As the result of rapid urbanization, industrialization, and human population growth, the consumption of fossil fuels has been increasing constantly and swiftly. Natural gas is one of the most commonly used energy sources not only due to its abundant reserves in nature but also because it is more eco-friendly compared to oil and coal[1–2]. Generally, besides CH₄ as the main component, C₂H₆ (0–20%) and C₃H₈ (0–5%) coexist in the natural gas and should be fully recovered individually for updating the quality of natural gas. Subsequently, the recovered C₂H₆ and C₃H₈ can be utilized to produce C₂H₄ and C₃H₆ through catalytic dehydrogenation, which are the raw materials for producing various plastics, such as polyethylene, poly (vinyl chloride), and polypropylene[3–5]. Traditional cryogenic distillation has shown excellent performance in industrial separation processes but it is operated under high pressure and/or low temperature, leading to high energy-consumption[6–7]. Among the newly developed separation methods, adsorptive separation technology has been regarded as a promising alternative to cryogenic distillation because of its high separation efficiency and low energy input [8,9]. The applicability of adsorptive separation is largely dependent on the performance of adsorbents, which involves their porosity, pore dimensions, and pore surface functionality.

Metal–organic frameworks (MOFs) represent an emerging class of porous materials assembled from metal centers and organic ligands through coordination bonds, which have drawn tremendous attention in the field of gas separation, due to their intrinsic advantages including extra-high surface area, structural diversity, pore tunability, and controllable functionality[10–14]. While MOFs have shown encouraging potential in the separation and recovery of C₂H₆ and C₃H₈ from natural gas, there still exist several problems that need to be addressed. First, the uptake capacity of C₂H₆ and C₃H₈ at low pressure is still not sufficient. For example, boron cage pillared supramolecular metal–organic framework (BSF)-2 possesses a very high selectivity but the equilibrium uptake amounts of C₃H₈ and C₂H₆ are only 1.77 and 1.22 mmol·g^–1 , respectively, leading to low separation efficiency [15]. Matériaux de l’Institut Lavoisier (MIL)-100(Fe) exhibits high uptake capacity of C₂H₆ and C₃H₈ at 1 bar (1 bar = 10⁵ Pa) but the values are too low at low pressure [16]. As a result, these MOFs show limited applicability due to the low C₂H₆ and C₃H₈ concentrations in nature gas. Low stability of most reported MOFs in the presence of moisture is the second problem. For example, MOF-74 and Hong Kong University of Science and Technology (HKUST)-1 feature high separation capability but suffer from structural decomposition in humid air[17,18]. High moisture stability is essential for an adsorbent to be used in nature gas purification because the gas mixture always contains a certain amount of water vapor[19–22]. In addition, material cost and scale-up capability are also important factors in determining the feasibility for industrial applications. While some MOFs show high performance and sufficient water/- moisture stability, such as Ni(TMBDC)(DABCO)_0.5 (TMBDC: 2,3,5,6-tetramethylterephthalic acid; DABCO: 1,4-diazabicyclo [2.2.2]octane) [23] and Fujian Institute of Research on the Structure of Matter (FJI)-C4 [7], they are constructed from expensive organic linkers which would seriously hinder their industrial utility when considering the economic feasibility. MOFs synthesized in relative harsh conditions involving high temperature, high pressure, large amounts of template, or complex steps are usually difficult to scale up[24,25]. Hence, developing or screening ideal MOF adsorbents for targeted industrial applications require consideration of all these aspects in order to reach an optimal balance between separation performance, stability, and cost. 

