹) C₂H₂–C₂H₆-selective adsorbents, the C₂H₂/C₂H₄ (1/99, v/v) selectivity (3.2 at 298 K, 100 kPa) of NTU-73-CH₃ is only lower than that of Al-PyDC (4.3 at 296 K, 100 kPa) (Table S4†). Therefore, the high C₂H₆–C₂H₄ uptake difference and the good selectivities make NTU-73-CH₃ a promising candidate for C₂H₄ purification from C2 ternary mixtures.

To evaluate the interaction strength of C₂H₂, C₂H₄ and C₂H₆ in the NTU-73-series, the isosteric heat (Q_st) was calculated after fitting the adsorption isotherms by the virial equation at 273, 283 and 298 K, respectively (Fig. 2f and S50–S59†). The Q_st value of C₂H₂ (NTU-73-COOH: 41.00 kJ mol⁻¹, NTU-73-CF₃: 39.83 kJ mol⁻¹, NTU-73-CH₃: 37.06 kJ mol⁻¹) is higher than that of C₂H₄ (NTU-73-COOH: 35.78 kJ mol⁻¹, NTU-73-CF₃: 32.12 kJ mol⁻¹, NTU-73-CH₃: 29.90 kJ mol⁻¹) and C₂H₆ (NTU-73-COOH: 26.10 kJ mol⁻¹, NTU-73-CF₃: 32.39 kJ mol⁻¹, NTU-73-CH₃: 35.43 kJ mol⁻¹) in the NTU-73-series at low coverage, while an inversion of the host–C₂H₄ and host–C₂H₆ interactions was observed: a higher Q_st of C₂H₄ over C₂H₆ in NTU-73-COOH changes to a higher Q_st of C₂H₆ over C₂H₄ in NTU-73-CH₃. These observations are consistent with the adsorption isotherms. In addition, these relatively low adsorption enthalpy values indicate a relatively low energy consumption for regeneration of the PCPs.

Gas-loaded crystallographic and Raman analysis

The isosteric heat is a kind of statistical result, making it difficult to accurately describe the role of functional sites. Therefore, to better explore the reversal phenomenon of C₂H₄ and C₂H₆ adsorption and Q_st values, gas-loaded crystallographic analysis was performed at 298 K (Fig. 3 and Table S5†).⁴² Despite the disordered nature, the trapped gases can be clearly found in these three PCPs. For NTU-73-COOH⊃C₂H₄, two C₂H₄ molecules form three hydrogen bonds with the O_COOH of the free carboxylic pincers, of which, the shortest distance is 1.8973 Å. Meanwhile, intermolecular interactions (dC_C2H4–H⋯C_C2H4: 2.3748 to 2.8025 Å) have been found between these two molecules (Fig. 3a). For NTU-73-COOH⊃C₂H₆, two groups of hydrogen bonds (dC_C2H6–H⋯O_COOH: 2.3338 to 2.9779 Å and g C_C2H6–H⋯N_imidazole) with relatively longer distances were observed. In addition, the slightly larger distance leads to the disappearance of the intermolecular interactions (Fig. 3b). This clear change can therefore explain the fact that NTU-73-COOH binds C₂H₄ more strongly than C₂H₆. However, in contrast to our expectation, the distance between the gases and the –CF₃ group is relatively far. So as that, both molecules are located around the coordinated ZrF₆²⁻ ions. This is due to the relatively weak degree of electronegativity of F_CF3 compared to that of F_ZrF6. However, the presence of the –CF₃ group influences the configuration of the adsorbed gas molecules. As can be seen, the two F atoms of ZrF₆²⁻ form two hydrogen bonds with C₂H₄ and C₂H₆, respectively. The shortest distances of the hydrogen bonds (dC_C2H6–H⋯F_ZrF6: 2.6094 Å and dC_C2H4–H⋯F_ZrF6: 2.6647 Å) are very close to each other, indicating similar host–guest interactions (Fig. 3c and d). In NTU-73-CH₃, both gases are also observed around the coordinated ZrF₆²⁻ ions. Without the withdrawal effect of the organic F sites from –CF₃, the configuration of the adsorbed C₂H₄ shows a slight change, wherein the distance of the two hydrogen bonds (C_C2H4–H⋯F_ZrF6) becomes close to each other (2.9352 Å and 2.9775 Å) (Fig. 3e). Additionally, the end-on mode of C_C2H6–H⋯F_ZrF6 in NTU-73-CF₃ changes to a chelate connection in NTU-73-CH₃; particularly, the distance of the two C_C2H6–H⋯F_ZrF6 (2.1757 Å and 2.3150 Å) is shorter than that of C_C2H4–H⋯F_ZrF6 in NTU-73-CF₃ (Fig. 3f). Therefore, these results not only explain the phenomenon of the adsorption trend of C₂H₄ and C₂H₆ in NTU-73-series, but also can strengthen the molecular insights of fine-tuning the pore environment by functional organic groups.

