Revealing the Roles of Rh in Inhibiting “NO_x Puff” on the Cu/Ba-CeO₂ Catalyst during the Process of Lean NO_x Trap

Abstract

Lean NO x traps (LNTs) have proven to be efficient in mitigating NO x emissions from light-duty diesel or lean-burn engines. Nevertheless, "NO x puff" is usually observed on conventional LNT catalysts due to the release of previously stored NO x rather than reducing it during the initial lean-burn period, which significantly lowers the overall NO x removal efficiency. Thus, Rh was introduced into the Cu5Ba5Ce catalyst with an excellent NO x storage performance to address the "NO x puff" issue in this work. The onset of the "NO x puff" on Rh1Cu5Ba5Ce during the initial phase of the rich-burn period is effectively controlled. The concentration of the "NO x puff" is decreased from 1200 ppm on Cu5Ba5Ce to 400 ppm on Rh1Cu5Ba5Ce. Moreover, the NO x storage and removal efficiency are improved from 75.2 and 22.0% on Cu5Ba5Ce to 99.1 and 74.2% on the Rh1Cu5Ba5Ce catalyst, respectively. The concentration of oxygen vacancies is increased, and the adsorption behavior of CO is adjusted by the introduction of Rh. The concentrations of Ce 3+ , Cu 2+ , and surface oxygen are promoted, which are contributed to enhance the amount of NO x adsorption and storage. The introduction of Rh compensates for the insufficient reduction capability of the Cu5Ba5Ce catalyst during the initial lean-burn period, enhancing the reactivity of NO x and CO. Finally, the "NO x puff" was inhibited by NO catalytic reduction with CO to improve NO x removal efficiency. This study provides an efficient strategy to address "NO x puff" issues on Ce-based LNT catalysts.