酸性金属氧化物对锰铈氧化物催化剂脱硝温度窗口的调控作用(英文)

Tailored temperature window of MnO_x-CeO_2 SCR catalyst by addition of acidic metal oxides

利用溶胶-凝胶法,采用三种酸性金属氧化物(氧化铌、氧化钨和氧化钼)对锰铈复合氧化物催化剂进行了改性.测试了催化剂的氮氧化物选择性催化还原(SCR)活性,以筛选对应不同温度窗口的合适酸性氧化物改性剂.同时评价了催化剂的NO氧化和NH3氧化活性.利用X射线衍射、BET比表面积测试、H2程序升温还原、NH3/NOx程序升温脱附和NH3/NOx吸附红外光谱等手段对催化剂进行了表征.MnOx-CeO2催化剂表现出良好的低温(100-150°C)活性.酸性金属氧化物的添加削弱了催化剂的氧化还原特性,从而抑制了NH3的活化和NO2辅助的快速SCR反应.与此同时,相对高温(250-350°C)区NH3的氧化也受到了抑制,B酸和L酸上的NH3吸附得以增强.因此,催化剂的SCR脱硝温度窗口向高温移动,改性效果Nb2O5<WO3<MoO3.

A MnOx‐CeO2 catalyst was modified with various acidic metal oxides（Nb2O5, WO3, and MoO3） using a sol‐gel method. The activities of the obtained catalysts were measured for the selective catalytic reduction（SCR） of NOx with NH3 to screen suitable acidic metal oxides for different temperature windows. The catalytic activities for NO and NH3 oxidation were also evaluated. The catalysts were characterized by X‐ray diffraction, N2 adsorption, H2 temperature‐programmed reduction, NH3/NOx temperature‐programmed desorption analyses, and infrared spectroscopic measurements of NH3/NOx adsorption. The MnOx‐CeO2 catalyst exhibited the greatest low‐temperature（100–150 C） activity. The addition of acidic metal oxides weakened the redox properties of the catalyst, resulting in inhibition of the partial oxidation of the adsorbed NH3 and NO2‐assisted fast SCR reactions. Meanwhile, the oxidation of NH3 at relatively high temperatures（250–350 C） was suppressed, and the adsorption of NH3 on Bronsted and Lewis acid sites was strengthened. Consequently, the tem‐perature window of SCR reaction shifted to higher temperatures in the order Nb2O5 WO3 MoO3.