Unusual water-assisted NO adsorption over Pd/FER calcined at high temperatures: The effect of cation migration

Moisture contained in vehicle exhaust gas normally degrades the capacity and efficiency of Pd ion-exchanged zeolites as NOx adsorbents by competitive adsorption on active sites. Here, we report a counterexample to this general proposition, which moisture facilitates storage NO nitrosyl complex hydrated ions high temperature calcined FER-type zeolites. Divalent Pd2+ cations upon elevated (>800 °C) calcination occupy sterically constrained cationic position zeolite framework, become inactive for probe molecules such NO. These ‘hidden’ ions, however, are accessible when is hydrated, but readily release dehydration proceeds. Combined systematic situ infra-red data with X-ray diffraction Rietveld analyses reveal that temperature-induced relocation more stable positions located near 6-membered ring ferrierite cage responsible behavior.