To improve the uptake of C₂H₆ and C₃H₈ at low pressure, we propose an effective strategy based on our previous study: simultaneously enhancing the polarity of the pore surface and tuning the pore diameter to a suitable size (Fig. 1). On one hand, increasing surface polarity by introducing polar atoms or functional groups could markedly strengthen the interaction between gas molecules and MOFs as the C–H bond in hydrocarbons preferentially binds to the polar atoms or functional groups through hydrogen bonds[11,26,27]. On the other hand, a suitable pore size is very crucial because the diffusion of C₃H₈ molecules would be seriously restricted if pore is too narrow, and on the contrary, a larger pore always causes weaker interaction, leading to unsatisfactory uptake capacity and selectivity, especially at low pressure. We could envision that suitable pore diameter and highly polar surface simultaneously existing in a MOF could concurrently reinforce multiple hydrogen bonds, resulting in significant enhancement in high adsorption capacity and selectivity. As to moisture stability, MOFs built on metals with high valence such as Zr⁴⁺, Cr³⁺, and Al³⁺ are generally resistant to water[28–32]. Finally, using MOFs with inexpensive ligands and high scale-up ability can lower the total cost and significantly enhance their likelihood for industrial applications. 

Fig. 1. Schematic illustration on how highly polar surface and suitable pore diameter of a MOF may synergistically enhance the affinity of the framework toward C₃H₈ to result in a highly efficient separation of C₃H₈ and CH₄.

MOF-303 and MIL-160 are selected in this work when taking all these factors into account. Their ultrahigh hydrothermal stability, large surface area, and especially the suitable pore diameter, as well as the high density of heteroatoms in the one-dimensional (1D) channel synergistically afford an intriguing performance in natural gas purification and recovery of C₂H₆ and C₃H₈. Adsorption isotherms for CH₄, C₂H₆, and C₃H₈ were determined by a volumetric method. The ideal adsorbed solution theory (IAST) selectivity of C₂H₆/CH₄, C₃H₈/CH₄, and C₃H₈/C₂H₆ at various ratios, as well as the isosteric heats of adsorption for all three gases were calculated. Ternary fixed-bed breakthrough experiments were carried out to further confirm their potential for real-world applications. Finally, density functional theory (DFT) calculation was applied to study the adsorption mechanism for CH₄, C₂H₆, and C₃H₈. 

All reagents were purchased commercially and used as received. Aluminum chloride hexahydrate (AlCl₃·6H₂O) was purchased from Alfa Aesar (USA); 3,5-pyrazoledicarboxylic acid monohydrate (H₃PDC) and 2,5-furandicarboxylic acid were both supplied by TCI America (USA); sodium hydroxide (NaOH) was purchased from Acros Organics (USA); the high-purity gases for adsorption experiments were obtained from Praxair, Inc. (USA). 

MOF-303 was prepared by using the procedure reported by Yaghi et al. [33] with some modifications. First, 1.04 g AlCl₃·6H₂O (4.308 mmol) and 0.75 g H₃PDC (4.308 mmol) were dissolved in 72 mL water in a 200 mL glass flask, 3 mL aqueous NaOH (0.26 g, 6.5 mmol) were added dropwise to the above mixture under stirring. The flask was then heated at 100 °C with reflux for 12 h. After cooling down to room temperature, the assynthesized MOF-303 powder was obtained by filtration. To remove the remaining 3,5-pyrazoledicarboxylic acid, the powder was washed thoroughly with water, followed by heated under vacuum at 150 °C for 12 h. MIL-160 was synthesized by the same procedure as that of MOF-303 by replacing the ligand H₃PDC with 2,5-furandicarboxylic acid.

Powder X-ray diffraction (PXRD) patterns were collected on a Bruker D8 Venture X-ray diffractometer (Bruker, USA) with a 2θ range of 3°–35° at 2.0(°)·min^–1 . Thermogravimetric (TG) measurements were performed on a TA Q-5000 apparatus (TA Instruments, USA), with a ramping rate of 10 K·min^–1 from ambient temperature to 973 K under a flowing nitrogen environment. Nitrogen (N₂) adsorption isotherms were obtained on a Micromeritics 3Flex analyzer (Micromeritics Instrument Corporation, USA) at 77 K. The Brunauer–Emmett–Teller (BET) model was chosen to evaluate the specific surface area, and the Horvath–Kawazoe (HK) method was conducted to acquire the micropore size distribution.

