Sandrine Bourrelly

High Uptakes of CO2 and CH4 in Mesoporous Metal—Organic Frameworks MIL-100 and MIL-101

Mesoporous MOFs MIL-100 and MIL-101 adsorb huge amounts of CO2 and CH4. Characterization was performed using both manometry and gravimetry in different laboratories for isotherms coupled with microcalorimetry and FTIR to specify the gas-solid interactions. In particular, the uptake of carbon dioxide in MIL-101 has been shown to occur with a record capacity of 40 mmol g(-1) or 390 cm3STP cm(-3) at 5 MPa and 303 K.

Hydrocarbon Adsorption in the Flexible Metal Organic Frameworks MIL-53(Al, Cr)

A general study of the adsorption of n-alkanes in the flexible metal organic framework (MOF) MIL-53 is presented. The roles of the length of the alkyl chain (n = 1-9), the nature of the metal (Al, Cr), and temperature were investigated. The shape of the adsorption curves is driven by the alkyl chain length of the n-alkanes. While traditional type-I isotherms are observed for short alkanes (n = 1, 2), adsorbates with longer chains induce clear substeps in the isotherm curves whose positions depend on the chain length. Such substeps are due to a breathing phenomenon, as proven by ex situ X-ray diffraction analysis. They strongly depend on the amount of adsorbate in the pores and on the nature of the metal (Al, Cr), which, for a given alkane, leads to a strong change in the substep positions despite the similar characteristics of the two metals. The adsorption kinetics are highly sensitive to small variations in temperature. Their detailed analysis in different regions of the isotherms shows in some cases the existence of distinct diffusion regimes and/or conformations within the flexible phases.

Complex Adsorption of Short Linear Alkanes in the Flexible Metal-Organic-Framework MIL-53(Fe)

This investigation is based on a combination of experimental tools completed by a computational approach to deeply characterize the unusual adsorption behavior of the flexible MIL-53(Fe) in the presence of short linear alkanes. In contrast to the aluminum or chromium analogues we previously reported, the iron MIL-53 solid, which initially exhibits a closed structure in the dry state, shows more complex adsorption isotherms with multisteps occurring at pressures that depend on the nature of the alkane. This behavior has been attributed to the existence of four discrete pore openings during the whole adsorption process. Molecular simulations coupled with in situ X-ray powder diffraction were able to uncover these various structural states.

Explanation of the Adsorption of Polar Vapors in the Highly Flexible Metal Organic Framework MIL-53(Cr)

A comparison of the adsorption of water, methanol, and ethanol polar vapors by the flexible porous chromium(III) terephthalate MIL-53(Cr) was investigated by complementary techniques including adsorption gravimetry, ex situ X-ray powder diffraction, microcalorimetry, thermal analysis, IR spectroscopy, and molecular modeling. The breathing steps observed during adsorption strongly depend on the nature of the vapor. With water, a significant contraction of the framework is observed. For the alcohols, the initial contraction is followed by an expansion of the framework. A combination of IR analysis, X-ray diffraction, and computer modeling leads to the molecular localization of the guest molecules and to the identification of the specific guest-guest and host-guest interactions. The enthalpies of adsorption, measured by microcalorimetry, show that the strength of the interactions decreases from ethanol to water. Differential scanning calorimetry experiments on an EtOH/H(2)O mixture suggest a selective adsorption of ethanol over water.

Energy-Efficient Dehumidification over Hierachically Porous Metal–Organic Frameworks as Advanced Water Adsorbents

Water sorption technologies are widely used commercially in many contexts, including industrial or indoor desiccant applications such as desiccant dehumidifiers, gas dryers, adsorptive air conditioning systems, fresh water production, adsorption heat transformation, etc.[1] In recent years, the potential for energy savings through improved efficiency has received increased attention, particularly as low-grade thermal energy or solar energy could be utilized. Currently, silica gel and zeolites are widely utilized commercially, often formed into corrugated honeycomb rotors.[1] As these sorbents typically must be heated above 150 °C during the desorption step, these sorbents are far from ideal in terms of energy consumption. There are additional issues with the level of dehumidification that these materials are able to achieve.[1] Improved energy efficiency requires advanced water adsorbents that can be regenerated together with the removal of a large amount of water vapor from humid conditions.[1] If such materials could operate at or below 80 °C, they could utilize readily available waste heat, leading to further energy savings. Among the existing classes of porous solids, crystalline metal–organic frameworks (MOFs)[2] are currently of great

An evaluation of UiO-66 for gas-based applications.

