Unlocking lattice oxygen mobility via acid etching in Co3O4/CeZrO2 for efficient passive NOx adsorption

Abstract

The development of high-performance passive NO_x adsorbers (PNAs) for efficient NO_x removal during the cold-start period (<200 °C) of diesel engines is crucial for meeting stringent emission regulations. Although active oxygen species play a critical role in the NO_x adsorption-storage capacity of PNAs, the detailed mechanism of their participation and regeneration remains insufficiently understood. In this study, an acid etching strategy was employed to modulate the Co₃O₄/CeZrO₂(Co/CZ) catalyst. The optimized Co/CZ-0.01 M exhibited a prolonged complete NO_x storage time of 211 s, 62% longer than that of pristine Co/CZ (130 s), along with an increase in NO_x desorption capacity from 79.1 µmol g⁻¹ to 150.1 µmol g⁻¹. Characterization and isotopic experiments revealed that acid etching selectively broke and weakened Co–O bonds, inducing local lattice relaxation and lowering the energy barrier for oxygen migration. These structural modifications collectively resulted in abundant oxygen vacancies and significantly enhanced lattice oxygen mobility in Co/CZ-0.01 M. The increased oxygen vacancies provided additional sites for O₂ adsorption and activation, while the improved oxygen mobility facilitated the rapid replenishment of surface oxygen species. These synergistic effects supplied abundant active oxygen species for oxidizing NO into nitrite/nitrate species, thereby optimizing the Mars-van Krevelen (MvK) pathway. This work provides fundamental insights into the dynamic role of active oxygen species in the NO_x adsorption-storage process and offers a practical strategy for designing high-performance and non-noble metal PNAs.