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This paper presents a study of urea SCR catalyst aging characteristics and implementation into an analytical model that complements laboratory based experiments for a dynamometer-aged SCR brick. The model calibration is based on measured data taken from a 120k-mile simulated dynamometer-aged base metal/zeolite SCR. Dynamometer aging led to non-uniform axial deterioration with more severe deactivation toward the front of the SCR brick compared to the rear. Data from a 120k-mile simulated hydrothermally oven-aged SCR (uniform axial aging) is used to establish baseline aged NOx performance and NH3 adsorption/desorption behavior. An axial deterioration factor is applied to the baseline model to account for differences between oven and dynamometer aging. The model is exercised using engine out vehicle data to examine how different aging processes (oven vs. dynamometer) affect overall NOx performance during the EPA FTP (Environmental Protection Agency Federal Test Procedure).

Promising lean NOx trap (LNT) results on lean-burn gasoline engines have encouraged the development of LNTs for diesel applications. Although the fundamentals of LNT are common for both gasoline and diesel applications, there are major differences due to the character of engine operation and control strategies. The sulfur tolerance and thermal durability of current state-of-the-art diesel LNTs under the conditions that represent the thermal and chemical conditions in diesel exhaust were investigated in a laboratory flow reactor. Sulfur poisoning and thermal aging are unavoidable factors contributing to diesel LNT deactivation. The results show that sensitivity to sulfur poisoning varies with the catalyst formulations, and in some formulations the sulfur poisoning appears reversible. However, the thermal deactivation is permanent regardless of its cause, i.e., LNT de-sulfation (deSOx) or diesel particular filter (DPF) regeneration.

An analytical model was developed to simulate both sulfur adsorption and desorption characteristics based on the laboratory determined parameters. Diesel Lean NOx Trap (LNT) was tested under laboratory conditions to examine desulfation (deSOx) characteristics. Effects of different Lean/Rich (L/R) cycling of Air-Fuel ratio during the deSOx mode were investigated. The gradient of adsorbed sulfur along the axial direction of the sample LNT was also examined. The gradient of sulfur deposit, together with different L/R cycling combinations for the deSOx mode was critical to develop the efficient sulfur removal strategies. The model considered energy and mass balances during sulfur adsorption and desorption modes to predict the catalyst temperature and the amount of sulfur adsorbed and removed. HC and CO oxidation reactions as well as the oxygen storage were considered to estimate heat generated by the exothermic reactions.