SO2增强α-Fe2O3/H2O2蒸汽氧化燃煤烟气NO的反应机制研究

It is a significant action to develop the low-temperature denitrification technology of coal-fired flue gas for the sustainable development of national industry. The project aims to oxidize nitric oxide (NO) with hydroxyl radicals from the activation of hydrogen peroxide (H2O2) vapor over α-iron oxide (α-Fe2O3) catalyst so that the flue gas denitrification can be achieved. In the NO oxidation with the catalytic decomposition of H2O2 vapor over α-Fe2O3, the acidic and reductive SO2 performs an enhancement effect on the NO oxidation efficiencies. However, there are still huge challenges in clarifying the enhancement mechanism. With respect to those questions, the surface structure characterization, denitrification experiments, free radical scavenging experiments and catalytic kinetic studies with in situ sulfated α-Fe2O3 will be carried out in this project. The correlations between the surface acidity, electronic state, surface defects of catalysts and NO removal efficiencies will be evaluated. The acid-catalyzed mechanism of H2O2 activation over the in situ sulfated α-Fe2O3 is elucidated. In addition, the reaction path of SO2-enhanced NO oxidation with the H2O2 activated by sulfated α-Fe2O3 will be analyzed and consequently, the reduction mechanism of SO2 will be illuminated. This study focuses on the mechanism of SO2-enhanced NO oxidation with catalytic decomposition H2O2 vapor over α-Fe2O3, and meanwhile provides a theoretical guidance for the development of novel low-temperature denitrification technology.

研发燃煤烟气低温脱硝技术是实现我国工业绿色发展的重要举措。本项目致力于以α-氧化铁（α-Fe2O3）催化剂活化过氧化氢（H2O2）蒸汽产生羟基自由基，进一步氧化一氧化氮（NO），实现燃煤烟气脱硝。在α-Fe2O3活化H2O2蒸汽氧化NO的过程中，烟气中具有酸性和还原性的SO2会增强NO氧化效率，厘清强化机制仍然存在巨大挑战。本项目以原位硫酸化α-Fe2O3为催化剂，采用表面结构表征、脱硝实验、自由基清除实验和催化机理动力学的方法，研究表面结构与NO氧化的相关性，确定SO2对H2O2蒸汽活化的酸催化机制；进而解析SO2存在时的NO氧化反应路径，阐明SO2对H2O2蒸汽活化的还原机制。本研究聚焦烟气中SO2对α-Fe2O3活化H2O2蒸汽氧化NO的强化机制，为研发燃煤烟气低温脱硝工艺提供科学指导。

研发低温工业废气中氮氧化物减排技术是大气污染治理领域的重要方向之一，也是“十四五”工作计划中关于细颗粒物和臭氧协同控制、基本消除重污染天气的重要方向。本项目围绕SO2增强α-Fe2O3活化H2O2脱除低温烟气NO的机理开展，开展性能测试、结构表征、动力学模拟等实验，以解释增强反应性能的关键结构和限速步骤。重要结果及关键数据阐述如下：（1）开展SO2对不同H2O2活化手段脱硝的影响规律研究。以SiO2为活化介质的热活化H2O2蒸汽脱硝研究，当反应温度为400℃，H2O2/NO摩尔比为3.10时，脱硝效率69%（0 ppm SO2）提升至91%（2000 ppm SO2）。进而，开展Fe2O3/SiO2活化H2O2的低温脱硝实验，当反应温度为140℃，H2O2/NO摩尔比为3.10时，Fe2O3/SiO2活化H2O2脱硝效率31%（0 ppm SO2）提升至95%（2000 ppm SO2），证明对于热活化H2O2脱硝或是Fe2O3/SiO2活化H2O2脱硝，SO2均起到明显的增强作用，且对Fe2O3/SiO2活化H2O2脱硝反应体系的增强作用更显著。SEM-EDS、UV-Vis DRS、XPS等表征分析以及自由基清除实验结果表明SO2在催化剂表面氧化成H2SO4，进而H2SO4在H2O2活化产生•OH反应路径中表现为改变中间活性物种的作用。（2）“预处理-脱硝”分步实验和SO2饱和滴定实验结果表明SO2在催化剂表面快速吸附氧化，得到的H2SO4是促进脱硝性能的关键，H2O2和NO的氧化产物，如NO2和HNO3，能将SO2氧化成H2SO4，从而加速H2O2活化产生•OH。然而，同时研究也发现，SO2的还原性对Fe2O3活化H2O2氧化NO反应起抑制作用。（3）开展预硫酸化Fe2O3/SiO2活化H2O2氧化NO反应动力学研究。分别假设反应步骤和脱附步骤为反应的限速步骤，基于最优拟合结果推测H2SO4的强酸性作用会加速H2O2分解产生•OH，使得反应决速步骤表现为NO氧化中间物种的再氧化反应成为NO氧化反应的控速步骤。综上，申请人围绕SO2对H2O2在α-Fe2O3表面活化形成•OH氧化NO的增强机制进行了细致、深入的探索，研究成果为研发新型低温抗硫脱硝工艺奠定了一定的理论基础。