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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]

• Toxicity effects of lead salt species on Mn-Ce/Cu-X catalyst were investigated. • Pb species might primarily occupy the active site of Mn and Cu species. • PbCl 2 and PbNO 3 species predominantly affected the Brønsted acid sites. • PbSO 4 and PbCO 3 species mainly impacted the adsorption of NO + O 2. For the sintering flue gas in steel industry, selective catalytic reduction (SCR) of NO x using NH 3 at low temperature in the presence of heavy metals is still a challenge. In this study, the toxicity effects of lead salt species (PbCl 2 , Pb(NO 3) 2 , PbSO 4 , PbCO 3) on Cu-exchanged zeolite X doped with Mn-Ce catalysts (MCCX) were investigated. All catalysts exhibited poor low-temperature SCR performance within 75–225 °C after Pb poisoning, and the poisoning effects of PbCl 2 , Pb(NO 3) 2 , PbSO 4 and PbCO 3 on MCCX catalyst varied. The PbSO 4 had the most serious poisoning on MCCX catalyst, while PbCO 3 had poisoning effect on catalysts even at 300 °C. Lead species poisoning had bad impact on the structure of zeolite X on MCCX catalyst, and caused some agglutination of Cu species. Likewise, the Pb species might primarily occupy the active site of Mn and Cu species and influence the redox property of catalysts, thereby obstructing the redox and oxidation cycles on catalysts surface. In addition, the PbCl 2 and PbNO 3 species predominantly affected the Brønsted acid sites and occupied the Cu or Mn active sites, inhabiting the absorption and conversion of nitrites and nitrates on the catalyst surface. Moreover, PbSO 4 and PbCO 3 species mainly impacted the adsorption of NO + O 2 and the conversion of nitrites and nitrates on the catalysts. [ABSTRACT FROM AUTHOR]