Effects of C12H26 and O2 on NO Uptake on Pd/SSZ-13: Experiments and Modeling

Addressing NO_x (NO+NO₂) emissions during vehicle cold start (< 150^oC) remains a major challenge. Passive NO_x Adsorber (PNA) is a potential solution to reduce NO_x emissions during the cold start period. Therefore it is important to study the effects of different exhaust components on NO_x uptake on PNA. The objective of the current study is to understand the impacts of C₁₂H₂₆ (dodecane) and O₂ on NO_x uptake and release. Systematic experiments are conducted with mechanistic-based modeling to elucidate the underlying mechanism for coupled C₁₂H₂₆, O₂ and NO uptake on Pd/SSZ-13.

In our recent study we developed a one-dimensional two-phase transient monolith model containing a mechanistic-based microkinetic scheme to explain the NO_xuptake and release over different PNA materials [1,2]. Model involves Z^-[PdOH]⁺,Z^-Pd²⁺Z^- and Z^-Pd⁺ as active sites. Here we will present experimental and modeling studies on the uptake of NO in the presence of C₁₂H₂₆ over a Pd/SSZ-13. When a co-feed containing C₁₂H₂₆ and NO is supplied to Pd/SSZ-13 catalyst, compared to NO-only feed, the NO uptake is unaffected but during the subsequent temperature ramp, the release of trapped NO is delayed to over 220^oC from 175^oC. The release delay is beneficial for PNA performance as the primary NO_x aftertreatment technology Selective Catalytic Reduction (SCR) is not operated below 200^oC. Oxidation of C₁₂H₂₆ leads to the generation of partial oxidation product CO. Carbon monoxide binds strongly to Pd sites with NO and can delay NO release. The developed model was extended to include the effects of C₁₂H₂₆ on NO uptake and release. Some of the modelling results are shown in Fig. 1. The model is validated at different uptake temperatures, temperature programmed desorption (TPD) ramp rates, and feed flow rates, affording its use to validate the experimental findings and to identify optimal operating strategies.