CO2, N2 and H2 adsorption in Zn2+-containing zeolites and metal–organic frameworks

We employ a chemically accurate (±4 kJ mol−1) embedding approach to calculate enthalpies for CO2, N2, and H2 adsorption in the Zn2+-containing zeolites FAU and CHA, and for CO2 and H2 in the metal–organic frameworks (MOFs) Zn-MOF-74 and CALF-20. Using MP2 as the high-level method and PBE+D4 as the periodic low-level method (MP2:PBE+D4), we obtain CO2 adsorption enthalpies of −46, −34, and −36 kJ mol−1 for Zn-CHA, Zn-MOF-74, and CALF-20, respectively, all within chemical accuracy limits of the experimental values of −42, −30, and −39 kJ mol−1. For CO2 in Zn-FAU, where no experimental data exist, we provide an MP2:PBE+D4 prediction of −49 kJ mol−1. For N2, we predict MP2:PBE+D4 adsorption enthalpies of −41 and −39 kJ mol−1 in Zn-CHA and Zn-FAU, respectively. CO2 adsorption is stronger in the zeolites than in the studied MOFs. Across all systems, CO2 adsorption tends to be stronger than N2 adsorption and both are largely favoured over H2. We observe inconsistent accuracy of PBE+D4 for the two MOFs, despite their similar characteristics, underscoring the need for high-level approaches in predictive screening. Additionally, we conclude that Zn2+ cations with open coordination sites act as the primary binding sites and that these cations preferentially occupy 6-membered rings in zeolites.