CH₄, C₂H₆, and C₃H₈ adsorption isotherms were performed on the 3Flex analyzer. Volumetric sorption data were collected at varied temperatures and pressures up to 1 bar. Approximately 80– 100 mg of sample were used and degassed at 423 K for 12 h prior to the adsorption experiments.

Breakthrough curves of a ternary mixture CH₄/C₂H₆/C₃H₈ (85:10:5, v/v/v) were obtained on a homemade experimental setup under the control of a mass flow meter, with the flow rate set to be 2 mL·min^–1 . A small adsorption column was prepared by packing about 0.2 g of activated sample into a long stainless hollow cylinder. The real time concentration of the effluent component was monitored by gas chromatography (Agilent, USA). Before the experiment, the packed column was heated at 423 K under He flow (5 mL·min^–1 ) for 1 h. After the breakthrough experiment, the desorption curves were collected at 323 K under 5 mL·min^–1 N₂ flow.

All ab initio calculations were performed using DFT in Vienna ab initio simulation package (VASP)[34,35], with van der Waals density functional (vdW-DF) method[36–39] to take into account of important van der Waals interactions. All the MOF unit cells were optimized by carrying out spin-polarized calculations, with self-consistent field (SCF) convergence of 0.1 meV (1 meV = 1.6 × 10^–22 J) and the plane wave energy cut-off set at 600 eV. The unit cell parameters and ions were allowed to move till the force acting between atoms reached below 5 meV·Å^–1 . Potential binding sites were studied by placing CH₄, C₂H₆, and C₃H₈ molecules in MOF-303 and MIL-160 at various sites and all the atoms were allowed to relax in accordance with the convergence condition. Difference in the total energies of the MOF unit cells and the guest molecules was used to calculate the corresponding binding energies. Induced charge densities were also calculated that maps the variation in charge density upon introduction of the guest molecules and help identifying the interactions happening at the binding sites. 

MOF-303 and MIL-160 are built from 1D infinite chain of [Al(OH)(COO)₂]_n linked through 3,5-pyrazoledicarboxylate and 2,5-furandicarboxylate, respectively, to form three-dimensional (3D) networks with straight 1D open channels, as shown in Fig. 2(a). Phase purity of the powder samples was confirmed by PXRD analysis (Fig. 2(b)). The PXRD patterns of as-synthesized samples match well with the corresponding simulated patterns. N₂ sorption experiments were conducted at 77 K to establish permanent microporosity of the samples. As shown in Figs. S1 and S2 (in Appendix A), the N₂ uptake of MOF-303 and MIL-160 increases sharply and reaches saturation at very low pressure with high adsorption capacities, indicating high microporosity of the two MOFs. MOF-303 and MIL-160 exhibit large BET surface area of 1220 and 1188 m² ·g^–1 , respectively, and uniform micropore with size of 5–7 Å (Fig. 2(c)), which are well-suited for adsorption of C₃H₈ and C₂H₆ at low concentrations. Thermogravimetric analysis (TGA) was carried out to investigate the thermal stability of the two MOFs. As shown in Fig. S3 in Appendix A, both MOF-303 and MIL-160 show two distinct weight loss steps: The first step before 125 °C corresponds to the physically adsorbed solvent molecules, and the second step following the plateau starting from 420 and 350 °C relates to structure decomposition, indicating their high thermal stability. 

Fig. 2. (a) Pore aperture and 1D channel of MOF-303 and MIL-160. Color scheme: red, grey, pink, and light blue balls represent O, C, Al, and N atoms, respectively. (b) Experimental and simulated PXRD patterns of MOF-303 and MIL-160. (c) Pore size distribution of MOF-303 and MIL-160.

