Catalytic oxidation of NO over MnOx–CoOx/TiO2 in the presence of a low ratio of O3/NO: activity and mechanism

Abstract

In order to broaden the temperature range of NO oxidation reaction in flue gas and maintain high oxidation efficiency, various loading amounts of MnO_x–CoO_x/TiO₂ mesoporous catalysts were tested in the catalytic oxidation of NO. It was found that 15%MnO_x–CoO_x(2 : 1)/TiO₂ demonstrated the best adsorption performance to oxygen species and contained more oxygen vacancies, as well as the best surface oxygen mobility, thus exhibiting excellent NO catalytic oxidation activity. O₃ (O₃/NO < 1) combined with 15%MnO_x–CoO_x(2 : 1)/TiO₂ improved the oxidation efficiency of NO at 50–400 °C, especially below 250 °C. When the temperatures were less than 250 °C, the oxidation efficiencies of NO by O₃ over 15%MnO_x–CoO_x(2 : 1)/TiO₂ were 5–13% higher than the calculated theoretical efficiencies. This indicated that there was a synergistic effect between O₃ and 15%MnO_x–CoO_x(2 : 1)/TiO₂ below 250 °C. Based on the results of in situ DRIFTS studies, it was deduced that monodentate nitrates were the main intermediates that produced a synergistic effect due to the introduction of O₃. In addition, O₃ accelerated the transformation between nitrate species, decreased the decomposition temperature of nitrate species, and inhibited the accumulation of nitrate ions, thus improving the oxidation efficiency of NO.