TiO2负载α-Fe2O3量子点解耦催化尿素脱硝/汞氧化复合过程机理研究

The key issue to achieve the clean combustion of coal is the removal of nitric oxides (NOx) and mercury (Hg), and simultaneously realizing the NOx reduction and the Hg0 oxidation by special catalysts is an important method to remove NOx and Hg. Nowadays, more and more coal-fired power plants have adopted urea, which is famous for its nontoxic, harmless, and high security during use, as the denitration reducer. However, little research has been done on the application development and the initial function mechanism of the special catalysts for urea-basis nitric oxides and mercury removal. In this project,catalysts are prepared by loading α-Fe2O3 quantum dots on TiO2 carriers to increase the number of active sites, and electrons on catalysts surface are controlled to incease the activity. The catalytic effect on urea decomposition, isocyanic acid hydrolysis, NOx reduction, and Hg0 oxidation independence processes and their coupling process is studied by decoupling-coupling experiments, to make clear the the effect of vital factors in sturcture regulations. The kinetic model of α-Fe2O3/TiO2 catalyzing urea denitration and mercury oxidation is established according to the Density Functional Theory and the First Principle, aiming to reveal the initial mechanism of gas-solid reactions in the urea-NOx-Hg0-active species-outside atmosphere multicomponent system. The research results will significantly contribute to the clean combustion of coal.

燃煤烟气中氮氧化物（NOx）与汞（Hg）的脱除是实现煤清洁燃烧亟需解决的关键问题，采用特制催化剂同时催化还原NOx和氧化Hg0是实现联合脱硝脱汞的重要技术手段。虽然尿素以无毒无害的高安全性成为日益广泛应用的脱硝还原剂，但当前尚无专门针对尿素脱硝脱汞复合过程催化剂的基础研发及其作用机制的研究。本项目将α-Fe2O3量子点构筑于高比表面积TiO2载体之上以提升单位质量催化剂表界面活性位点数量，调控表界面电子云空间构型进而强化单位活性位点催化活性；通过解耦-耦合催化实验研究催化剂对尿素分解/异氰酸水解/NOx还原/Hg0氧化独立及复合过程的催化效能，明晰跨尺度结构调控关键变量的作用规律；依据密度泛函理论及第一性原理阐释尿素-NOx-Hg0-活性物种-外场环境多元体系气-固反应动力学机制，实现接近真实催化反应条件下原子水平的理论模拟。本项目成果对实现煤超低排放清洁燃烧具有重要科学意义和应用价值。

本研究通过开发不同种类的Fe基氧化物催化剂，利用自行搭建的催化剂脱硝脱汞活性测试实验系统，研究活性组分、载体种类、煅烧条件等催化剂制备工艺以及反应温度、烟气气氛等热力学/动力学反应参数对催化剂性能的影响规律。并且采用X射线衍射、扫描电镜、比表面积孔结构分析和电子能谱分析等表征手段对催化剂微观结构和理化性质进行分析测试，以深入探究影响催化剂催化活性的关键因素。实验结果表明：氧化铁质量分数为9%时催化剂的脱硝脱汞性能较高，Fe/Ti催化剂煅烧温度在500℃以下，煅烧时长在4h以内，催化剂脱硝脱汞效率较高。烟气中的水蒸气在催化剂表面会与反应气体发生竞争吸附，从而使得催化剂效率降低；二氧化硫不仅与反应气体竞争吸附，而且会消耗催化剂活性组分，从而严重抑制催化剂性能；氯化氢为反应提供活性氯原子，可以有效提高催化剂的脱汞效率。通过化学反应动力学分析，阐释明晰催化剂对氮氧化物与汞的脱除作用机理，进而为适宜燃煤电厂广泛应用的廉价高效脱硝脱汞催化剂的研制开发提供重要基础数据和有益技术指导。