(173w) Role of Co and Mn on Low-Temperature NOx Adsorption Behaviors of Layered-Double-Hydroxide-Based Passive NOx Adsorber

Nitrogen oxides (NO_x) emitted from internal combustion engine vehicles have contributed to environmental problems, such as acid rain and photochemical smog. Selective catalytic reduction with NH₃ (NH₃-SCR) is a great way to reduce NO_x emission once the vehicle engine temperature reaches the operating temperature. However, the performance of current NH₃-SCR system is insufficient at low temperatures, which leads to increase in NO_x emission during “cold-start” period. Incorporation of passive NO_x adsorber (PNA) is a potential solution to achieve high NO_x removal efficiency in wide temperature range. PNA temporarily stores NO_x during cold-start to suppress the NO_x emission at low temperatures. As temperature increases, the adsorbed NO_x is thermally released and subsequently reduced by downstream NH₃-SCR. The general formulation of PNA includes precious metal (Pt, Pd or Ag) on zeolites or amorphous oxides. Herein, we propose a new type of non-precious metal PNA using layered double hydroxides (LDHs). LDHs produce homogeneous mixed metal oxides with high surface area and strong basicity, which are proper for NO_x adsorption, by calcination. The properties of metal oxides can be easily adjusted by introducing various metal ions. In this study, it was found that Mn-containing mixed oxides exhibited excellent NO_x storage and regeneration performance, and the role of Mn on PNA performance was investigated using in-situ DRIFTS analysis.