Modeling the Adsorption of NO and NH3 on Fe-SSZ-13 from First-Principles: A DFT Study

Abstract

As emission standards continue to tighten, there is a critical need for more selective and efficient methods to remove NOx from the exhaust of lean-burn engines. Currently, the predominant method employed for NOx removal is through selective catalytic reduction (SCR) using ammonia as a reducing agent. Typically, Fe- and Cu-exchanged CHA catalysts (Fe-SSZ-13 and Cu-SSZ-13) are used, but much less is known about Fe-SSZ-13 as compared to Cu-SSZ-13, which has been extensively characterized via experimental and computational techniques. In this work, density functional theory (DFT) calculations were performed to determine the most likely adsorption complexes that form within the six- or eight-membered rings (6MR or 8MR) of Fe-SSZ-13. We examine both Fe2+ (as [Fe(OH)]+) and Fe3+ (as [Fe(OH)]2+) as the possible active sites. Based on our results, the most energetically favorable site lies initially within the 6MR. However, with the addition of adsorbates, we find that the 8MR sites become more energetically favo...