CO and NO Adsorptions on Different Iron Sites of Fe-ZSM-5 Clusters: A Density Functional Theory Study

Density functional theory (DFT) calculations were carried out in a study of CO and NO adsorptions on different iron sites of Fe-ZSM-5. The adsorption energies and distances were similar for CO adsorption on both small and large cluster calculations. The adsorption energies (Δ E ) and enthalpies (Δ H ) found for NO adsorption on [FeO] 1+ -ZSM-5 and [Fe(OH) 2 ] 1+ -ZSM-5 clusters were in line with the previous theoretical values. Some additional energy was required for NO and CO adsorptions on [FeO] 2+ -ZSM-5 (NO adsorption only), [FeOH] 2+ -ZSM-5, and [Fe(OH) 2 ] 2+ -ZSM-5 clusters because of their positive Δ G values. The scaled vibrational frequencies for adsorbed CO and NO molecules on Fe 2+ -ZSM-5 cluster were computed as 1870 and 2149 cm −1, respectively. These values are in good agreement with the experimental values for the Fe 2+ −CO and Fe 2+ −NO bands (1882 and 2140 cm −1, respectively). Moreover, the calculated vibrational frequency (1897 cm −1 ) for NO adsorption on the [HO−FeOFe−OH] 2+ -ZSM-5 cluster matches well with the experimental value (1892 cm −1 ).