改性铁基催化剂低温SCR脱硝性能优化机理

Compared with pratical vandia-titanate mixed metal oxide catalysis, iron-based catalyst has some advantages such as non-toxicity, good ati-H2O and SO2 poisoning, low cost of denitration and so on. Therefore, iron-based catalyst used to reduce nitrogen oxides produced from the power plant becomes the research focus.Among the iron metal oxides,γ-Fe2O3 catalyst shows the best low-temperature NH3-SCR activity, and is the great potential active component of the catalyst for low-temperature NH3-SCR. In this research project, microwave is introduced to prepareγ-Fe2O3 iron-based catalysts, and some transition metal oxides or/and rare earth metal oxides are also added into γ-Fe2O3 iron-based catalysts so as to improve its low-temperature NH3-SCR activity. At the some time, the optizimation mechanism of microwave and the additives in NH3-SCR overγ-Fe2O3 iron-based catalysts will be discussed. The effect of structural parameters and operation parameters on the low-temperature SCR activity of γ-Fe2O3 iron-based catalysts will be investigated in detail, and then the reaction kinetics model for selective catalytic reduction of NO over γ-Fe2O3 iron-based catalysts is set up so as to reveal the interal relations between SCR activity and those parameters. The adsorption/desorption capacity of NO and NH3 over γ-Fe2O3 iron-based catalysts is also investigated to study its surface acid by temperature programed desorption methods(TPD)，and the intermediate material will be also studied so as to study the NH3-SCR mechanism over γ-Fe2O3 iron-based catalysts by diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS). Finally, the optimization mechanism how microwave and different additives improve the low-temperature SCR activity of γ-Fe2O3 iron-based catalysts will be put forward. The characterizations of catalysts will be measured by BET, XRD, XPS and so on, and the characteristic results will be used to study the law how microwave parameters, the kinds and the additive amount of transition metal oxides or/and rare earth metal oxides influence the microstructure of γ-Fe2O3 iron-based catalysts so as to reveal the synergistic effect between the active component and the additive, or the synergistic effect during various additives. his research results will promote and develop the theoretical foundation of the low-temperature iron-based catalysts used to control the emission of nitrogen oxides produced during the coal burning from the power plant.

与实用钒钛催化剂相比，铁基催化剂具有无毒、抗H2O和SO2毒化能力强、脱硝成本低廉等优点，成为火电站SCR脱硝的研究热点。在铁氧化物中，γ-Fe2O3催化剂低温脱硝性能良好，是极具潜质的低温催化剂活性组分。本研究把微波引入催化剂制备过程，并添加过渡金属、稀土金属助剂对γ-Fe2O3铁基催化剂进行低温改性，揭示其优化脱硝反应机理。分析结构参数和运行参数对催化剂低温SCR脱硝性能的影响规律，建立其催化脱硝反应动力学模型，确定其脱硝性能与各参数间的内在联系；考察其NO和NH3脱附特性，以及瞬态反应表面吸附中间产物，确定其SCR脱硝反应机理，揭示微波，过渡金属、稀土助剂优化其低温脱硝性能的主要机理；通过对催化剂表征分析，研究微波参数，过渡金属、稀土种类、添加量等对其微观结构特性的作用规律，探讨活性组分与单/多助剂元素的协同作用机制。此研究将充实铁基低温SCR催化剂用于火电厂脱除NOx的理论基础。

来源广泛、成本低廉且环境友好的铁基催化剂是一种优良的钒系催化剂替代产品，Synth-Maghemite（γ-Fe2O3）为铁氧化物的一种主要存在形式，开发潜力巨大，本项目主要围绕该形式的铁氧化物开展，所得主要研究进展及成果如下：.沉淀-微波热解法可实现Synth-Maghemite催化剂的简易制备，所得催化剂最高脱硝效率达到96%；其活性组分γ-Fe2O3成分单一、纯度较高，2～10 nm孔径区间均匀分布狭缝形介孔，同时在100～50000 nm区间含有丰富的大孔，催化剂表面晶格氧丰富、热稳定性高，抗SO2、抗H2O中毒性能优良。NH4OH沉淀剂、FPM方法、400℃空气气氛煅烧为最佳制备参数，α-Fe2O3的生成对SCR反应不利；以NH4OH为沉淀剂，利用共沉淀法掺杂铈氧化物能够提高铁氧化物的中低温SCR脱硝性能；氨基沉淀剂会抑制前驱体中α-FeOOH和α-Fe2O3的形成，促使铁、铈组分在铁铈复合氧化物催化剂中形成固溶体；Ti掺杂改性Synth-Maghemite催化剂最高脱硝效率达到98.3%且活性温度窗口大幅拓宽；铁铈复合氧化物催化剂表面形成高活性的吸附氧和晶格氧；掺杂铈氧化物会促使铁氧化物表面形成更多Lewis酸位；与W、Mo和Zr相比，掺杂Ti能够明显提高Fe0.95Ce0.05Oz催化剂的低温SCR脱硝性能，促使其脱硝温度窗口向低温偏移；微波水热处理会加速铁铈钛复合氧化物催化剂前驱体的晶化速率；Synth-Maghemite催化剂SCR反应中同时存在E-R机理和L-H机理2种反应路径，L-H机理路径的存在使催化剂活化能大幅降低；Ti掺杂Synth-Maghemite催化剂能够大幅提高其表面Lewis酸性位和Brönsted酸性位数量，表面Fe主要以Fe3+形式存在，Ti主要以Ti4+形式存在；SCR反应过程中NH3吸附主要发生在Fe3+位点，吸附后主要以伯胺（-NH2）、离子态NH4+和吸附活化态NH3形式参与反应。