Computational screening analysis of iron zeolites for selectively capturing NOx and CO over H2O and CO2†

Abstract

This work aims at shedding light on the capture mechanisms of toxic atmospheric pollutants by zeolites. A comprehensive computational investigation has been conducted to evaluate the interaction energies of NO, NO₂, CO, CO₂, and H₂O with Fe²⁺ supporting both chabazite and mordenite zeolites using periodic density functional theory calculations. Si/Al ratio sets of {11, 5, 3} and {23, 11, 5} have been respectively chosen for chabazite and mordenite. Our findings show that both systems exhibit a thermodynamic preference for bonding NO and NO₂ over H₂O and CO₂. Moreover, ab initio molecular dynamics simulations at 300 K for the Fe-chabazite system with Si/Al = 3 confirm the adsorption of NO, NO₂ and CO even in the presence of H₂O molecules, and the radial distribution function was employed to understand how steam affects NO, NO₂ and CO bonding. CO₂ co-adsorption was eventually neglected in our study due to its low interaction energy. Finally, Bader charges and charge density differences were calculated to analyze bond elongation after adsorption and account for the regeneration of the substrate. Results show that low Si/Al ratios enhance the affinity for NO and NO₂ and favour the regenerability of the adsorbent. This study demonstrates that the utilization of zeolites containing iron as the compensating cation presents promising potential as effective adsorbents for capturing NO_x and CO in the presence of H₂O and CO₂ originating from diesel engine emissions within confined work environments.