Enhancing the K-resistance of MnOx catalysts via Ce and Nb co-doping for low-temperature NOx elimination

Manganese oxide (MnO_x) catalysts are promising for low-temperature NH₃-Selective Catalytic Reduction (NH₃-SCR) with their superior catalytic performance. However, the presence of alkali metals in flue gases, particularly potassium (K), leads to catalyst deactivation and limits their industrial application. This study investigates the synergistic effects of Ce and Nb doping on the K resistance and low-temperature NH₃-SCR activity of MnO_x. The surface acidity and redox properties of MnO_x were modulated by Ce and Nb modification. In addition, the phase structure, surface state and active sites of the catalysts were characterized before and after K poisoning. The results indicated that Nb_0.05Ce_0.05MnO_x exhibited exceptional low-temperature performance, achieving over 90 % NO conversion at 125-250°C, along with significant resistance to K poisoning·NH₃-TPD and in-situ experiments revealed that the loss of acid sites is the primary cause of K poisoning. The mechanism follows the L-H mechanism with L-acid sites as the main active sites on the catalyst surface and bridging nitrate as the key intermediate state. This research provides valuable insights into enhancing the industrial applicability of MnO_x-based catalysts for low-temperature denitrification.