A Calcium Coordination Framework Having Permanent Porosity and High CO₂/N₂ Selectivity

Abstract

A thermally stable, microporous calcium coordination network shows a reversible 5.75 wt % CO2 uptake at 273 K and 1 atm pressure, with an enthalpy of interaction of ∼31 kJ/mol and a CO2/N2 selectivity over 45 under ideal flue gas conditions. The absence of open metal sites in the activated material suggests a different mechanism for selectivity and high interaction energy compared to those for frameworks with open metal sites.

Mechanism of Carbon Dioxide Adsorption in a Highly Selective Coordination Network Supported by Direct Structural Evidence

“…[15] However, the calculated heat of adsorption for CO 2 in CaSDB (<-30 kJ mol À1 [20] ) is significantly lower than the predicted À5.6 kJ mol À1 for the molecular benzene-CO 2 complex. [15] However, the calculated heat of adsorption for CO 2 in CaSDB (<-30 kJ mol À1 [20] ) is significantly lower than the predicted À5.6 kJ mol À1 for the molecular benzene-CO 2 complex.…”

“…[6,17] Strong interactions with polarizing functional groups, as well as with open metal sites presents other drawbacks including an increase in the costs for material regeneration. [20] At 0.15 bar of CO 2 and 0.85 bar of N 2 , a typical composition of flue gas mixture from power plants, the selectivity is in the range of 48 to 85 at 298 K. CaSDB shows a reversible uptake of CO 2 of 5.75 wt % at 273 K and 1 bar pressure and 4.37 wt % at room temperature, with heats of adsorption for CO 2 and N 2 of 31 and 19 kJ mol À1 , respectively. [6,18,19] We recently described a porous framework, CaSDB (SDB: sulfonyldibenzoate, compound 1) with a high CO 2 /N 2 selectivity.…”

Solid-State NMR Investigations of Carbon Dioxide Gas in Metal–Organic Frameworks: Insights into Molecular Motion and Adsorptive Behavior

“…They possess 1-D channels with one larger rhombic pore channel along the axis of the metal clusters surrounded by smaller channels of parallelograms. 56 This series lacks polarizing functional groups that most MOFs use to increase CO 2 adsorption affinity. Instead, their channels provide small physical π-pockets established by the proximity of the conjugated orbitals of the linkers, wherein CO 2 may adsorb.…”

Probing Calcium‐Based Metal‐Organic Frameworks via Natural Abundance 43Ca Solid‐State NMR Spectroscopy

“…Activated CaSDB (Figure S7 b) features edge-sharing CaO 6 octahedra, with Ca bound to SDB linkers that were repacked after activation (Figure 2b). [17] The 43 Ca MAS NMR spectra of as-made and activatedC aSDB ( Figure 2a and b) are of relativelyl ower S/N, due to the breadtho ft he signals. As ingle 43 Ca resonance exists in as-made CaSDB at d iso = À12.9(5) ppm (Table 1), in agreement with the crystal structure.…”

“…300 ppm within inorganic Ca-based materials. [9a, 14] These challenges raise the question:c an 43 Ca NMR spectra of MOFs be obtained with sufficient quality to provide direct information on Ca metal centers?We have performed an atural abundance 43 Ca magic-angle spinning( MAS) NMR study on four Ca based MOFs of varying composition and topology:C aBDC (H 2 BDC = terephthalic acid), [15] CaPDC [16] (H 2 PDC = 2,5-pyridinedicarboxylic acid), CaSDB, [17] and CaBTC [18] (H 3 BTC = trimesic acid). The advent of high magnetic fields has resulted in sensitivity enhancements for low-g unreceptiveq uadrupolar nuclei, including 43 Ca.…”