Mechanism of NO removal by CO + NH3 coupling in iron–manganese/activated carbon catalysts at medium and low temperatures

Abstract

In this study, Fe–Mn/activated carbon (AC) catalysts were prepared to investigate the CO + NH₃ coupling for deducing the NO removal mechanism by iron and manganese supported on AC catalysts under moderate to low-moderate aerobic conditions. Through the catalyst surface morphology, phase analysis, and other test results, we propose a mechanism for the CO + NH₃ coupling that results in NO removal at medium to low temperatures. The results indicate that NO conversion initially decreases and then increases in the range of 150–300 °C with 9% oxygen content. The NO conversion of the 3.5Fe–7.0Mn/AC catalyst reached 95%, surpassing other catalysts, with an inflection point near 230 °C. Characterization of the 3.5Fe–7.0Mn/AC catalyst revealed a smooth surface, uniform pore development, a high number of micro and medium pores, and elevated surface oxygen species (O_α) content. Mn₂O₃ and Fe₃O₄ are uniformly distributed on the surface, enhancing the reaction gas contact area and thereby improving NO conversion. Fe²⁺ is identified as the primary active site for NO removal. Increased Mn loading raises the Fe²⁺ and Mn³⁺ levels, with Mn³⁺ improving the NO conversion rate.