Coupled uptake and conversion of C12H26 and NO on Pd/SSZ-13: Experiments and modeling

Abstract

The uptake of NO in the presence of C12H26 (dodecane) and H2O over a Pd/SSZ-13 washcoated Passive NOx Adsorber (PNA) monolith is reported. When a co-feed containing C12H26 and NO is supplied to an unsaturated (with C12H26) sample, the NO uptake is unaffected but during the subsequent temperature ramp the release of trapped NO is delayed from 175°C to over 220°C. The release delay is beneficial for PNA performance as the primary NOx aftertreatment technology, Selective Catalytic Reduction (SCR), is not operated below 200°C. However, pre-saturation of C12H26 followed by the same NO and C12H26 co-feed results in a decrease in the NO uptake compared to the NO-only feed. We conjecture that C12H26 pre-adsorbed on the exterior surface of the sample blocks NO access to the pores, decreasing the number of available sites for NO uptake. Oxidation of C12H26 leads to the generation of partial oxidation product CO at lower temperatures (<250°C) and deep oxidation product CO2 at higher temperatures. Carbon monoxide binds strongly to Pd sites with NO and can delay NO release. A Pd/SSZ-13 washcoated monolith model developed in an earlier study [Ambast et al., Appl. Catal. B. Environmental (2021) [1]] is upgraded to include C12H26 storage, release, and conversion. Through a systematic combination of judicious experiments, model tuning, and validation, we provide evidence for the underlying NO uptake and release mechanisms in the presence of C12H26.