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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 (Oα) 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. [ABSTRACT FROM AUTHOR]

The mechanisms of medium- and low-temperature denitrations using selective catalytic reduction (SCR) by combined CO + NH3 on Mn–Ce/activated carbon (AC) catalysts and their poisoning by SO2 were investigated. Several Mn–Ce/AC catalysts prepared and then poisoned by SO2 were used in the study. The physicochemical properties of the catalysts were systematically characterized before and after poisoning, and the mechanism of SO2 poisoning was proposed. SO2 poisoning considerably affects the Mn–Ce/AC catalyst, decreasing its denitration rate from 98% to 47.9% and N2 selectivity from 96 to 85%. This can be attributed to several phenomena. SO2 poisoning increases the surface roughness of the catalyst and results in the formation of Mn(SO4)2, other sulfates, and other substances, which block the catalyst pores and reduce the content of the C and O elements on the catalyst surface as well as its specific surface area, consequently decreasing the adsorption area available for the reaction gas. Moreover, the crystallinity of MnOx on the surface of the catalyst increases, decreasing the contents of Mn4+, Ce4+ and chemosorbed oxygen. In addition, the surface functional groups, such as –COOH, –OH, and C=O, are destroyed, reducing the adsorption sites of the reaction gas and the adsorption capacity of the catalyst, consequently inhibiting the SCR reaction. Ce can reduce the effects of SO2 poisoning on the catalyst because Ce4+ can improve its oxygen storage capacity, increase the adsorption sites for the reaction gas, and react with SO2, preventing sulfate formation and pore blockage. However, excessive Ce loading causes metal agglomeration on the catalyst surface, reducing its denitration efficiency. After SO2 poisoning, the contents of Mn4+, Mn3+, and Ce4+ decreased in the Mn -Ce/AC catalysts, inhibiting the synergistic reaction between Mn and Ce, which decreased the number of oxygen vacancies and Oβ, consequently inhibit the reaction's conversion to fast selective catalytic reduction. Thus, SO2 destroyed the functional groups; occupied the oxygen vacancies and active site; and destroyed the –COOH, O–H, and C=O functional groups on the surface of the Mn–Ce/AC catalyst, reducing the acidity and number of active sites on the catalyst surface. [ABSTRACT FROM AUTHOR]