Catalytic oxidation of NO over MnO(x)–CoO(x)/TiO(2) in the presence of a low ratio of O(3)/NO: activity and mechanism

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)/TiO(2) mesoporous catalysts were tested in the catalytic oxidation of NO. It was found that 15%MnO(x)–CoO(x)(2 : 1)/TiO(2) 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. O(3) (O(3)/NO < 1) combined with 15%MnO(x)–CoO(x)(2 : 1)/TiO(2) 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 O(3) over 15%MnO(x)–CoO(x)(2 : 1)/TiO(2) were 5–13% higher than the calculated theoretical efficiencies. This indicated that there was a synergistic effect between O(3) and 15%MnO(x)–CoO(x)(2 : 1)/TiO(2) 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 O(3). In addition, O(3) 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.