Novel layered double hydroxide-based passive NOx adsorber: Synergistic effects of Co and Mn on low-temperature NOx storage and regeneration

초록

Passive NOx adsorber (PNA) is an efficient strategy for reducing vehicular NOx emission during cold-start period, and current studies on PNA development are limited to materials containing precious metals (Pt, Pd, and Ag, etc.). Herein, Co-Mn-Mg-Al mixed metal oxides were prepared from layered double hydroxides (LDHs) and utilized as a new type of PNA. Although Co-Mg-Al oxides exhibited excellent NOx adsorption capabilities because Co species promoted the generation of active oxygen species, their NOx adsorption performance dete-riorated substantially with decreasing adsorption temperature below 150 & DEG;C and they required high temperatures over 400 & DEG;C to release the adsorbed NOx. Conversely, Mn-Mg-Al oxides retained their adsorption performance regardless of adsorption temperature and allowed for NOx desorption at relatively low temperatures by decreasing the thermal stability of the adsorbed NOx species. Notably, Co-Mn-Mg-Al mixed oxides exhibited high NOx adsorption performance at low temperatures between 50 and 150 & DEG;C and were passively regenerated via thermal treatment within a temperature range of 200-350 & DEG;C owing to the synergistic effects of Co and Mn. The developed LDH-based PNA materials presented excellent cyclic NOx adsorption performances for long-term operation, and dynamic tests indicated that NOx adsorbed onto Co-Mn-Mg-Al mixed oxides was effectively released with increasing temperature even in the presence of NO and O2.

키워드