The high stability, large surface area, and especially the suitable pore diameter, as well as the high density of N or O atoms decorating the 1D channels of the two MOFs prompted us to investigate their separation performance for natural gas purification/upgrading and recovering of C₃H₈ and C₂H₆ from the gas mixture. Single-component adsorption isotherms of CH₄, C₂H₆, and C₃H₈ for MOF-303 and MIL-160 were collected at 298 K (Figs. 3(a) and (b)). Both C₃H₈ isotherms of MOF-303 and MIL-160 exhibit type I adsorption profile with very steep slopes at low pressure and reach saturation below 20 kPa, indicating strong interaction between C₃H₈ molecule and the frameworks. Notably, at 298 K and 1 bar,  MOF-303 and MIL-160 adsorb 4.74 and 5.08 mmol·g^–1 of C₃H₈, respectively. At a low pressure of 5 kPa relevant to the typical partial pressure of C3H8 in nature gas, the corresponding uptakes remain as high as 3.38 and 2.48 mmol·g^–1 , much higher than those of many reported MOFs, such as University of Texas at San Antonio (UTSA)-35a [40], Fujian Institute of Research (FIR)-7a-ht [41], and MIL-100(Fe) [16], but lower than Mg/Fe/Co-MOF-74 (about 4.1 mmol·g^–1 ) [17], 0.3Gly@HKUST-1 (4.22 mmol·g^–1 ), and crystalline porous material (CPM)-734c (about 3.7 mmol·g^–1 ) [42]. This indicates the potential of MOF-303 and MIL-160 for the recovery of low pressure C₃H₈ from CH₄ stream. As shown in Figs. 3(a) and (b), the adsorption isotherms of C₂H₆ can also be characterized as type I but with much smaller slope compared to those of C₃H₈, which may be ascribed to the weaker interaction between C₂H₆ molecule and the frameworks. The C₂H₆ uptakes are as high as 4.96 and 4.65 mmol·g^–1 at 298 K and 1 bar for MOF-303 and MIL-160, respectively. At a relatively low pressure (10 kPa) the values are 1.59 and 1.55 mmol·g^–1 , respectively, outperforming many reported MOFs, such as Zn-SDBA (H₂SDBA: 4,4' -sulfonyldibenzoic acid) [43], MIL-142A [44], and porous coordination network (PCN)-224 [45], except Mg/Fe/Co-MOF-74 (about 3.2 mmol·g^–1 ) [17,46], Co2V-bdc-tpt (bdc: terephthalate; tpt: 2,4,6- tri(4-pyridyl)-1,3,5-triazine; about 2.3 mmol·g^–1 ) [47], and Ni(TMBDC)(DABCO)_0.5 (about 2.93 mmol·g^–1 ) [23]. This further confirms that the two MOFs are promising candidates for simultaneous capture of C₃H₈ and C₂H₆ from nature gas. As for CH₄, on the contrary, the isotherms are nearly straight lines with relatively low equilibrium uptake capacities of 0.86 and 0.94 mmol·g^–1 for MOF-303 and MIL-160, respectively, suggesting weak affinity of the frameworks toward the CH₄ molecules. 

Fig. 3. Adsorption (Ads)–desorption (Des) isotherms of C₃H₈, C₂H₆, and CH₄ on (a) MOF-303 and (b) MIL-160 at 298 K. (c) IAST selectivities of MOF-303 and MIL-160 for C₃H₈/ CH₄ (5:85, v/v) and C₂H₆/CH₄ (10:85, v/v) at 298 K. (d) Comparison of IAST selectivities and adsorbed amounts of C₃H₈ at 298 K and 5 kPa on MOF-303, MIL-160, and previously reported top-performing MOFs (JLU: Jilin University; MFM: Manchester framework material; H₂SDBA: 4,4' -sulfonyldibenzoic acid).

