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

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/NO_x程序升温脱附和NH₃/NO_x吸附红外光谱等手段对催化剂进行了表征. MnO_x-CeO₂催化剂表现出良好的低温（100-150 ℃）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 ℃）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.

Tailored temperature window of MnOx-CeO2 SCR catalyst by addition of acidic metal oxides

A MnO_x-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 NO_x 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/NO_x temperature-programmed desorption analyses, and infrared spectroscopic measurements of NH₃/NO_x adsorption. The MnO_x-CeO₂ catalyst exhibited the greatest low-temperature (100-150 ℃) 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 ℃) was suppressed, and the adsorption of NH₃ on Brönsted and Lewis acid sites was strengthened. Consequently, the temperature window of SCR reaction shifted to higher temperatures in the order Nb₂O₅< WO₃< MoO₃.