过渡金属类质同象置换对铁基尖晶石NH3-SCR反应性能的调控

Because of the isomorphous substitution of iron by transition metal, iron ore with the spinel structure has lower Fe content and its smelting cost is higher. Therefore, a more rational way should be developed to comprehensively use iron ore with the spinel structure. Furthermore, some problems still exist although V2O5-WO3/TiO2 has been widely employed as a SCR catalyst to control the emission of NOx from coal-fired power plants for several decades. Therefore, a few researchers have focused on the exploitation of new kinds of SCR catalysts to substitute the conventional vanadium based catalyst. In this proposal, Fe based spinel is developed as an environmental-friendly and low cost catalyst for the control of NOx emission from coal-fired power plants. Both the effect of the isomorphous substitution of iron by transition metal on the physicochemical properties of Fe based spinel and the mechanism of NH3-SCR reaction over Fe based spinel will be firstly investigated. Then, the structure-activity relationship among the isomorphous substitution of iron by transition metal, the physicochemical properties of Fe based spinel and its performance for NH3-SCR reaction will be built. Based on the structure-activity relationship, Fe based spinel with an excellent NH3-SCR performance will be devised with the selective isomorphous substitution of iron by transition metal. Furthermore, natural Fe based spinel will be modified to improve its NH3-SCR performance according to the structure-activity relationship and the results of mineral spectra study. In conclusion, this proposal not only develops a new view for the design of new kinds of NH3-SCR catalysts to control NOx emission from coal-fired power plants but also proposes a more rational way for the comprehensive utilization of natural Fe based spinel, which will help the development of environmental mineralogy.

尖晶石型铁矿石由于过渡金属类质同象置换，品位较低，冶炼成本较高，亟需拓展资源综合利用的途径。与此同时，用于控制燃煤电厂氮氧化物排放的商业SCR催化剂仍存在较大不足，亟需开发新型催化剂替代品。本课题创新性地将铁基尖晶石引入燃煤电厂SCR催化剂研究，拟深入研究过渡金属类质同象置换对铁基尖晶石物化性质的影响和铁基尖晶石SCR反应的微观机制，建立过渡金属类质同象置换、铁基尖晶石物化性质及其SCR反应性能三者之间的构效关系。依据建立的构效关系，一方面有目的地利用过渡金属类质同象置换对铁基尖晶石进行化学裁剪，设计出具有优异SCR反应性能的铁基尖晶石；另一方面，结合天然铁基尖晶石矿物谱学研究，对天然铁基尖晶石进行改性，提高其SCR反应性能。本课题的开展不仅能够拓展天然铁基尖晶石资源综合利用途径，也将为燃煤电厂SCR催化剂的研发提供了一个全新的研究思路，将有力推动环境矿物学的发展，具有显著的科学意义。

氮氧化物是形成灰霾和光化学烟雾的主要前驱体之一，控制燃煤烟气氮氧化物排放是近年来我国大气污染防治工作的重中之重。目前燃煤电厂所采用的氮氧化物控制技术主要为氨气选择性催化还原技术（NH3-SCR），所用的催化剂为V2O5-WO3/TiO2。但它存在低温活性差、高温N2选择性差、有毒和复杂烟气条件下适应能力差等缺点。如何定向设计出价格低廉、环境友好、复杂烟气条件下适应性强的NH3-SCR催化剂就成为氮氧化物控制技术研究中的一个科学难点。我们创新性地将铁基尖晶石引入NH3-SCR反应研究，基于NH3-SCR反应的微观机制研究，校正了NH3-SCR反应的动力学模型，建立了过渡金属类质同像置换、铁基尖晶石物理化学性质及其NH3-SCR反应性能三者之间的构效关系。在此基础上，依据建立的构效关系，成功利用过渡金属类质同像置换等手段成功调控了铁基尖晶石NH3-SCR反应的温度窗口、反应活性和选择性。.尖晶石NH3-SCR反应机制研究显示其反应活性和选择性与矿物表面酸性位的强度和数量以及活化吸附NH3的活性位的氧化性等因素有关。我们通过Ti4+类质同像置换提高了尖晶石在300-400 oC的活性，用Mn4+类质同像置换提高了尖晶石在低温段（100-200 oC）的活性。我们利用钒钛磁赤铁矿结构中V5+和Fe2+离子间的快速电子交换，将其引入NH3-SCR反应研究，即保持了优异的反应活性，又抑制了温室气体N2O的生成。我们还将钛磁赤铁矿表面硫酸化，使其表面NH3的吸附位和活化位分离，拓宽了其在高温段NH3-SCR反应的温度窗口，使其适用于褐煤燃烧的烟气。我们还在锰磁赤铁矿界面发现N2O生成速率与气态NO浓度无关，这对抑制低温NH3-SCR反应中N2O的形成具有非常重要的意义。在此基础上，我们将MnOx负载在钛磁赤铁矿的表面，即获得了较好的低温NH3-SCR活性，又保持了优异的N2选择性。