Unraveling the morphology and crystal plane dependence of bifunctional MnO2 catalyst for simultaneous removal of NO and CO at low temperature

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 MnO2 (& alpha;-, & beta;-, & gamma;-, and & delta;-) 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 & gamma;-MnO2 catalyst exhibited the best catalytic activity, achieving 90% NO removal efficiency and 82% CO conversion rate at 175 degrees C. Reaction kinetics confirmed that & gamma;-MnO2 catalyst exhibited a lower Ea for both NO reduction and CO oxidation compared to & alpha;-MnO2, & beta;-MnO2 and & delta;-MnO2 catalysts. Meanwhile, the interaction of between NH3-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 & gamma;-MnO2 catalyst in the NH3-SCR reaction. The results of NO + O2-TPD and in situ DRIFTS experiments revealed that CO contributed to the adsorption and oxidation of NO, thus promoting the L-H pathway over & gamma;-MnO2 catalyst. Finally, a possible mechanism model for simultaneous removal of NO and CO over & gamma;-MnO2 catalyst was proposed.

Automated summary

Four different crystalline phases of MnO2 catalysts were synthesized, and their effects on the catalytic performance for NO reduction and CO oxidation were investigated. It was found that the γ-MnO2 catalyst exhibited the best activity, achieving high NO removal efficiency and CO conversion rate. The presence of CO was found to enhance the catalytic activity of the γ-MnO2 catalyst in the NH3-SCR reaction.