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[Display omitted] • Different crystalline phases of MnO 2 catalysts were prepared via a facile hydrothermal method. • γ-MnO 2 catalyst exhibited the highest NO conversion and CO conversion. • γ-MnO 2 catalyst possessed abundant surface adsorbed oxygen and Mn4+ species. • Reaction mechanism model of γ-MnO 2 catalyst for NH 3 -SCR and CO oxidation was proposed. It is indeed a challenging problem to simultaneously remove NO and CO from the steel sintering flue gas, in which a bifunctional catalyst has proven to be an efficient solution for removing both pollutants at low temperature. In this study, four different crystalline phases of MnO 2 (α-, β-, γ-, and δ-) catalysts were synthesized via a facile hydrothermal method, and the effects of their crystal structure, morphology, and physicochemical properties on the catalytic performance for NO reduction and CO oxidation were elucidated. The results indicated that γ-MnO 2 catalyst exhibited the best catalytic activity, achieving 90% NO removal efficiency and 82% CO conversion rate at 175 °C. Reaction kinetics confirmed that γ-MnO 2 catalyst exhibited a lower Ea for both NO reduction and CO oxidation compared to α-MnO 2 , β-MnO 2 and δ-MnO 2 catalysts. Meanwhile, the interaction of between NH 3 -SCR and CO catalytic oxidation reactions over the catalysts was also studied. Intriguingly, it was found that the presence of CO enhanced the catalytic activity of γ-MnO 2 catalyst in the NH 3 -SCR reaction. The results of NO + O 2 -TPD and in situ DRIFTS experiments revealed that CO contributed to the adsorption and oxidation of NO, thus promoting the L-H pathway over γ-MnO 2 catalyst. Finally, a possible mechanism model for simultaneous removal of NO and CO over γ-MnO 2 catalyst was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • CuO modified CeFe catalysts were prepared via wet impregnation method. • CuO could improve de-NO x and CO oxidation activities for CeFe catalyst. • CuO could increase surface acidity, Ce3+/(Ce3+ + Ce4+) ratio and surface adsorbed oxygen of CeFe catalyst. • Reaction mechanism model of CuO over CeFe catalyst for NH 3 -SCR and CO oxidation was proposed. Nitrogen oxides (NO x) and carbon monoxide (CO) coexisted in numerous industrial waste gases. And selective catalytic reduction of NO x with ammonia (NH 3 -SCR) and CO catalytic oxidation were considered as the effective technologies for simultaneous elimination of NO x and CO, respectively. However, an efficient bifunctional catalyst was crucial for achieving simultaneous removal of NO x and CO. Herein, we developed a series of Cu-modified CeFe catalysts for simultaneous removal of NO x and CO. The results demonstrated that 5Cu-CeFe catalyst presented the best catalytic performance, achieving approximately 81% NO x removal efficiency and nearly 99% CO conversion rate at 200 °C under a gas houely space velocity of 90,000 h−1. The XPS analysis demonstrated that copper oxides played a critical role in promoting the formation of Ce3+ and O β , thereby facilitating the NH 3 -SCR catalytic performance and CO catalytic oxidation. Moreover, the copper oxide modification of CeFe catalyst attained a trade-off between the surface acidity and redox ability, resulting in improving adsorption and activition capacity of the reactant gases. In situ DRIFTS experiments revealed that the NH 3 -SCR process primarily obeyed the Eley-Rideal (E-R) pathway over both CeFe and 5Cu-CeFe catalysts, while Langmuir-Hinshelwood (L-H) pathway hardly participated in NH 3 -SCR process. The presence of Cu+–CO species and surface lattice oxygen was crucial for CO oxidation, and both Mars-van Krevelen (M−K) and L-H pathways might be involved in the CO catalytic oxidation process over 5Cu-CeFe catalyst. [ABSTRACT FROM AUTHOR]

• Different precipitants were used to prepare bifunctional MnO x catalysts via a co-precipitation method. • Mn-AC catalyst exhibited the highest NO conversion and CO conversion. • The presence of CO had an active influence on NO reduction over Mn-AC catalyst. • Reaction mechanism model of bifunctional MnO x catalysts for NO reduction and CO oxidation were proposed. In this work, ammonium carbonate, sodium hydroxide, and ammonium hydroxide were selected as the precipitants to prepare bifunctional MnO x catalysts via the PEG-assisted co-precipitation method. SEM analysis revealed that MnO x catalysts prepared with ammonium carbonate (AC) displayed a spherical morphology with relatively large size, whereas the catalysts synthesized with sodium hydroxide (SH) and ammonium hydroxide (AH) exhibited polyhedron shapes with smaller size. The results demonstrated that Mn-AC catalyst presented superior catalytic activity for both NO reduction and CO oxidation, achieving 89% NO conversion at 100 ºC and over 80% CO conversion at 200 ºC, outperforming Mn-SH and Mn-AH catalysts. Mn-AC catalyst possessed more abundant Mn4+ species and surface chemisorbed oxygen than Mn-AH and Mn-SH catalysts, which served as a significant motivation for the difference in catalytic activity. Additionally, Mn-AC catalyst exhibited stronger surface acidity, which facilitated the adsorption and activation of ammonia species in the NH 3 -SCR reaction. Furthermore, in situ DRIFTS experiment suggested that the pre-desorption of CO promoted the adsorption and activation of NO. On this basis, the possible mechanism model of three precipitants on bifunctional MnO x catalysts was proposed. [Display omitted] [ABSTRACT FROM AUTHOR]