The confinement effect of porous materials on the thermodynamical equilibrium of the CO₂ hydrogenation reaction presents a cost-effective alternative to transition metal catalysts. In metal-organic frameworks, the type of metal center has a greater impact on the enhancement of formic acid production than the scale of confinement resulting from the pore size. The M-MOF-74 series enables a comprehensive study of how different metal centers affect HCOOH production, minimizing the effect of pore size. In this work, molecular simulations were used to analyze the adsorption of HCOOH and the CO₂ hydrogenation reaction in M-MOF-74, where M = Ni, Cu, Co, Fe, Mn, Zn. We combine classical simulations and density functional theory calculations to gain insights into the mechanisms that govern the low coverage adsorption of HCOOH in the surrounding of the metal centers of M-MOF-74. The impact of metal centers on the HCOOH yield was assessed by Monte Carlo simulations in the grand-canonical ensemble, using gas-phase compositions of CO₂, H₂, and HCOOH at chemical equilibrium at 298.15-800 K, 1-60 bar. The performance of M-MOF-74 in HCOOH production follows the same order as the uptake and the heat of HCOOH adsorption: Ni > Co > Fe > Mn > Zn > Cu. Ni-MOF-74 increases the mole fraction of HCOOH by ca. 10⁵ times compared to the gas phase at 298.15 K, 60 bar. Ni-MOF-74 has the potential to be more economically attractive for CO₂ conversion than transition metal catalysts, achieving HCOOH production at concentrations comparable to the highest formate levels reported for transition metal catalysts and offering a more valuable molecular form of the product.

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The series of metal–organic frameworks M-MOF-74 gained popularity in the field of capture and separation of CO₂ due to the presence of numerous, highly reactive open-metal sites. The description of effective interactions between guest molecules and open-metal sites without accounting for polarization effects is challenging but it can significantly reduce the computational cost of simulations. In this study, we propose a non-polarizable force field for CO₂, and H₂ adsorption in M-MOF-74 (M = Ni, Cu, Co, Fe, Mn, Zn) by scaling the Coulombic interactions of M-MOF-74 atoms, and Lennard-Jones interaction potentials between the center of mass of H₂ and the open-metal centers. The presented force field is based on UFF and DREIDING parameters, characterized by high transferability and efficiency. The quantum behavior of H₂ at cryogenic temperatures is considered by incorporating Feynman–Hibbs quantum corrections. To validate the force field, the experimental isotherms of CO₂ at 298 K and 10⁻¹ – 10²kPa, the isotherms of H₂ at 77 K and 10⁻⁵ – 10²kPa, the corresponding enthalpy of adsorption, and the binding geometries in the M-MOF-74 series were reproduced using Monte Carlo simulations in the grand-canonical ensemble. The computed loadings, heats of CO₂ and H₂ adsorption, and binding geometries in M-MOF-74 are in very good agreement with the experimental values. The temperature transferability of the force field from 77 K to 87 K, and 298 K was shown for adsorption of H₂. The validated force field was used to study the adsorption and separation of CO₂/H₂ mixtures at 298 K. The adsorption of H₂ practically does not occur when CO₂ is present in the mixture. As indicated from simulated breakthrough curves, the breakthrough time of CO₂ in M-MOF-74 follows the same order as the uptake and the heat of CO₂ adsorption: Ni ¿ Co ¿ Fe ¿ Mn ¿ Zn ¿ Cu. Increasing the feed mole fraction of CO₂ in the breakthrough simulations from 0.1 to 0.9 speeds up the saturation of the adsorbent, leading to a faster exit of CO₂ with the column effluent. The application of the non-polarizable force field allows full investigation of the capture and separation of CO₂ in M-MOF-74, and can be expanded to study multi-component mixtures or industrial reactions in future research.

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In a world where capture and separation processes represent above 10% of global energy consumption, novel porous materials, such as Metal-Organic Frameworks (MOFs) used in adsorption-based processes are a promising alternative to dethrone the high-energy-demanding distillation. Shape and size tailor-made pores in combination with Lewis acidic sites can enhance the adsorbate-adsorbent interactions. Understanding the underlying mechanisms of adsorption is essential to designing and optimizing capture and separation processes. Herein, we analyze the adsorption behaviour of light hydrocarbons (methane, ethane, ethylene, propane, and propylene) in two synthesized copper-based MOFs, Cu-MOF-74 and URJC-1. The experimental and computational adsorption curves reveal a limited effect of the exposed metal centers on the olefins. The lower interaction Cu-olefin is also reflected in the calculated enthalpy of adsorption and binding geometries. Moreover, the diamond-shaped pores' deformation upon external stimuli is first reported in URJC-1. This phenomenon is highlighted as the key to understanding the adsorbent's responsive mechanisms and potential in future industrial applications.

