Controlling the Adsorption Enthalpy of CO₂ in Zeolites by Framework Topology and Composition

Abstract

Zeolites are often investigated as potential adsorbents for CO(2) adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra-framework cations), the CO(2) adsorption heats at low coverages vary from -20 to -60 kJ mol(-1), and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion-exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and -SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO(2) adsorption complexes are identified and discussed at the molecular level. A general model for CO(2) adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model.

Low concentration CO2 capture using physical adsorbents: Are metal–organic frameworks becoming the new benchmark materials?

“…10 The charge density is directly related to CO 2 interactions with the adsorbent framework. 11,12 (iv) Mild conditions for regeneration: The ability to regenerate the adsorbents is a key parameter in the selection of materials for CO 2 separation. Optimal interactions should be neither too weak nor too strong.…”

“…It is important to mention that similar Q st behavior was reported for MIL-100(Cr) 25 at the low coverage of 62 kJ/mol and other zeolites. [11][12] In light of the high affinity of rht-MOF-7 and Tb-fcu-MOF for CO 2 , it was reported that these materials may be used for highly selective CO 2 capture, but only for the removal of low CO 2 concentrations. Although these MOFs have very interesting properties, they may not be able to remove relatively high CO 2 concentrations, such as in the case of post-combustion capture (5-15% CO 2 ).…”

CO 2 adsorption–desorption properties of zeolite beta prepared from OSDA-free synthesis

“…2-IE is presumably due to the predominant formation of dual cation sites, in which two neighboring Na cations complementary interact with one CO 2 molecule. The possibility of CO 2 interaction with dual cations was proposed by Nachtigall and Cejka [66,69,70], in which they controlled the homogeneity of Al distribution in Na-FER (model zeolite with Si/Al ¼ 15.7) by changing the type of organic structure-directing agents during the synthesis [66]. When Al sites were distributed homogeneously in the vicinity of Na cations, one Na cation can interact with an average of one CO 2 molecule where the isosteric heat of adsorption is in the range of 42e47 kJ mol À1 (depending on Al T-site location) [66].…”

Enhanced CO2 adsorption capacity of amine-functionalized MIL-100(Cr) metal–organic frameworks

“…12,13 To overcome the drawbacks of amine aqueous solutions, several types of porous adsorbents that can reversibly capture and release CO2 (in temperature-or pressure-swing cycles) are currently under active investigation as a means to facilitate CO2 capture from flue gases of stationary sources. [14][15][16][17][18] Metal-Organic Frameworks (MOFs) have emerged as promising adsorbent materials for CO2 capture due to their high surface area, large pore volume and tunable pore surface. [19][20][21][22] The ability to design and tune the properties of MOFs makes these adsorbent materials distinct from other traditional adsorbents such as zeolites and carbon materials.…”