To quantify the extent of interactions between the frameworks and the three hydrocarbons, isosteric heats of adsorption (Q_st) for CH₄, C₂H₆, and C₃H₈ were calculated (Figs. S6 and S7 in Appendix A). The zero coverage Q_st for MOF-303 follows the following sequence: C₃H₈ (34 kJ·mol^–1 )>C₂H₆ (24 kJ·mol^–1 ) > CH₄ (19 kJ·mol^–1 ), which is consistent with the order of the adsorbed amounts. Similarly, for MIL-160, the Q_st values follow the same order: C₃H₈ (35 kJ·mol^–1 )>C₂H₆ (28 kJ·mol^–1 ) > CH₄ (19 kJ·mol^–1 ). The apparent differences for the three gas species may result from their different polarizability and molecule size. For C₃H₈, having the highest polarizability (6.3 × 10^–24 cm³ ) among the three and the largest molecule dimension that is close to the pore size of the two MOFs guarantee that appreciably strong hydrogen bonds could be formed with the frameworks upon its adsorption. In contrast, CH₄ possesses a relatively low polarizability (2.6 × 10^–24 cm³ ) and a much smaller molecule size, leading to insufficient contacts with the pore surface and a much weaker interaction. The distinct differences in Q_st and adsorption capacity for CH₄, C₂H₆, and C₃H₈ make MOF-303 and MIL-160 excellent adsorbents for recovering C₃H₈ and C₂H₆ from natural gas. To more precisely evaluate the separation performance of the two MOFs under mixed-gas conditions, we calculated IAST selectivities of C₃H₈/CH₄ (5:85, v/v) and C₂H₆/CH₄ (10:85, v/v) at room temperature (298 K). As shown in Fig. 3(c), for MOF-303, the selectivity of C₃H₈/CH₄ (5:85, v/v) at 100 kPa reaches 5114, which, to the best of our knowledge, has set a new record. In addition, the selectivity for C₂H₆/CH₄ (10:85, v/v) is as high as 26, surpassing many reported MOFs (Fig. S7). Compared to MOF-303, MIL-160 possesses a similar C₂H₆/CH₄ (10:85, v/v) selectivity (20) but a much lower C₃H₈/CH₄ (5:85,  v/v) selectivity (174), mainly attributed to the lower C₃H₈ uptake amount at low pressure and the slightly larger adsorbed amount of CH₄. 

As a comparation, the uptake capacities of C₃H₈ and C₂H₆ combined with the C₃H₈/CH₄ and C₂H₆/CH₄ selectivities for MOF-303, MIL-160, and some representative MOFs are listed in Fig. 3(d) and Fig. S8 (in Appendix A). The C₃H₈/CH₄ selectivity of MOF303 (5114) is the highest value reported by far and notably higher than those of top-performing MOFs, including Ni(TMBDC)- (DABCO)_0.5, BSF-2, and MIL-142A. Additionally, the C₃H₈ uptake amount (3.38 mmol·g^–1 ) is comparable to Ni(TMBDC)(DABCO)_0.5 (3.37 mmol·g^–1 ) and exceeds other MOFs, such as UTSA-35a, Manchester framework material (MFM)-202a [48], Zr-SDBA [49], and MIL-142A. For C₂H₆/CH₄, as shown in Fig. S7, MOF-303 also outperforms most of the other MOFs with higher selectivity (26) and uptake capacity (1.59 mmol·g^–1 ), such as BSF-2, ZnSDB, and UTSA-35a, but lower than that of Ni(TMBDC)(DABCO)_0.5 and Mg/Co/Fe-MOF-74[17,46]. The ultrahigh selectivity combined with the large adsorption amount of C₃H₈ and C₂H₆ at both 100 kPa and low pressure (5 or 10 kPa) suggests that MOF-303 is of great promise for use as adsorbent in natural gas upgrading. Both the uptake amounts and selectivities of MIL-160 are slightly lower than those of MOF-303, which may be attributed to the larger pore size and the lower density of heteroatoms in MIL-160. Regardless, MIL-160 still features higher uptake and selectivity than the majority of the MOFs listed. It should be noted that while it seems MgMOF-74 and Ni(TMBDC)(DABCO)_0.5 are more promising for C₂H₆ recovery (Fig. S8) in terms of adsorption capacity and selectivity, the former suffer from low moisture resistance, and the latter is composed of an expensive ligand (TMBDC). In contrast, both MOF-303 and MIL-160 feature high thermal and moisture stability. To further confirm their outstanding hydrothermal stability, PXRD patterns of samples were collected after being treated under different conditions, including exposure to moisture for one month. As presented in Figs. S9–S12 (in Appendix A), compared to the results of as-synthesized samples, there are no notable differences found in the PXRD patterns of the samples after various treatments, confirming the excellent hydrothermal stability of both materials. As for the cost, the ligands of MOF-303 and MIL-160 are both inexpensive, and the MOFs could be readily synthesized under mild conditions. Furthermore, to assess the scale-up capability, we synthesized the two MOF sample in 5 g scale. Highquality powder products were obtained by constant stirring the mixture of ligands, aluminum salts, water, and NaOH in a glass flask at 100 °C for 12 h, with the yield higher than 90% (Figs. S13–S18 in Appendix A). The high moisture stability, low cost, and the facile scale-up capability further corroborate the feasibility for the implementation of MOF-303 and MIL-160 in industrial separation technology. 

