Unveiling the Mechanism of NO Reduction by CO over Highly Dispersed Zero-Valent Copper Catalysts: Experiments and DFT...

Efficient transition-metal-based catalysts for low-temperature NO reduction remain a significant challenge. In this study, an efficient, highly dispersed zero-valent copper (Cu⁰) supported on activated carbon catalyst was prepared, exhibiting high NO reduction performance at 200 °C, with 80% NO conversion and 100% N₂ selectivity. The calcination temperature plays a crucial role in determining the composition and dispersion of catalysts, which subsequently affects their catalytic performance in NO reduction. At lower calcination temperatures, incomplete reduction of the active components results in a reduced catalytic activity. Conversely, higher calcination temperatures lead to catalyst agglomeration, increasing the level of CO adsorption on the catalyst surface, which subsequently inhibits the NO reduction. When the reaction temperature is over 300 °C and the O₂/CO ratio is ≤0.5, the activity of the Cu-BAC-500 catalyst for NO reduction by CO is scarcely affected by O₂. The reaction temperature alters the NO reduction mechanism. The reaction mechanism in this study was primarily simulated under oxygen-free conditions. At lower temperatures, the mechanism involves the coadsorption of NO, which decomposes to form N₂O. This N₂O is then directly reduced by CO to produce N₂. When the reaction temperature is above 300 °C, in addition to the aforementioned pathway, a new route emerges where adsorbed NO is directly reduced by CO to generate CO₂ and surface-active N* species. These N* species then adsorb NO, forming N₂O, which is further reduced by CO to form N₂. This study presents novel copper-based catalysts and offers a strategy for efficient low-temperature NO reduction.