Passive NOx Adsorption on Pd/H-ZSM-5: Experiments and Modeling

ABSTRACT A combined experimental and modeling study of the passive NOx adsorber (PNA) is presented that advances the understanding and prediction of the effects of various operating parameters and material properties of H-ZSM-5 and Pd/H-ZSM-5. Experiments reveal the NOx uptake process to be kinetically limited and not impacted by washcoat diffusion. Two microkinetic schemes are developed to explain the NOx uptake and release and NO2 generation data. Both schemes are incorporated into a 1 + 1 D monolith model to predict and validate NOx uptake and temperature programmed desorption (TPD) data. Scheme I involves Z - [ P d O H ] + , Z - P d 2 + Z - a n d Z - P d + with Z - P d + as the strongest NO binding site. Scheme II involves reduction of PdO2 to PdO and nitrate formation. Model tuning utilizes a combination of infrared spectroscopy measurements and density functional theory (DFT) estimates of energy barriers. The model is validated at different conditions including feed parameters and Pd loading.