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The realization of porous materials for highly selective separation of acetylene (C2H2) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann‐type metal−organic framework (MOF), Co(pyz)[Ni(CN)4] (termed as ZJU‐74a), that features sandwich‐like binding sites for benchmark C2H2 capture and separation is reported. Gas sorption isotherms reveal that ZJU‐74a exhibits by far the record C2H2 capture capacity (49 cm3 g−1 at 0.01 bar and 296 K) and thus ultrahigh selectivity for C2H2/CO2 (36.5), C2H2/C2H4 (24.2), and C2H2/CH4 (1312.9) separation at ambient conditions, respectively, of which the C2H2/CO2 selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU‐74a can construct a sandwich‐type adsorption site to offer dually strong and cooperative interactions for the C2H2 molecule, thus leading to its ultrahigh C2H2 capture capacity and selectivities. The exceptional separation performance of ZJU‐74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C2H2/CO2, 1/99 C2H2/C2H4, and 50/50 C2H2/CH4 mixtures under ambient conditions.

We present a method to determine potential parameters in molecular simulations of confined systems through fitting on experimental isotherms with inflection points. The procedure uniquely determines the adsorbent-adsorbate interaction parameters and is very sensitive to the size parameter. The inflection points in the isotherms are often related to a subtle interplay between different adsorption sites. If a force field can predict this interplay, it also reproduces the remaining part of the isotherm correctly, i.e., the Henry coefficients and saturation loadings. DOI: 10.1103/PhysRevLett.93.088302 PACS numbers: 82.75.Jn, 47.55.Mh, 66.30.-h The effect of confinement on adsorption and diffusion is still poorly understood despite its importance for practical applications. The performance of molecular sieves in separation and catalytic processes depends critically on the match between sieve topology and the shape and size of the adsorbate [1]. It is therefore of considerable industrial importance to explore the adsorption and diffusion of linear and branched alkanes in different topologies using realistic simulations at the microscopic level [2]. Different parameter sets yield values of diffusivities that differ not only quantitatively but also show a different qualitative dependence on the molecular loading [3]. The critical unresolved question follows: Which of these parameter sets is the most physically realistic one? Here, we hope to remedy this situation.Potential parameter sets can be checked only via comparison with experiment. For diffusion the comparison is complicated by large discrepancies between microscopic and macroscopic experimental measurement methods, and even within the same measurement technique there are many disagreements between various studies. However, adsorption results seem to be well established and provide a more solid basis for a detailed comparison between experiment and simulation. Moreover, a large amount of data exists on adsorption of hydrocarbons in siliceous zeolites.Silicalite-1 (Fig. 1) consists of a three-dimensional pore system with straight parallel channels, intersected by zigzag channels [4]. The channels of approximately 6 Å in diameter lead to shape selectivity, especially for the isomers of hexane, which have dimensions close to the silicalite-1 pores. The linear channels intersect with the zigzag channels 4 times per unit cell. Interestingly, for n-heptane and for the branched alkanes in silicalite-1 a kink in the isotherm is observed [5]. This inflection is directly related to the number of intersections in the structure and occurs at exactly four molecules per unit cell. As these inflections are caused by a subtle interplay between the size and configuration of the molecule and two different adsorption sites, it becomes clear that the adsorbent-adsorbate potential size parameter is the most sensitive parameter in the force field.In general, adsorption in any periodic structure has steps or kinks. The reason is that steps and kinks signal transitions between diffe...

Separation of C 2 H 4 from C 2 H 4 /C 2 H 2 /C 2 H 6 mixture with high working capacity is still a challenging task. Herein, we deliberately design a Th-metal-organic framework (MOF) for highly efficient separation of C 2 H 4 from a binary C 2 H 6 /C 2 H 4 and ternary C 2 H 4 /C 2 H 2 /C 2 H 6 mixture. The synthesized MOF Azole-Th-1 shows a UiO-66-type structure with fcu topology built on a Th 6 secondary building unit and a tetrazole-based linker. Such noticeable structure, is connected by a N,O-donor ligand with high chemical stability. At 100 kPa and 298 K Azole-Th-1 performs excellent separation of C 2 H 4 (purity > 99.9%) from not only a binary C 2 H 6 / C 2 H 4 (1:9, v/v) mixture but also a ternary mixture of C 2 H 6 /C 2 H 2 /C 2 H 4 (9:1:90, v/v/v), and the corresponding working capacity can reach up to 1.13 and 1.34 mmol g −1 , respectively. The separation mechanism, as unveiled by the density functional theory calculation, is due to a stronger van der Waals interaction between ethane and the MOF skeleton.

