Noble metal-exchanged small-pore molecular sieves with chabazite topology are promising materials for automotive cold-start NO x emission control applications. A combination of first-principles thermodynamics and density functional theory was applied for the prediction of monomeric palladium, platinum, and ruthenium species formed in 1Al or 2Al sites of six-/eight-membered rings of the SSZ-13 framework in the presence of SO 2 , NO, O 2 , and H 2 O at temperatures between 0 and 1100 K. Calculations using gradient-corrected Perdew−Burke−Ernzerhof (PBE) functional and hybrid Heyd−Scuseria−Ernzerhof (HSE06) functional showed that the binding energy of NO adsorbed on Pd, Pt, or Ru ions is a strong function of exchange−correlation functional. Use of the PBE functional overestimated the binding strengths of NO to Pd, Pt, or Ru ions compared to the HSE06 functional. While PBE led to 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 1Al sites tended to bind NO stronger than their counterparts in 2Al sites. Both functionals revealed that Pd and Pt ions have more similarities in terms of both NO adsorption and sulfur resistance compared to Ru ions. The results of this study are beneficial for further modeling of passive NO x adsorbers with improved properties to deliver cleaner tailpipe emissions during engine cold start.
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