Computational and Experimental Studies on the Adsorption of CO, N₂, and CO₂on Mg-MOF-74

Abstract

Adsorption of carbon monoxide, dinitrogen, and carbon dioxide on the porous metal−organic framework Mg-MOF-74 was investigated by means of a combined methodology comprising variable-temperature infrared spectroscopy and ab initio periodic DFT-D calculations using the CRYSTAL code. Both CO and N 2 were found to form nearly linear (Mg 2+ ···CO and Mg 2+ ···NN) adsorption complexes, in contrast with CO 2, which forms an angular Mg 2+ ···OCO complex. From IR spectra recorded at a variable-temperature, the standard adsorption enthalpy (Δ H 0 ) was found to be −29, −21, and −47 kJ mol −1 for CO, N 2, and CO 2, respectively. Calculated values of Δ H 0, including an empirical correction for dispersion forces, resulted to be in a reasonably good agreement with those experimentally obtained. Calculations also showed the very significant role played by dispersion forces, which account for about one-half of the adsorption enthalpy for each of the three adsorbates, CO, N 2, and CO 2 . The results are discussed in the broader context of the adsorption of the same gases on other MOFs and also on zeolites.