WO3/TiO2-ZrO2脱硝催化剂制备及其NH3活化机理

Preparation of WO_3/TiO_2-ZrO_2 catalyst for selective catalytic reduction and mechanism of NH_3 activation

采用共沉淀法制备了WO3/TiO2-ZrO2脱硝催化剂,并用固定床反应器进行活性评价,采用BET、XRD、TPD、氨气吸附漫反射FT-IR进行表征。结果显示,ZrO2掺杂增强了TiO2的Lewis酸性;负载WO3之后,位于3.1~1.7nm之间孔隙的稳定性显著增强;NH3的吸附与活化分别由TiO2-ZrO2载体和WO3完成;WO3中W元素强大的电负性,促进了NH3的N—H键由共价键向离子键过渡,进而导致了NH3的活化。脱硝活性结果显示：当WO3含量为9%（质量）时,催化剂脱硝活性最高,并在320~420℃的温度窗口保持94%以上。（9%）WO3/TiO2-ZrO2具有更加稳定的孔隙结构（4.4~1.7nm）,表面Br？nsted酸中心数量增加,Lewis酸中心的强度和酸量增加的幅度最大,NH3-SCR过程中的活性中间产物NH2的吸收峰更加明显,这些特征可能是其脱硝活性最好的原因。

（x）WO3/TiO2-ZrO2 catalysts with different WO3 content were prepared by the impregnation method and the catalytic performance for the selective catalytic reduction of NOx with NH3（NH3-SCR） was investigated in a fixed-bed stainless steel reactor. The catalysts were characterized by BET, XRD, NH3-TPD andin situ DRIFTS analysis of NH3 adsorption, and revealed the change of the structural property and acidic capacity. The characterization results showed that WO3 was in a well-dispersed state and WO3addition enhanced the thermal stability of catalysts obviously. The adsorption and activation of NH3 were caused by TiO2-ZrO2and WO3, respectively. It was found that W displayed a huge electronegativity and prompted the transfer of the N—H bond of NH3 from covalent bond to ionic bond, which could incur theNH3activation. The results of catalytic activity indicated that the catalyst with 9%（mass） WO3 content exhibited 94% NO conversion within the wide temperature range of 320℃ to 420℃. （9%）WO3/TiO2-ZrO2possessed comparatively higher intensity of Lewis acidity and larger amount of Bronsted acidity as well as more stable pore structure （4.4—1.7 nm）. Besides, the absorption peak of the active intermediate species NH2was more obvious. All these characters probably accounted for its better catalytic performance.