Enhancing the NOx storage and hydrothermal stability of Pd/SSZ-13 passive NOx adsorbers by regulating the Al distributions

Pd/SSZ-13 with different Al distributions were hydrothermally synthesized and utilized as passive NOx adsorbers (PNA). The characterization results indicated that more concentrated Al distribution can not only improve the ion-exchanged level of Pd but also generated more Z2Pd2+ sites at six-member rings. Thus, as revealed by NOx adsorption experiments, samples with more Z2Pd2+ sites showed high NOx storage capacity as well as stronger water resistance. Besides, 84.8 % adsorption capacity of this sample was retained after hydrothermal aging treatment. On the other side, Pd existed as [Pd(OH)]+ sites on SSZ-13 with isolated Al as the majority. These sites were vulnerable to H2O and less stable. Seriously Pd agglomerated was observed on the aged Pd/SSZ-13 with less paired Al. This study revealed that proper Al distribution on SSZ-13 could significantly improve the performance and stability of the catalyst and provided a new direction for the design of PNA catalysts.

Automated summary

This study revealed that proper Al distribution on SSZ-13 can significantly improve the performance and stability of PNA catalysts, by enhancing ion-exchange level and increasing Z2Pd2+ sites, which leads to enhanced NOx adsorption capacity and water resistance.