改性稀土精矿低温NH3-SCR脱硝的协同作用机理研究

Rare earth metal oxides are the research hotspots of low temperature NH3-SCR denitration catalysts. A large number of studies have shown that cerium-based polymetallic oxide have good low temperature SCR catalytic performance and it is the ideal catalyst active components. Based on the characteristics of high content of Ce and low content of active metal oxides，rare earth ore were subjected to multi-atmosphere roasting and loaded with iron-manganese metal oxide to obtain a new low-temperature Ce-based SCR denitration catalyst. The effects of the mass ratio of rare earth ore/ferromanganese oxide and calcination conditions on the microstructure，surface properties and catalytic denitrification activity of the new catalysts will be studied by using a variety of in situ and off-site test methods. The changes of valence and the electron transfer path of catalyst activity components during SCR reaction will be revealed. The multi-step catalytic process of NH3-reduced NOx on the surface of new catalyst and the synergistic effect between active components such as Fe，Mn and Ce will be elucidated. The results will provide a basis for exploring the mechanism of low temperature SCR reaction to guide the modification of the Baiyunbao Rare earth ore.

稀土金属氧化物是目前低温NH3-SCR脱硝催化剂的研究热点。已有结果表明Ce基多金属氧化物具有良好的低温SCR催化性能，是理想的催化剂活性组分。本项目基于白云鄂博稀土精矿Ce、La等稀土元素含量高、活性过渡金属氧化物含量低的特点，通过多气氛焙烧对其进行除杂并负载铁锰金属氧化物制备新型Ce基低温SCR催化剂，采用多种原位和离位表征手段，重点研究稀土精矿/铁锰氧化物负载量和焙烧条件对新型催化剂微观结构、表面性质、低温催化活性的影响；SCR反应过程中催化剂活性位价态变化及电子转移路径；阐明新型催化剂表面NH3还原NOx的多步催化过程及Fe、Mn、Ce等活性组分之间的协同作用，为探究低温SCR反应机理从而指导稀土精矿的改性提供依据。

稀土多金属氧化物具有优异的低温NH3-SCR脱硝催化性能而受到越来越多研究者的关注。由于白云鄂博稀土精矿Ce、La等稀土元素含量高，经酸碱改性、负载过渡金属等手段制备的稀土矿物催化剂具有优良的脱硝性能，实验表明其低温活性最高可达92%甚至更高。负载Mn氧化物稀土精矿表面氧化还原能力增强，NH3吸附性能增强。Ce以Ce3+和Ce4+的形式共存。Mn以Mn3+和Mn4+的形式共存。铈和锰的协同作用提高了催化活性。负载Fe氧化物铁元素的增加有利于催化剂的脱硝性能。CeO2的结构发生扭曲，形成Ce-Fe固溶体，催化剂中暴露出更多的氧空位。NO在Ce3+和Fe2+的作用下生成活化硝酸盐，并与酰胺反应生成N2和H2O。Fe和Mn的引入增加了催化剂表面的酸性位点和酸的量，导致催化剂表面形成了大量的氧空位，出现了更多的氧，有利于氧的迁移。采用傅里叶变换红外光谱(FTIR)对新型催化剂进行了表征，表征了活性物质在催化剂表面的吸附和转化行为，并探讨了反应机理。结果表明，整个反应过程遵循L-H机制，气态NO在催化剂表面吸附活化生成双酯硝酸盐，桥接硝酸盐和NH3/NH4+为主要参与反应的中间产物，两者在催化剂表面发生氧化还原反应生成N2和H2O。上述结果表明，CeCO3F-独居石载体具有优良的性能，为稀土精矿的高价值利用提供了理论依据。