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According to the European Commission, in 2016 the residential sector represented 25.4% of the final energy consumption. Heating and cooling in EU households account for 69.1% of the total energy consumption. The fraction of 84% for heating and cooling is still generated from fossil fuels, and only 16% is generated from renewable energy. To decrease carbon dioxide emissions of fossil fuel consumption, it is crucial to find alternatives to supply the heating and cooling demand. Alternatives such as adsorption-based heat pumps and desiccant cooling systems are receiving much attention because of their moderate energy consumption. These systems are based on the energetic exchange during the adsorption/desorption of working fluids. In this work, we combined experiments and simulations to evaluate the viability of several zeolites and MOFs with water for cooling systems applications. We combined the study of adsorption mechanisms and the dynamics of water inside the pores of the structures, thereby obtaining an overall understanding of the working pair. We found that the Al content in FAU-topology zeolites is a key factor for an efficient process. We also identify ZJNU-30 metal–organic framework as a suitable candidate for cooling applications because of its outstanding water capacity, cooling capacity, and coefficient of performance.@en

The separation and purification of light hydrocarbons is challenging in the industry. Recently, a ZJNU-30 metal-organic framework (MOF) has been found to have the potential for adsorption-based separation of olefins and diolefins with four carbon atoms [H. M. Liu et al. Chem. - Eur. J. 2016, 22, 14988-14997]. Our study corroborates this finding but reveals Fe-MOF-74 as a more efficient candidate for the separation because of the open metal sites. We performed adsorption-based separation, transient breakthrough curves, and density functional theory calculations. This combination of techniques provides an extensive understanding of the studied system. Using this MOF, we propose a separation scheme to obtain a high-purity product.

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The separation of light olefins from paraffins via cryogenic distillation is a very energy intensive process. Solid adsorbents and especially metal-organic frameworks with open metal sites have the potential to significantly lower the required energy. Specifically, M-MOF-74 has drawn considerable attention for application in olefin/paraffin separation. To investigate how the separation proceeds on a molecular level and to design better materials, molecular simulation can be a useful tool. Unfortunately, it is still a challenge to model the adsorption behavior of many adsorbates in metal-organic frameworks with open metal sites. Previously, the inclusion of explicit polarization has been suggested to improve the quality of classical force fields for such systems. Here, the potential of polarizable force fields for the description of olefins and paraffins in metal-organic frameworks with open metal sites is investigated. In particular, heats of adsorption, binding geometries, and adsorption isotherms are calculated for C2H4, C2H6, C3H6, and C3H8 in M-MOF-74 (with M = Co, Mn, Fe, and Ni). In this study, no force field parameters are adjusted to improve the model. The results show that including explicit polarization significantly improves the description of the adsorption in comparison to non-polarizable generic force fields which do not consider explicit polarization. The study also reveals that simulation predictions are sensitive to the assigned repulsive potential and framework charges. A fully re-parametrized polarizable force field may have the capability to improve the predictions even further.

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An increase in demand for energy efficient processes for the separation of saturated and unsaturated light hydrocarbons mixtures drives the need of noncryogenic processes. The adsorptive separation using Metal-Organic Frameworks with coordinatively unsaturated metal sites may provide a cost-effective alternative due to the strong binding of the metal cation with the unsaturated hydrocarbons. Since experiments on adsorption equilibrium of gas mixtures are challenging, we propose classical force field based simulations to analyse the ability of MOF-74 with different metal substitutions for the separation of C2 and C3 olefin/paraffin binary mixtures. We parametrized the force field by fitting to available experimental single-component adsorption isotherms of ethane, ethene, propane, and propene in M–MOF-74 (M=Co, Fe, Mn, and Ni). The force field was validated for a variety of temperatures ranged from 273 K to 353 K. We then conducted Monte Carlo simulations in the Grand-Canonical ensemble to elucidate the adsorption mechanisms of the saturated/unsaturated hydrocarbon mixtures, at 318 K and 353 K. We computed the adsorption isotherms, and from these the adsorption selectivity, and addressed the variations of MOF properties with different metal cations. Fe-based MOF-74 appears the best option for both ethane/ethene and propane/propene separation applications. This finding partly agrees with previous work based on the Ideal Adsorbed Solution Theory.@en