单斜相纳米氧化锆基低温SCR催化剂脱硝机制研究

Denitration Mechanism of Monoclinic-phase Nano Zirconium Oxide-based Catalysts

以纳米m-ZrO2为载体,用浸渍法制备出MnOx-CeO2/m-ZrO2催化剂,考察反应温度、活性组分负载量对催化剂NH3-SCR脱硝活性影响,探讨催化剂表面织构特征,分析催化剂脱硝活性机制.结果表明,在低温脱硝温度范围,提高反应温度、增加活性组分负载量,有利于催化剂脱硝效率的增加.110℃时,2.5%MnOx-CeO2/m-ZrO2脱硝效率为55.5%,15%MnOxCeO2/m-ZrO2脱硝效率达93.5%.XRD、BET、XPS、H2-TPR表征结果表明,催化剂表面具有良好的氧化还原能力,表面织构对脱硝反应有利.NH3-TPD测试显示,MnOx-CeO2/m-ZrO2催化剂的脱硝反应机制为:NH3吸附在催化剂表面的Lewis酸性位和Brnsted酸性位上,通过反应生成相应中间产物NH2NO或NH4NO2,中间产物进一步分解最终转变为N2和H2O;催化剂总脱硝反应效率中,在Lewis酸性位上的脱硝反应占比较大.

The MnOx-CeO2/m-ZrO2 catalyst was prepared by impregnation with nano monoclinic-phase zirconium(m-ZrO2) as the supporter. The influence of active component and reaction temperature on the denitration performance of the catalyst was investigated,while the surface properties of the catalyst and the denitration mechanism were discussed. The denitration efficiency was improved as the active component increased and the reaction temperature rose. The denitration efficiency of 2. 5% MnOx-CeO2/ m-ZrO2 catalyst at110℃ was 55. 5% while that of 15% MnOx-CeO2/ m-ZrO2 catalyst was 93. 5%. The results of XRD,SEM,BET and H2-TPR showed that the surface structure of the loaded catalyst was beneficial for denitration and oxidation-reduction. NH3-TPD test demonstrated that NH3 was adsorbed at the Lewis acid sites and Brnsted acid sites on the surface of catalysts. Intermediate products NH2NO and NH4NO were generated from a series of reactions between NO and NH3 and finally transformed into N2 and H2O. Most of the denitration process happened at Lewis acid sites.