To understand the gas adsorption behavior and mechanism in MOF-303 and MIL-160, DFT calculations were performed on both structures. As shown in Figs. 4(a)–(c), all three guest molecules at their primary binding positions occupy similar sites in the pore of MOF-303. The binding energy calculations show a binding strength order of C₃H₈ (60.1 kJ·mol^–1 )>C₂H₆ (47.4 kJ·mol^–1 ) > CH₄ (30.7 kJ·mol^–1 ) at their primary binding sites located near the MOF linker. This result agrees with the experimental uptake trends for MOF-303 at low pressures. The induced charge density for the three gas molecules (Figs. 4(d)–(f)) shows most charge rearrangement occurring between the guest molecules and the N atoms in the linker, confirming that the N atoms are the strongest binding sites in MOF-303. As shown in Figs. 4(c) and (f), the highest binding energy and induced charge density for C₃H₈ are likely a result of its longer C3 chain, larger kinetic diameter, and a greater number of C–H arms as compared with C₂H₆ and CH₄, which enable it to interact more closely with multiple linkers and form multiple stronger hydrogen bonds. The charge rearrangements for MIL-160 are shown in Fig. S19 (in Appendix A). All three guest molecules prefer binding near the linkers and interact primarily with the O atoms on both the furan ring and the carboxyl groups via their C–H bonds. Different from their binding sites in MOF-303, CH₄ and C₂H₆ molecules bind close to linkers on one side of pore (Figs. S19(d) and (e)), which may be attributed to the larger pore size of MIL-160 (Fig. 2(c)). On the other hand, C₃H₈, owing to its larger size, occupies a more central position in the pore and interacts with linkers on three different sides. The binding energy calculations for MIL-160 generate the same trend as that of MOF-303, with the descending order of C₃H₈ (65.7 kJ·mol^–1 )>C₂H₆ (55.8 kJ·mol^–1 ) > CH₄ (34.9 kJ·mol^–1 ) at the primary binding site (Figs. S19(a)–(c)), in consistent with the experimental observations. 

Fig. 4. The unit cell of MOF-303 used for calculating binding energies. (a–c) The results for (a) CH₄, (b) C₂H₆, and (c) C₃H₈ show their primary binding site (color scheme: silver, red, black, blue, and white balls represent Al, O, C, N, and H). (d–f) Induced charge densities for (d) CH₄, (e) C₂H₆, and (f) C₃H₈ (iso-level is 0.001 electrons·Å^–3 ). Blue highlighted areas represent a depletion of charge and yellow areas represent an increase in charge after the guest molecule occupies a binding site.