Fig. 3 C₂H₄- and C₂H₆-loaded crystallographic analysis of NTU-73-COOH (a and b), NTU-73-CF₃ (c and d) and NTU-73-CH₃ (e and f).

Given the promising nature of NTU-73-CH₃, the stabilizing effect of the pore environment towards C₂H₄ and C₂H₆ was further evaluated by Raman spectra. After dosing a highly pure gas (He, C₂H₄ or C₂H₆, 1 bar, 298 K) into the glass tube with fully activated NTU-73-CH₃, respectively, the corresponding spectra were recorded in the range of 1000 to 4000 cm⁻¹ (Fig. 4 and S60†). As can be seen, the peaks at 2887 cm⁻¹ and 2942 cm⁻¹ belonging to the stretching vibration of C₂H₆ have been identified,⁴³ but no additional peaks other than those belonging to NTU-73-CH₃ were observed under the C₂H₄ atmosphere (theoretical position: 1689 cm⁻¹). Therefore, it is clear that NTU-73-CH₃ not only has a relatively stronger host–C₂H₆ interaction, but also can stabilize a certain number of C₂H₆ molecules in a periodic arrangement, which is consistent with the results of the crystallographic analysis.

Fig. 4 Raman spectra of gas-loaded NTU-73-CH₃ (the peaks marked with * derived from the framework).

Breakthrough experiments

To validate the separation performance under dynamic conditions, breakthrough experiments were conducted on the NTU-73-series (Fig. 5 and S61–S69†). All initially activated samples were loaded into the column and further activation was achieved by He sweeping until no signals were detected. Breakthrough experiments were then carried out using a binary mixture of C₂H₂/C₂H₄ (1 : 99, v/v) at first, a typical industrial composition. Compared to NTU-73-COOH, both NTU-73-CF₃ and NTU-73-CH₃ showed a certain loss of breakthrough time interval, but still demonstrated the separation ability towards C₂H₂/C₂H₄. Further experiments were conducted on C₂H₆/C₂H₄ mixtures. At a volume ratio of 1 : 15, C₂H₆ breaks through slightly earlier than C₂H₄ for the NTU-73-COOH sample bed. Interestingly, high purity C₂H₄ can be obtained directly at the outlet of the NTU-73-CF₃ and NTU-73-CH₃ columns, of which, NTU-73-CH₃ has a longer C₂H₆–C₂H₄ breakthrough interval than NTU-73-CF₃ (4.8 min g⁻¹ vs. 4.0 min g⁻¹). To further investigate the influence of ratio on this separation, a feed gas with a ratio of 1 : 9, the most common ratio found in the cracking process, was introduced into the column. NTU-73-COOH was unable to separate this mixture, while NTU-73-CF₃ and NTU-73-CH₃ retained their separation abilities. Among them, NTU-73-CH₃ showed the longest breakthrough time interval (4.6 min g⁻¹ vs. 2.7 min g⁻¹ vs. 0 min g⁻¹), owing to its higher selectivity for C₂H₆/C₂H₄ and its greater uptake capacity for C₂H₆ (Fig. 5a–c). This trend was also observed in experiments using equimolar C₂H₆/C₂H₄ mixtures.

Fig. 5 Experimental breakthrough curves of NTU-73-COOH (a and d), NTU-73-CF₃ (b and e), and NTU-73-CH₃ (c and f) for C₂H₆/C₂H₄ (1/9, v/v, 2 mL min⁻¹) and C₂H₂/C₂H₆/C₂H₄ (1/9/90, v/v/v, 2 mL min⁻¹) mixtures, respectively at 298 K. The gas pressure is 1.4 bar for all experiments.

