Computational Study of Noble Metal CHA Zeolites: NO Adsorptionand Sulfur Resistance

Noble metal-exchanged small-pore molecular sieves withchabazite topology are promising materials for automotive cold-start NOxemission control applications. A combination offirst-principles thermody-namics and density functional theory was applied for the prediction ofmonomeric palladium, platinum, and ruthenium species formed in 1Al or 2Alsites of six-/eight-membered rings of the SSZ-13 framework in the presenceof SO2, NO, O2, and H2O at temperatures between 0 and 1100 K.Calculations using gradient-corrected Perdew-Burke-Ernzerhof (PBE)functional and hybrid Heyd-Scuseria-Ernzerhof (HSE06) functionalshowed that the binding energy of NO adsorbed on Pd, Pt, or Ru ions is astrong function of exchange-correlation functional. Use of the PBEfunctional overestimated the binding strengths of NO to Pd, Pt, or Ru ions compared to the HSE06 functional. While PBE ledto the adsorption of two NO per Pd, Pt, or Ru ion, HSE06 predicted the adsorption of a single NO. Isolated Pd, Pt, or Ru ions in 1Alsites tended to bind NO stronger than their counterparts in 2Al sites. Both functionals revealed that Pd and Pt ions have moresimilarities in terms of both NO adsorption and sulfur resistance compared to Ru ions. The results of this study are beneficial forfurther modeling of passive NOxadsorbers with improved properties to deliver cleaner tailpipe emissions during engine cold start