Passive NOx adsorbers (PNAs) using Pd/zeolites have shown promise in NOx emission control at temperature (T) &lt; 200 oC, where downstream SCR catalysts remain less active. However, most adsorbed NOx over monometallic Pd/BEA is desorbed at T &lt; 200 oC when both CO and H2O are present in the exhaust feed. Incorporation of a second metal in Pd/BEA can alter the Pd species and thus tune the NOx adsorption capacity and desorption temperature. Herein, the NOx desorption temperature was tuned by incorporating Cu in Pd/BEA PNAs. Specifically, the NOx desorption temperature of monometallic Pd(0.5)/BEA and Cu(1.0)/BEA was compared to that of bimetallic Pd(0.5)Cu(x)/BEA (x = 0.15 - 0.75 wt.%) over five consecutive NOx adsorption/desorption cycles in the presence of CO and H2O. The NOx/Pd ratio (NOx desorbed at T &gt;200 oC) over monometallic Pd(0.5)/BEA decreased from 0.18 to 0.04 from the 1st to 5th NOx adsorption/desorption cycle. Cu incorporation led to a significant increase in the amount of NOx desorbed at T &gt;200 oC (Fig. 1). NOx/Pd ratio (NOx desorbed at T &gt;200 oC) in the 5th cycle increased from 0.04 to 0.25 to 0.42 when the Cu loading in Pd(0.5)/BEA increased from 0 to 0.15 to 0.3 wt.%. Increasing the Cu loading further to 0.6 and 0.75 wt.% led to a decrease in the NOx/Pd ratio. In this work, the NOx desorption mechanism over Pd/BEA and PdCu/BEA are investigated using a series of microreactor and in-situ CO, NO diffuse reflectance infrared Fourier transform spectroscopy experiments.

Breaking the NOx desorption temperature limit of Pd/BEA passive NOx Adsorbers by second metal incorporation

ACS Spring 2022

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