Encouraged by the successful separation of the binary mixtures, C₂H₂/C₂H₄ and C₂H₆/C₂H₄, the separation ability of the NTU-73-series towards ternary mixtures C₂H₂/C₂H₆/C₂H₄ (1/9/90, v/v/v) was further investigated, respectively. As expected, both C₂H₆ and C₂H₄ elute out simultaneously from the NTU-73-COOH bed (Fig. 5d). Despite the separation potential, high-yield C₂H₄ cannot be produced by NTU-73-CF₃ (Fig. 5e). Only NTU-73-CH₃ allows significant production of high purity (>99.9%) C₂H₄ (0.52 mmol g⁻¹ (STP)) (Fig. 5f and S70†). This value is higher than that of CAU-23 (0.18 mmol g⁻¹), TJT-100 (0.41 mmol g⁻¹), and UPC-612 (0.47 mmol g⁻¹), but lower than that of MOF-303 (1.35 mmol g⁻¹) and Azole-Th-1 (1.34 mmol g⁻¹) (Tables S3 and S4†).

Stability and recyclability

Stability is another crucial factor in measuring the performance of adsorbents.⁴⁴ The crystals of NTU-73-COOH, NTU-73-CF₃ and NTU-73-CH₃ were immersed in chemical solutions (pH = 2, pH = 7 and pH = 12) for 3 days or exposed to air for 7 days, respectively. The PXRD patterns of the samples were then collected and compared with the simulated patterns (Fig. S71–S73†). The results reveal that some of the characteristic peaks of NTU-73-COOH and NTU-73-CF₃ were weakened or disappeared after immersion in certain solutions, in particular, the diffraction peaks almost completely disappeared in the alkaline solution (pH = 12), suggesting the structural instability. However, the crystals of NTU-73-CH₃ retained almost the same diffraction peaks after treatment under these harsh conditions. Additionally, the C₂H₆ uptakes of these treated samples are nearly the same (Fig. S74†), indicating that the introduction of the hydrophobic –CH₃ group plays a crucial role in protecting the coordination bonds and then stabilizing the framework. Thanks to this good stability, NTU-73-CH₃ demonstrates no loss of performance during the cycling breakthrough experiments (Fig. S75†).

Conclusions

In response to the demand for C₂H₄ purification, we herein report an approach of systematic tuning of the porous environment with organic sites (from –COOH to –CF₃ and then to –CH₃) in PCPs, wherein the highly stable NTU-73-CH₃ exhibits remarkable capability for direct production of poly-grade C₂H₄ from ternary C2 hydrocarbons under ambient conditions. In addition, the molecular insights derived from in situ crystallographic and Raman analysis confirm the positive effect of the –CH₃ group in tuning the configuration and strength of the adsorbed C₂H₄ and C₂H₆. This study not only highlights the importance of systemic regulation, but also illustrates how changes in functional groups within PCPs can profoundly affect the host–guest interaction and separation performance. Moreover, the strategy of systematic organic functionalization can be extended to other porous families, offering a powerful tool for tailoring high-performance PCPs for desired applications.

Data availability

All data can be found in the main text and ESI.†

Author contributions

J. D. and W. J. conceived the idea of this work. Y. L. carried out the experiments and analyzed the results. J. D. and Y. L. wrote the paper. All authors gave valuable suggestions for the final draft.

Conflicts of interest

The authors declare no competing interests.

Acknowledgements

We are thankful for the financial support of the National Natural Science Foundation of China (22171135), the National Natural Science Foundation of Jiangsu Province (BK20231269) and the State Key Laboratory of Materials-Oriented Chemical Engineering (SKL-MCE-23A18).

