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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.