Performance-enhanced catalysts derived from spent ternary lithium-ion batteries for simultaneous removal of NOx and VOCs

Abstract

The surge in demand for lithium-ion batteries in the electric vehicle industry signals the imminent retirement of large quantities of spent lithium batteries. Consequently, the recovery of valuable metal elements from spent batteries has become a major research focus. In this study, deep eutectic solvents were employed as green leaching and precipitation agents to selectively separate lithium from nickel, cobalt, and manganese and synthesize Mn_aCo_bNiO_x catalysts for the simultaneous removal of NO_x and benzene. This work reveals the effect of the lithium ion removal process on catalytic materials. Compared to traditional metal salt synthesis methods, the delithiation process of the raw material not only affects the catalyst's structure but also introduces more oxygen vacancy defects and active oxygen species, enhancing its low-temperature reducibility, surface acidity, and catalytic activity. The catalyst exhibits outstanding catalytic performance in the synergistic removal of NO_x and VOCs, achieving over 90% denitrification efficiency in a wide temperature range of 100–270 °C and 90% benzene removal at 180 °C. In situ DRIFTS results reveal that benzene adsorption occupied the Lewis acid sites of the catalyst, inhibiting the adsorption of NH₃ and NO. Meanwhile, at low temperatures (<140 °C), the reaction between benzene and NO plays a dominant role in promoting benzene oxidation. However, at higher temperatures, the competitive adsorption of NH₃ and NO for active oxygen inhibits the oxidation of benzene into intermediates, ultimately suppressing its complete oxidation to CO₂.