Catalytic performance of MnO_x/WO_3/TiO_2 catalyst for low-temperature selective catalytic reduction of NO_x by NH_3

Series of MnOx/WO3/TiO2with different WO3contents were prepared by a one-step impregnation method and their catalytic performance for the low-temperature selective catalytic reduction of NOx with NH3(NH3-SCR) was investigated under the condition of simulated composition of flue gas.Three conditions for macro-transient experiments were designed to study the role of components in the smog on the process of catalytic reaction in order to figure out the process of the catalytic reduction of NOx.It is found that the addition of appropriate amount of WO3 can improve remarkably the catalytic activity of Mn-based catalysts.Particularly,the 15%MnOx/5%WO3/TiO2 exhibited better low-temperature catalytic performance with above 85% NO conversion in the wide temperature range of 80 240 ℃.However,higher and lower WO3 contents can reduce the catalytic activities of the tertiary oxides,though the catalyst with 7.5% WO3 content has better high-temperature activity(240 ℃).Macro-transient experiments reveal that the absorption and activation of NH3is of the utmost importance in the NH3-SCR reaction.Gaseous NH3 in the presence of O2 can reduce NOx slightly and O2 can stimulate the oxidization of NOxand protect the active center on the surface of catalysts so as to promote the absorption and activation of NH3.