Abstract
Passive NOx adsorption (PNA) is a novel technology to control NOx emissions during cold start. However, the recent generation of PNA material, Pd/zeolite, suffers from major degradation under high CO concentrations. In this work, we developed a novel form of Pd/SSZ-13 by using a freeze-drying process after incipient wetness impregnation. This Pd/SSZ-13 showed a better stability than the sample synthesized by the common process. Several characterization measurements were conducted and it was found that the Pd sites on the freeze-dried sample were more resistant towards CO-induced agglomeration. By combing in-situ characterization and kinetic modeling, we found that the freeze-dried Pd/SSZ-13 had more ion-exchanged Pd sites, which provided greater resistance towards the CO-induced Ostwald ripening process, and consequently suppressed the sintering behavior under a high CO concentration. This material offers a potentially improved stability of PNAs under extremely high CO concentration pulses from incomplete diesel combustion during engine cold start.
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