Improving NOx storage and CO oxidation abilities of Pd/SSZ-13 by increasing its hydrophobicity

Do Heui  Kim, Seoul National University

When Pd is atomically dispersed in hydrophilic SSZ-13, it is readily hydrated to form Pd-hydrate ions. The formation of Pd-hydrate ions from dehydrated Pd ions has been reported to greatly hamper the NOx storage capacity. In this study, the concentration of dehydrated Pd ions in Pd/SSZ-13 was increased by making the sample more hydrophobic. Hydrophobic Pd/SSZ-13 was synthesized by inducing dealumination in hydrophilic Pd/SSZ-13 through the hydrothermal treatment at 750 oC, while the atomic dispersion of Pd was confirmed in both hydrophilic and hydrophobic Pd/SSZ-13 samples. Hydrophobic Pd/SSZ-13 displayed the improved NOx storage capacity (approaching the theoretical limit of NOx/Pd = 1.0) in the desirable NOx desorption temperature range (below 350 oC) as well as the enhanced rate of NOx adsorption than hydrophilic Pd/SSZ-13. Moreover, hydrophobic Pd/SSZ-13 also displayed the better CO oxidation ability (shifting the temperature of 50% CO conversion to the lower temperature by 71 oC) than hydrophilic Pd/SSZ-13. These improvements would have the important implications in developing Passive NOx Adsorbers (PNAs).