过渡金属氧化物-金属有机骨架复合低温脱硝催化剂的制备及其抗水抗硫性能研究

The traditional catalysts employed in the removal of NOx from flue gas are easily poisoned by the high concentration of dust and sintered due to the high temperature of the flue gas. Hence, many efforts are devoted to develop the low-temperature NH3-SCR denitration catalysts. However, the current promising low-temperature catalysts that usually contain transitional metal oxides or zeolites as active components usually suffer from the poor tolerance to H2O and SO2, which thus severely constrains the development of low-temperature denitration technology. Our work here is based on the strategy of introducing Metal Organic Frameworks (MOFs), a novel ordered nanoporous material, to the metal oxides catalysts. With the shape selectivity of MOFs, diffusion of SO2 and H2O can be inhibited and the active components are hence effectively protected. The contents in this proposal include following sections. Firstly, manganese oxides with doped transition metal oxides will be loaded onto TiO2 nanorod arrays to prepare composite catalyst (M-MnOx/TiO2). The corresponding mechanisms of the low-temperature NH3-SCR reactions will be studied as well to regulate distribution of active sites. Then, both theoretical analysis and experimental research will be conducted to select the ideal MOFs. Meanwhile, synthesis of MOFs on the M-MnOx/TiO2 catalysts to generate coating membrane will be investigated and the low-temperature NH3-SCR reaction mechanisms of as-obtained composite catalysts will be systematically discussed. Finally, a further optimization to the preparation process is designed according to the result of the mechanism analysis. This proposal focuses on the preparation of the novel low-temperature denitration catalysts with enhanced tolerance to SO2 and H2O poisoning. It will provide both theoretical instruction and experimental data to the research on the low-temperature denitration technology, and explore the application of ordered porous materials onto the NH3-SCR research.

传统烟气脱硝过程的高温高尘环境使得催化剂易因烧结、中毒而失活，开展低温脱硝催化剂的研制具有重要意义。现有过渡金属氧化物及沸石催化剂均面临低温下抗水抗硫性能不佳等问题，制约着低温脱硝技术的发展。本项目拟将金属有机骨架（MOFs）这类有序多孔材料引入至低温脱硝催化剂进行结构设计，利用孔道择形效应阻隔SO2与H2O，提高催化剂抗水抗硫能力。项目拟首先制备具有高脱硝活性的掺杂型锰金属氧化物/TiO2纳米棒阵列催化剂，并研究活性组分的调变对于催化剂低温脱硝及抗水抗硫性能的影响。在此基础上，结合理论分析与实验结果筛选不利于SO2与H2O吸附的MOFs保护层材料，同时探索在过渡金属氧化物表面包覆MOFs的方法，制备出抗水抗硫型高效复合低温脱硝催化剂。本项目旨在揭示MOFs保护机制下低温脱硝催化剂的制备与抗水抗硫机理，拓展有序多孔材料在脱硝领域的应用，为低温脱硝技术的推广提供有价值的理论和实验依据。

低温烟气脱硝技术能够实现催化剂在烟道系统中的后置，进而有效延长催化剂的使用寿命，具有良好的应用前景。其中，催化剂作为此项技术的核心，也就成为了研究的重点。低温脱硝催化剂的构建通常基于多种过渡金属氧化物的有机耦合。然而，在低温（100~250℃）条件下，烟气中的SO2和H2O会导致金属氧化物中毒，降低脱硝效率。为了解决上述问题，本课题以过渡金属氧化物为内核，引入金属有机骨架材料（MOFs）作为壳层，构建了包覆型烟气脱硝催化剂，开发了一种具有良好应用前景的低温烟气脱硝催化剂。首先，探究了MnOx与稀土元素之间的作用机制，发现仅需较低比例的CeOx与MnOx（1:10）进行掺杂，即可获得90%以上的脱硝效率。结合X光电子能谱、H2-程序升温还原等手段探究其反应机理，可以认为CeOx的掺杂能够提高Mn4+的比例。基于原位漫反射傅里叶红外光谱分析，发现反应路径发生于吸附态的NH3和吸附态的NOx物种之间，遵循Langmuir-Hinshelwood机理（L-H机理）。进而，我们选定课题研究围绕MnOx与CeOx作为主要活性组分。在筛选MOFs的种类过程中，我们发现，ZnO纳米棒阵列与MnOx之间具有良好的协同作用，相比于TiO2纳米棒阵列，ZnO能够有效增加催化剂表面酸性位点数量。借助表面化学吸附氧（Oβ）含量增加这一优势，MnOx-ZnO纳米棒阵列复合脱硝催化剂的氧化还原能力得到提高，在150-250℃范围内，脱硝效率均在80%以上,反应过程同样遵循L-H机理。结合实验与理论分析，选定以Zn2+为金属位点的ZIF-8作为壳层，充分利用其制备过程简单、稳定性优异、孔结构适宜等特性。以此为基础，我们以ZnO纳米棒为牺牲模板，采用晶种铺设-水热生长-壳层原位包覆的方法，成功制备了MnOx-ZnO@ZIF-8的核壳结构催化剂。本课题所获得的烟气脱硝催化剂结构稳定、脱硝性能良好，为制备高效率低温烟气脱硝催化剂提供了重要的理论和实验依据，对本项技术的进步具有重要参考价值。