Identification of Adsorption Sites for CO2 in a Series of Rare-Earth and Zr-Based Metal-Organic Frameworks

Abstract

The adsorption of ${\mathrm{CO}}_2$ in MOF-808, NU-1000 and a series of rare-earth CU-10 analogues has been studied with first principles DFT and classical Monte-Carlo methods. DFT calculations describe the interaction of ${\mathrm{CO}}_2$ with the different metal-organic frameworks (MOFs) as physisorption, but where we can distinguish several adsorption sites in the vicinity of the metal nodes. Beyond the identification of adsorption sites, the MOFs were synthesized, activated, and characterized to evaluate their experimental $N_2$ and ${\mathrm{CO}}_2$ adsorption capacity. Classical Grand Canonical Monte-Carlo (GCMC) simulations for the adsorption of ${\mathrm{CO}}_2$ are in very good agreement with DFT results for identifying the most favored adsorption sites in the MOFs. In contrast, a rather mixed agreement between GCMC simulations and experimental results is found for the estimation of adsorption capacity of several MOFs studied toward $N_2$ and ${\mathrm{CO}}_2$ .

Keywords: CO 2 ${{\rm{CO}}_2 }$ adsorption; DFT; GCMC; MOF; isotherms.

Figure 1

MOF‐808 structure representing a spn topology a) MOF‐808‐node1 model, b) BTC linker, c) MOF‐808 unit cell, d) Zr‐node with formate capping ligand, and e) MOF‐808‐node2 model.

Figure 2

a) NU‐1000 structure representing a csq topology b) a side view of the NU‐1000 unit cell, c) H₄TBAPy linker.

Figure 3

RE‐CU‐10 structure : representing an shp topology a) RE ‐CU‐10, b) Unit cell of Y/Gd‐CU‐10, c) H TBAPy linker, d) RE ‐CU‐10, e) Unit cell of Yb‐CU‐10.

Figure 4

${\mathrm{CO}}_2$ concentration distribution within MOF‐808 at 1 and 10 bar at 298 K. The adsorption sites considered in the DFT calculations are also identified.

Figure 5

Distribution of ${\mathrm{CO}}_2$ concentration within Y‐CU‐10 at 1 bar and 10 bar at 298 K and the corresponding adsorption sites

Figure 6

Comparison of the simulated isotherm of ${\mathrm{CO}}_2$ in volumetric units (cm /cm ) with experimental data from 0 to 1 bar at 298 K for MOF‐808, NU‐1000, Y‐CU‐10, Gd‐CU‐10 and Yb‐CU‐10. (opened symbols are from experiments, filled symbols are from GCMC simulations). Crystal density was used to convert gravimetric units to volumetric units.

Figure 7

Variation of adsorption energy as a function of ${\mathrm{CO}}_2$ concentration in a Y‐CU‐10 micropore. Snapshots of the ${\mathrm{CO}}_2$ configuration at different stages of the pore filling are provided as insets.