To further evaluate the actual separation potential of MOF-303 and MIL-160, dynamic breakthrough experiments were carried out on ternary (CH₄/C₂H₆/C₃H₈, 85:10:5, v/v/v) gas mixtures at 298 K. For the breakthrough curves of MOF-303, as shown in Fig. 5(a), CH₄ eluted out first at 15 min·g^–1 , followed by C₂H₆ and C₃H₈ with a breakthrough time of 120 and 760 min·g^–1 , respectively, coinciding well with the order of static capacities and isosteric heats. The distinct breakthrough times for the three gases confirm that MOF303 can afford efficient natural gas upgrading by the individual C₃H₈ and C₂H₆ recovery (as shown in Fig. S20 in Appendix A). The breakthrough curves of MIL-160 are similar to those of MOF303 but exhibit a much shorter breakthrough time for C₃H₈ (388 min·g^–1 ), as shown in Fig. 5(b), which is consistent with the lower static adsorption capacity of MIL-160 for C₃H₈ at 5 kPa. To evaluate the regeneration property of MOF-303 and MIL-160, desorption was carried out under dynamic N₂ flowing at 333 K. As shown in Fig. 5(c), during the desorption process for MOF-303, CH₄, C₂H₆, and C₃H₈ can be fully removed in 4, 12, and 50 min, respectively, demonstrating that MOF-303 column can be fully regenerated under mild condition. Finally, five breakthrough measurements were carried out consecutively to evaluate the recycling performance of MOF-303 and MIL-160. As illustrated in Fig. 5(d) and Fig. S21 (in Appendix A), the breakthrough times for C₃H₈ and C₂H₆ are nearly constant, suggesting good recyclability of both adsorbents. 

Fig. 5. (a, b) Ternary breakthrough curves (CH₄/C₂H₆/C₃H₈, 85:10:5, v/v/v) of (a) MOF-303 and (b) MIL-160 at 298 K. (c) Desorption curves of MOF-303 packed column at 333 K under 5 mL·min^–1 N₂ flow. (d) C₃H₈ and C₂H₆ breakthrough times of MOF-303 in consecutive five cycles of breakthrough experiments (298 K and 100 kPa).

In summary, two highly stable Al-based MOFs, MOF-303 and MIL-160, have been investigated for efficient separation and recovery of C₂H₆ and C₃H₈ from natural gas. The large surface area, suitable pore diameter, and the high density of N or O atoms in the 1D open channels synergistically enhance the affinity of the frameworks toward C₃H₈ and C₂H₆, resulting in large uptake capacity and excellent selectivity. In particular, for MOF-303, the uptake of C₃H₈ at 298 K and 5 kPa is up to 3.38 mmol·g^–1 along with a record-high IAST selectivity of 5114 for C₃H₈/CH₄ (5:85, v/v). MOF-303 also possesses high adsorption capacity for C₂H₆ (at 10 kPa) and high C₂H₆/CH₄ (10:85, v/v) selectivity, reaching values of 1.59 mmol·g^–1 and 26, respectively. DFT calculations verified that the strong affinity between C₃H₈ (or C₂H₆) molecules and the heteroatoms on the linkers gives rise to the high loading capacity and selectivity for C₃H₈ and C₂H₆. To investigate the potential of using MOF-303 and MIL-160 to upgrade natural gas and to recover C₃H₈ and C₂H₆, further experiments, including hydrothermal stability and scale-up capability tests, as well as breakthrough experiments, were carried out on both MOFs. The stability tests revealed their exceptional resistance to moisture. The scale-up capabilities were verified through reactions at 5 g scale with quantitative yields. Finally, ternary breakthrough experiments and recyclability tests further confirmed the great potential of MOF-303 and MIL160 as advanced adsorbents for efficient separation of C₃H₈/C₂H₆/ CH₄. 

cknowledgment We would like to thank the US Department of Energy, Office of Science, Office of Basic Energy Sciences (DE-SC0019902) for the partial support of this work. Shikai Xian, Junjie Peng, and Hao Wang acknowledge the financial support from National Natural Science Foundation of China (21908069 and 21901166), Guangdong Natural Science Foundation (2019A1515010692), and Shenzhen Science and Technology Program (JCYJ20190809145615620 and RCYX20200714114539243).

Shikai Xian, Junjie Peng, Haardik Pandey, Timo Thonhauser, Hao Wang, and Jing Li declare that they have no conflict of interest or financial conflicts to disclose.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.eng.2022.07.017.