First Principle Study of Catalyst’s Influence on Self-Inhibition Effect and By-Products Formation of Lean NOx Trap

Lean NOx trap is a dedicated DeNOx catalyst for lean hybrid gasoline engines. Noble metals (usually platinum group metals) play the role of catalytic sites for NOx oxidation and reduction, which have significant impact of the performance of LNT. This work focuses on the influence of noble metal catalysts on self-inhibition effect from the view of competitive adsorption between NO and CO, and investigates the influence of CO self-inhibition effect on the main by-product of LNT: N₂O formation. Adsorption configurations for NO, CO and N₂O on noble metal clusters supported by γ-Al₂O₃(100) are confirmed. For detailed investigation, electron structures are analyzed by investigating Bader charge, DOS (density of state), charge density differences and COHP (crystal orbital Hamilton population) of selected configurations.The results show that CO self-inhibition effect is caused by competitive adsorption between CO and NO. The essence of competitive adsorption between CO and NO is that adsorption process of CO and NO on catalytic sites is similar. Excessive adsorption of CO on the catalytic site occupies the catalytic site and limits the NO adsorption and subsequent processes, making NO conversion efficiency decrease. Competitive adsorption between CO and NO will limit NO adsorption and dissociation, thus limiting N₂O formation. Meanwhile, stronger adsorption of N₂O on catalytic sites will make N₂O desorption difficult.