In comparison with the fast development of binary mixture separations, ternary mixture separations are significantly more difficult and have rarely been realized by a single material. Herein, a new strategy of tuning the gate‐opening pressure of flexible MOFs is developed to tackle such a challenge. As demonstrated by a flexible framework NTU‐65, the gate‐opening pressure of ethylene (C2H4), acetylene (C2H2), and carbon dioxide (CO2) can be regulated by temperature. Therefore, efficient sieving separation of this ternary mixture was realized. Under optimized temperature, NTU‐65 adsorbed a large amount of C2H2 and CO2 through gate‐opening and only negligible amount of C2H4. Breakthrough experiments demonstrated that this material can simultaneously capture C2H2 and CO2, yielding polymer‐grade (>99.99 %) C2H4 from single breakthrough separation.

Molecular dynamics (MD) simulations have been carried out for pure components, binary, ternary, and quaternary mixtures containing methane, ethane, propane, and n-butane in FAU zeolite at 300 K for a range of molecular loadings Theta, approaching saturation limits. The n-dimensional matrix of Maxwell-Stefan (M-S) diffusivities [Delta], defined by (N) = -rho[Delta][Gamma](nabla Theta), was determined along with the self-diffusivities, D(i)(,self). Additionally, configurational-bias Monte Carlo (CBMC) simulations were carried out to obtain the pure component sorption isotherms and the saturation capacities Theta(i)(,sat). From the information on Delta(ij), D(i)(,self), and Theta(i)(,sat), the various M-S diffusivities were determined: (1) component D(i), reflecting the interactions of the species i with the zeolite, self-exchange D(ii), and (2) binary exchange D(ij). The obtained data underline the major advantage of the M-S formulation that at a given occupancy, theta = Sigma(N)(n)(i=l)Theta(j)/Theta(j)(,sat) within the zeolite, the D(i) has nearly the same value for species i whether this species is present on its own or in a mixture with other species. The same advantage holds, too, for the self-exchange D(ii); the value at a given occupancy, theta, is the same whether determined from pure component, binary, or ternary mixture data. For all binary and ternary mixtures studied, it was verified that the binary exchange coefficient D(ij) can be interpolated from the corresponding values of the self-exchange parameters D(ii) and D(jj) using a generalization of the interpolation formula developed earlier (Skoulidas et al., Langmuir, 2003, 19, 7977). We also demonstrate that if the occupancy dependence of the pure component parameters D(i) and D(ii) are modeled properly, this information is sufficient to provide very good estimates of the matrix [Delta] for mixtures with 2, 3, or 4 components over the entire range of loadings. Simulations of mixture diffusion of alkanes in MFI and LTA confirm that the above-mentioned advantages of the M-S formulation also hold for these zeolite topologies.

The separation of C2H2/CO2 is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)4] (FeNi‐M′MOF, pyz=pyrazine), with multiple functional sites and compact one‐dimensional channels of about 4.0 Å for C2H2/CO2 separation. This MOF shows not only a remarkable volumetric C2H2 uptake of 133 cm3 cm−3, but also an excellent C2H2/CO2 selectivity of 24 under ambient conditions, resulting in the second highest C2H2‐capture amount of 4.54 mol L−1, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C2H2 molecules and the binding sites of FeNi‐M′MOF. This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi‐M′MOF as a promising material for C2H2/CO2 separation.

Fort he separation of ethane from ethylene,i t remains challenging to target both high C 2 H 6 adsorption and selectivity in aC 2 H 6 -selective material. Herein, we report ar eversible solid-state transformation in al abile hydrogenbonded organic framework to generate an ew rod-packing desolvated framework (ZJU-HOF-1) with suitable cavity spaces and functional surfaces to optimally interact with C 2 H 6 .Z JU-HOF-1 thus exhibits simultaneously high C 2 H 6 uptake (88 cm 3 g À1 at 0.5 bar and 298 K) and C 2 H 6 /C 2 H 4 selectivity (2.25), which are significantly higher than those of most top-performing materials.T heoretical calculations revealed that the cage-like cavities and functional sites synergistically "match" better with C 2 H 6 to provides tronger multipoint interactions with C 2 H 6 than C 2 H 4 .Incombination with its high stability and ultralow water uptake,this material can efficiently capture C 2 H 6 from 50/50 C 2 H 6 /C 2 H 4 mixtures in ambient conditions under 60 %RH, providing arecordpolymer-grade C 2 H 4 productivity of 0.98 mmol g À1 .