References

1. S. Gong, C. Shao and L. Zhu, Energy, 2021, 217, 119401.
2. S. M. Sadrameli, Fuel, 2016, 173, 285–297.
3. G. D. Wang, Y. Z. Li, W. J. Shi, L. Hou, Y. Y. Wang and Z. Zhu, Angew. Chem., Int. Ed., 2022, 61, e202205427.
4. Z. B. Bao, D. Y. Xie, G. G. Chang, H. Wu, L. Y. Li, W. Zhou, H. L. Wang, Z. G. Zhang, H. B. Xing, Q. W. Yang, M. J. Zaworotko, Q. L. Ren and B. L. Chen, J. Am. Chem. Soc., 2018, 140, 4596–4603.
5. Q. Ding, Z. Zhang, Y. Liu, K. Chai, R. Krishna and S. Zhang, Angew. Chem., Int. Ed., 2022, 61, e202208134.
6. Y. T. Wang, C. L. Hao, W. D. Fan, M. Y. Fu, X. K. Wang, Z. K. Wang, L. Zhu, Y. Li, X. Q. Lu, F. N. Dai, Z. X. Kang, R. M. Wang, W. Y. Guo, S. Q. Hu and D. F. Sun, Angew. Chem., Int. Ed., 2021, 60, 11350–11358.
7. F. Studt, F. Abild-Pedersen, T. Bligaard, R. Z. Sorensen, C. H. Christensen and J. K. Norskov, Science, 2008, 320, 1320–1322.
8. Z. Xu, X. Xiong, J. Xiong, R. Krishna, L. Li, Y. Fan, F. Luo and B. Chen, Nat. Commun., 2020, 11, 3163–3172.
9. K. Z. Su, W. J. Wang, S. F. Du, C. Q. Ji and D. Q. Yuan, Nat. Commun., 2021, 12, 3703–3710.
10. J.-W. Cao, S. Mukherjee, T. Pham, Y. Wang, T. Wang, T. Zhang, X. Jiang, H.-J. Tang, K. A. Forrest, B. Space, M. J. Zaworotko and K.-J. Chen, Nat. Commun., 2021, 12, 6507–6515.
11. H. G. Hao, Y. F. Zhao, D. M. Chen, J. M. Yu, K. Tan, S. Q. Ma, Y. Chabal, Z. M. Zhang, J. M. Dou, Z. H. Xiao, G. Day, H. C. Zhou and T. B. Lu, Angew. Chem., Int. Ed., 2018, 57, 16067–16071.
12. Z. Q. Zhang, S. B. Peh, Y. X. Wang, C. J. Kang, W. D. Fan and D. Zhao, Angew. Chem., Int. Ed., 2020, 59, 18927–18932.
13. S. H. Yang, A. J. Ramirez-Cuesta, R. Newby, V. Garcia-Sakai, P. Manuel, S. K. Callear, S. I. Campbell, C. C. Tang and M. Schroder, Nat. Chem., 2015, 7, 121–129.
14. P. Q. Liao, W. X. Zhang, J. P. Zhang and X. M. Chen, Nat. Commun., 2015, 6, 8697–8706.
15. C. Gu, N. Hosono, J. J. Zheng, Y. Sato, S. Kusaka, S. Sakaki and S. Kitagawa, Science, 2019, 363, 387–391.
16. Q. Ding, Z. Q. Zhang, C. Yu, P. X. Zhang, J. Wang, X. L. Cui, C. H. He, S. G. Deng and H. B. Xing, Sci. Adv., 2020, 6, 122617.
17. C. H. He, Y. Wang, Y. Chen, X. Q. Wang, J. F. Yang, L. B. Li and J. P. Li, ACS Appl. Mater. Interfaces, 2020, 12, 52819–52825.
18. L. C. Jiang, Y. Y. Tian, T. Sun, Y. L. Zhu, H. Ren, X. Q. Zou, Y. H. Ma, K. R. Meihaus, J. R. Long and G. S. Zhu, J. Am. Chem. Soc., 2018, 140, 15724–15730.
19. Y. Z. Liu, Y. Wu, W. W. Liang, J. J. Peng, Z. Li, H. H. Wang, M. J. Janik and J. Xiao, Chem. Eng. Sci., 2020, 220, 115636.
20. P. J. Bereciartua, A. Cantin, A. Corma, J. L. Jorda, M. Palomino, F. Rey, S. Valencia, E. W. Corcoran, P. Kortunov, P. I. Ravikovitch, A. Burton, C. Yoon, Y. Wang, C. Paur, J. Guzman, A. R. Bishop and G. L. Casty, Science, 2017, 358, 1068–1071.
21. Y. C. Chai, X. Han, W. Y. Li, S. S. Liu, S. K. Yao, C. Wang, W. Shi, I. Da-Silva, P. Manuel, Y. Q. Cheng, L. D. Daemen, A. J. Ramirez-Cuesta, C. C. Tang, L. Jiang, S. H. Yang, N. J. Guan and L. D. Li, Science, 2020, 368, 1002–1006.
22. W. W. Liang, Y. Wu, H. Y. Xiao, J. Xiao, Y. W. Li and Z. Li, Chem.–Eur. J., 2018, 64, 3390–3399.
23. C. Xiao, J. D. Tian, Q. H. Chen and M. C. Hong, Chem. Sci., 2024, 15, 1570–1610.
