02491nas a2200157   4500008004100000022001400041245012700055210006900182260000900251300001600260490000800276520186900284100002902153700002602182856012502208       2024                        eng d  a1932-744700aFirst-principles simulation of active site selectivity for CO2 and H2 adsorption on Mg(OH)+/Mg2+ and Ca(OH)+/Ca2+ zeolites0 aFirstprinciples simulation of active site selectivity for CO2 an  cDEC   a21659-216710 v1283 a<p>
	One very effective strategy for addressing global warming and transitioning to sustainable energy sources is selective CO2 separation over H-2. Porous materials, particularly zeolites, have demonstrated enormous potential for energy-efficient separation techniques combined with storage. By altering interactions at cation-binding sites, zeolite's gas adsorption characteristics toward carbon capture can be improved. In this study, Mg and Ca are assessed as extra-framework cations in divalent (Ca2+, Mg2+) and monovalent states (Ca(OH)(+), Mg(OH)(+)) in faujasite and chabazite zeolites for CO2 capture over H-2. The study also explores the impact of mixed cations, viz., a combination of both Ca2+ and Mg2+ in the framework, on their selective adsorption potential. This study uses DFT with dispersion corrections to calculate adsorption energies, enthalpies, and Gibb's free energies of adsorbed CO2 and H-2 molecules. Among the dispersion parameters evaluated, viz., D4, TS/HI, and MBD, D4 approaches experimental accuracy. In general, the adsorption trend obtained for CO2 is Mg FAU &gt; Ca FAU &gt; Mg CHA &gt; Ca CHA &gt; Mg(OH)(+) FAU &gt; Ca(OH)(+) FAU &gt; Mg(OH)(+) CHA &gt; Ca(OH)(+) CHA. The heats of adsorption using PBE+D4 for CO2 are -46 kJ/mol for Ca FAU and -10 kJ/mol for Ca(OH)(+) FAU, respectively. These values closely align with the experimental results of -45 and -6 kJ/mol, respectively, within a chemical accuracy limit of +/- 4 kJ/mol. The relative adsorption energies suggest that for both FAU and CHA, there exists a minimum difference of 26 kJ/mol in adsorption energies between CO2 and H-2. Hence, this piece of work highlights that FAU with Ca and Mg as extra-framework cations in a six-membered cage can be a viable substitute to replace, the current best candidate in literature, viz., Li+, for selective CO2 capture.</p>
1 aSamal, Pragnya, Paramita1 aKrishnamurty, Sailaja  uhttps://library.ncl.res.in/content/first-principles-simulation-active-site-selectivity-co2-and-h2-adsorption-mgohmg2-and