In addition to its high thermal stability, repetitive hydration/dehydration tests have revealed that the porous zirconium terephthalate UiO-66 switches reversibly between its dehydroxylated and hydroxylated versions. The structure of its dehydroxylated form has thus been elucidated by coupling molecular simulations and X-ray powder diffraction data. Infrared measurements have shown that relatively weak acid sites are available while microcalorimetry combined with Monte Carlo simulations emphasize moderate interactions between the UiO-66 surface and a wide range of guest molecules including CH(4), CO, and CO(2). These properties, in conjunction with its significant adsorption capacity, make UiO-66 of interest for its further evaluation for CO(2) recovery in industrial applications. This global approach suggests a strategy for the evaluation of metal-organic frameworks for gas-based applications.

Effect of the organic functionalization of flexible MOFs on the adsorption of CO2

The adsorption of CO2 by a series of functionalized flexible MIL-53(Fe) solids has been evaluated through a combination of in situ X-ray power diffraction, adsorption calorimetry, IR spectroscopy and computer modelling. It appears that (i) strongly polar groups maintain the nonporous structure in its closed form due to strong intra-framework interactions and (ii) less polar functional groups allow only a modulation of the CO2–framework interactions, in some cases with a disappearance of the initial intra-framework μ2-OH⋯X hydrogen bonds, but do not interact directly with the CO2 molecules.

A Method for Screening the Potential of MOFs as CO2 Adsorbents in Pressure Swing Adsorption Processes

This work reports the adsorption and coadsorption data of CO(2)/CH(4)/CO mixtures on several metal-organic frameworks [MOFs; MIL-100(Cr), MIL-47(V), MIL-140(Zr)-A, Cu-btc, and MIL-53(Cr)] and compares them with reference adsorbents, that is, zeolite NaX and an activated carbon material, AC35. We also evaluate the effect of H(2)O on CO(2) adsorption and on the stability of the structures. Based on the experimental adsorption data, the performance potential of MOFs in several pressure swing adsorption processes is estimated by making a ranking of working capacities and separation factors. We discuss the separation of biogas, the purification of H(2) produced by steam reforming of methane, and the removal of CO(2) from synthesis gas in IGCC (integrated gasification combined cycle) systems. Some MOFs are very well placed in the ranking of (isothermal) working capacity vs. selectivity. Yet, performance is not the only criterion for the selection of MOFs. Ease and cost of synthesis and long-term stability are other important aspects that have to be taken into account.

Adsorption of light hydrocarbons in the flexible MIL-53(Cr) and rigid MIL-47(V) metal–organic frameworks: a combination of molecular simulations and microcalorimetry/gravimetry measurements

The adsorption of short linear alkanes has been explored in the highly flexible MIL-53(Cr) porous metal-organic framework by means of molecular simulations based on configurational bias grand canonical Monte Carlo. The unusual shape of the adsorption isotherms with the existence of steps has been successfully modelled by creating a (narrow pore, large pore) phase mixture domain, the composition of which varies with pressure. A further step consisted of combining our computational approach with several experimental tools including microcalorimetry, gravimetry and in situ X-ray diffraction, to fully characterize the adsorption behaviour of the isostructural MIL-47(V) rigid MOF, i.e. the preferential arrangement of each type of alkane inside the pores and the resulting interaction energy. Finally, relationships are established between the adsorption enthalpies and both alkyl chain length and polarisability of the alkanes that can be further utilised to predict the energetics of the adsorption process for longer alkane chains.

A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs

A novel Zr-chain based MOF, namely MIL-163, was designed and successfully synthesized using a bis-1,2,3-trioxobenzene ligand. Endowed with large square-shaped channels of 12 Å width, it shows remarkable water uptake (ca. 0.6 cm(3) g(-1) at saturating vapor pressure) and a remarkable stability in simulated physiological media, where archetypical Zr carboxylate MOFs readily degrade.