【作者】 王海强；

【导师】 吴忠标；

【作者基本信息】 浙江大学 ， 环境工程， 2007， 博士

【摘要】 本文围绕着烟气氮氧化物氧化这一湿法脱硝的关键技术问题，重点研究了NO的光催化氧化技术。系统研究了TiO₂光催化剂制备工艺（溶胶-凝胶法，水热法），考察了过渡金属离子、贵金属离子掺杂对TiO₂光催化氧化NO活性的影响。最后，提出了一种光催化氧化结合液相吸收的湿法脱硝新工艺。首先，采用模拟烟气，考察了氮氧化物在光催化氧化体系中的反应特性，讨论了水蒸气含量、氧气含量等主要因素的影响。研究结果表明，NO的光催化氧化符合Langmuir-Hinshelwood动力学模型。傅立叶红外光谱的分析结果表明，催化剂表面的硝酸、亚硝酸沉积是造成催化剂失效的主要原因，500℃下30 min的灼烧是一种比较简便、有效的催化剂再生方式。其次，以氮氧化物的光催化氧化活性为考察指标，结合XRD、TEM、TG-DSC、SEM、UV-Vis等表征手段，系统研究了纳米TiO₂的溶胶-凝胶法制备工艺，主要研究对象包括钛水比、钛醇比、钛酸比以及灼烧温度等。研究发现，溶胶制备的工艺条件对TiO₂催化剂的结构和催化活性存在较大的影响。同时本文提出了一种在溶胶中加入空间填充物（纳米TiO₂）的复合TiO₂膜制备工艺。同时，结合XRD、TEM、TG-DSC、SEM、UV-Vis等表征手段，本文也平行研究了纳米TiO₂的水热法制备工艺对光催化氧化NO活性的影响。研究结果表明，存在较佳的水热温度、水热时间以及灼烧温度。基于以上研究基础，制备了不同过渡金属离子Zn²⁺、Fe³⁺、Cr³⁺、Mn²⁺和Mo⁶⁺掺杂的TiO₂光催化剂，考察了制备方法、不同金属离子以及掺杂浓度对改性TiO₂光催化氧化NOx的性能影响。研究发现，溶胶-凝胶法以及浸渍沉淀法制各的Zn离子掺杂TiO₂，其NO的氧化性能得到了较大提高。同时还制备了不同贵金属离子Ag⁺、Au³⁺和Pt⁴⁺表面沉积的TiO₂光催化剂，分别考察了不同贵金属离子以及不同贵金属离子沉积浓度对改性TiO₂光催化氧化NOx的性能影响。研究表明，Pt的表面沉积对TiO₂光催化氧化NO具有良好的促进作用。最后，本文提出了一种光催化氧化结合液相Na₂SO₃吸收的湿法脱硝工艺，对接近实际烟气中NOx浓度的模拟烟气进行处理，考察了光催化氧化以及液相吸收的关键影响因素对该脱硝工艺的脱硝效率的影响。研究表明，相对湿度、氧含量对整体的脱硝效率有较大的影响；Na₂S₂O₃的加入对Na₂SO₃的过度氧化具有良好的抑制效果。同时根据上述研究结果，探讨了该湿法脱硝工艺的反应机理。更多还原

【Abstract】 For the wet absorption of nitrogen oxides （NOx） from flue gases, the main obstacle is its rather low efficiency, since the solubility of NO is quite low. Thus, the oxidation of NO to increase the solubility of NOx is the key technology in this process. This dissertation presented the theoretic and experimental study on the photocatalytic oxidation （PCO） of NO on TiO₂-based photocatalyst, which was prepared by different methods including sol-gel method and hydrothermal method. The effects of transition metal ion doping and noble metal ion doping on the photocatalytic activity were also investigated in this dissertation. Furthermore, a novel combined process combining the photocatalytic oxidation with the aqueous absorption was developed and experimentally studied.Firstly, the PCO behavior of NO at high concentrations was discussed. And the relationship between the reaction rate and several key factors （relative humidity, space time, inlet concentration, oxygen percentage） was also investigated. The experimental results illustrated that the reaction kinetic of NO photocatalytic oxidation fitted well with the Langmuir-Hinshelhood model. The results from Fourier transform infrared spectrometry （FT-IR） showed that the possible explanation for the catalyst deactivation was the deposition of nitric acid and nitrous acid on the TiO₂ surface. Fortunately, the activity of the photocatalyst could be regenerated with a simple efficient heat treatment （500℃, 30 min）.Secondly, with the attention to photoactivity for NO oxidation, the optimization of the preparation conditions by sol-gel method and hydrothermal method was carried out in the dissertation. The characterizations for the physicochemical properties of the catalysts prepared under different conditions were investigated by XRD, TEM, TG-DSC, SEM and UV-Vis methods. It was found that the preparing conditions have great effects on the PCO activities of the catalysts. And the optimal values of the two preparing methods were discussed, respectively. Furthermore, the composite TiO₂ films （using Degussa P25 as filler） coating on the woven glass fabric were prepared by a modified sol-gel process, and the experimental results show that the photoactivity of composite TiO₂ film could have an obvious improvement compared to the single films.Thirdly, a series of transition metal ion-doped (such as Zn²⁺、Fe³⁺、Cr³⁺、Mn²⁺ and Mo⁶⁺) TiO₂ catalysts with different ion content had been prepared by sol-gel method or wet impregnation method. These catalysts were examined with respect to their photocatalytic activity under different preparing methods, metal ion types and the doping contents. An enhancement of the photocatalytic activity was accomplished for the Zn²⁺ doped TiO₂ catalysts which synthesized by sol-gel method or wet impregnation method. Also, a series of nano-sized noble metal ion-doped (Ag⁺、Au³⁺ and Pt⁴⁺) TiO₂ catalysts with different ion contents was prepared by a wet impregnation method and examined with the respect to their behaviors for the photocatalytic oxidation of NO. It was found that the Pt⁴⁺ doped TiO₂ catalyst had the highest photoactivity for NO, which was attributed to the lengthened lifetime of electron-hole pairs.Finally, a novel process combining photocatalytic oxidation with aqueous absorption was developed in this study for the treatment of nitrogen oxides from the simulated flue gases. In this process, sodium sulfite （Na₂SO₃） was employed as the absorbent. The effects of the operation parameters of this combined process （relative humidity, space time, inlet concentration, and so on） were investigated and the reaction mechanism was proposed. The results indicated that the relative humidity and oxygen percentage were the key factors of the combined process. And Na₂S₂O₃ was an excellent oxidation inhibitor to prevent the excessive oxidation of sulfite.更多还原