24. P. Zhang, Y. Zhong, Y. Zhang, Z. Zhu, Y. Liu, Y. Su, J. Chen, S. Chen, Z. Zeng, H. Xing, S. Deng and J. Wang, Sci. Adv., 2022, 8, eabn9231.
25. K. J. Chen, D. G. Madden, S. Mukherjee, T. Pham, K. A. Forrest, A. Kumar, B. Space, J. Kong, Q. Y. Zhang and M. J. Zaworotko, Science, 2019, 366, 241–246.
26. Q. Ding, Z. Q. Zhang, Y. L. Liu, K. G. Chai, R. Krishna and S. Zhang, Angew. Chem., Int. Ed., 2022, 61, e202208134.
27. M. Kang, S. Yoon, S. Ga, D. W. Kang, S. Han, J. H. Choe, H. Kim, D. W. Kim, Y. G. Chung and C. S. Hong, Adv. Sci., 2021, 8, 2004940.
28. M. J. Kang, D. W. Kang, J. H. Choe, H. Kim, D. W. Kim, H. Park and C. S. Hong, Chem. Mater., 2021, 33, 6193–6199.
29. J. Y. Pei, J. X. Wang, K. Shao, Y. Yang, Y. J. Cui, H. Wu, W. Zhou, B. Li and G. D. Qian, J. Mater. Chem. A, 2020, 8, 3613–3620.
30. R. B. Lin, H. Wu, L. B. Li, X. L. Tang, Z. Q. Li, J. K. Gao, H. Cui, W. Zhou and B. L. Chen, J. Am. Chem. Soc., 2018, 140, 12940–12946.
31. B. Y. Zhu, J. W. Cao, S. Mukherjee, T. Pham, T. Zhang, T. Wang, X. Jiang, K. A. Forrest, M. J. Zaworotko and K. J. Chen, J. Am. Chem. Soc., 2021, 143, 1485–1492.
32. X. W. Gu, J. X. Wang, E. Y. Wu, H. Wu, W. Zhou, G. D. Qian, B. L. Chen and B. Li, J. Am. Chem. Soc., 2022, 144, 2614–2623.
33. E. Wu, X.-W. Gu, D. Liu, X. Zhang, H. Wu, W. Zhou and G. Qian, Nat. Commun., 2023, 14, 6146–6157.
34. H. R. Sun, F. Q. Chen, R. D. Chen, J. Q. Li, L. D. Guo, Y. Liu, F. X. Shen, Q. W. Yang, Z. G. Zhang, Q. L. Ren and Z. B. Bao, Small, 2023, 19, 2208182.
35. Q. Dong, X. Zhang, S. Liu, R. B. Lin, Y. Guo, Y. Ma, A. Yonezu, R. Krishna, G. Liu, J. Duan, R. Matsuda, W. Jin and B. Chen, Angew. Chem., Int. Ed., 2020, 59, 22756–22762.
36. Q. Dong, Y. Huang, K. Hyeon-Deuk, I. Y. Chang, J. Wan, C. Chen, J. Duan, W. Jin and S. Kitagawa, Adv. Funct. Mater., 2022, 32, 2203745.
37. Y. Huang, J. Wan, T. Pan, K. Ge, Y. Guo, J. Duan, J. Bai, W. Jin and S. Kitagawa, J. Am. Chem. Soc., 2023, 145, 24425–24432.
38. J. Wan, H. L. Zhou, K. Hyeon-Deuk, I. Y. Chang, Y. Huang, R. Krishna and J. Duan, Angew. Chem., Int. Ed., 2023, 62, e202316792.
39. H. Wang, Y. Duan, Y. Wang, Y. Huang, K. Ge, S. Wang, B. Zheng, Z. Wang, J. Bai and J. Duan, ACS Appl. Mater. Interfaces, 2022, 14, 13550–13559.
40. Y. F. Duan, Y. H. Huang, C. Q. Wang, Q. Wang, K. Ge, Z. Y. Lu, H. J. Wang, J. G. Duan, J. F. Bai and W. Q. Jin, Chem. Sci., 2023, 14, 4605–4611.
41. H.-M. Wen, C. Yu, M. Liu, C. Lin, B. Zhao, H. Wu, W. Zhou, B. Chen and J. Hu, Angew. Chem., Int. Ed., 2023, 62, e202309108.
42. Q. Dong, Y. Huang, J. Wan, Z. Lu, Z. Wang, C. Gu, J. Duan and J. Bai, J. Am. Chem. Soc., 2023, 145, 8043–8051.
43. R. Fantoni, K. Vanhelvoort, W. Knippers and J. Reuss, Chem. Phys., 1986, 110, 1–16.
44. Q. B. Dong, J. M. Wan, H. H. Chen, Y. H. Huang and J. G. Duan, ACS Appl. Mater. Interfaces, 2023, 15, 39606–39613.

---

Footnote

† Electronic supplementary information (ESI) available: Synthesis and characterization of the three crystals, PXRD, TGA, IR, sorption isotherms, IAST, breakthrough experiments and fitting parameters. CCDC 2337168–2337175. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4sc02659d

---