The mitigation of cold-start emissions involves the development of passive NO x adsorbers (PNA) systems that store NO x at low temperature, being designed to release the trapped NO x at higher temperatures, where downstream NO x reduction catalysts are efficient. Pd-based zeolites (BEA, SSZ-13) with different SAR (Si-to-Al ratio) were used for PNA investigation, and Pd/Ce/Al 2 O 3 catalyst was used as a reference for comparison. In this study, NO x adsorption is investigated at low temperature (80 °C) and it is released during a temperature ramp (to 400 °C) under various gas feed composition. Moreover, detailed characterization was performed using BET, XRD, XPS, TPO, STEM and ICP-SFMS and the stored NO species was studied using in-situ DRIFTS. The addition of CO to the storage mixture resulted in that for Pd/zeolites with low and medium SAR the binding energy for NO was increased. In addition, NO was stored in larger quantities, especially for the Pd/SSZ-13 samples. However, for Pd/BEA (SAR = 300) no such stable NO species was formed and for Pd/Ce/Al 2 O 3 the CO addition was even negative. Moreover, in-situ NO DRIFTS showed that there was large amount of nitrosyls on ionic palladium for the Pd/zeolites with low and medium SAR, indicating that a significant fraction of the palladium was in ionexchanged positions, while this peak was small for the Pd/BEA (SAR = 300) and non-existing for Pd/Ce/Al 2 O 3. Thus, CO addition is beneficial for Pd species that are in ion-exchanged positions, but this is not the case for Pd particles and this can explain the observations that CO is only beneficial for Pd/zeolites with low and medium SAR. Moreover, experiments with similar SAR [Pd/BEA (SAR = 25) and Pd/SSZ-13 (SAR = 24)], showed that there is larger stability of the stored NO x in the small pore Pd/SSZ-13.

Commercial lean NO x trap (LNT) catalysts were aged and characterized to elucidate the effect of aging on their performances and examine the deactivation of a rapid-aged catalyst toward an improved correlation with respect to a vehicle-aged catalyst. Detailed characterization studies were carried out on the flow reactor with small cylindrical cores extracted from the commercial LNT catalysts. Physicochemical characterization techniques were also implemented. The catalyst evaluation revealed that aging resulted in a significant deterioration of NO x storage and reduction functions as a consequence of precious metal sintering, loss of surface area of the NO x storage and support materials, phase transitions of the adsorber compounds, and large accumulation of poison species. Among the aged samples examined, the middle (lengthwise) vehicle-aged sample showed the highest NO x conversion, while the oven-aged catalyst was the most active of the aged samples for water gas shift reaction and oxygen storage.

Carbon monoxide (CO) oxidation is one of the more widely researched mechanisms given its pertinence across many industrial platforms. Because of this, ample information exists as to the detailed reaction steps in its mechanism. While detailed kinetic mechanisms are more accurate and can be written as a function of catalytic material on the surface, global mechanisms are more widely used because of their computational efficiency advantage. This paper merges the theory behind detailed kinetics into a global kinetic model for the singular CO oxidation reaction while formulating expressions that adapt to catalyst properties on the surface such as dispersion and precious metal loading. Results illustrate that the model is able to predict the light-off and extinction temperatures during a hysteresis experiment as a function of different inlet CO concentrations and precious metal dispersion.

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