基于相反脱汞特性对比的单质汞催化剂二氧化硫中毒机理及其改性研究

The harm to the environment caused by mercury from coal-fired flue gas is becoming more serious. Thus, the emission of mercury must be effectively controled. The technology for elemental mercury catalytic oxidation by using the catalyst and O2 to oxidized mercury which can be desorbed with pyrolysis and collected for reutilization has broad application prospects. However, the SO2 poisoning of the catalyst should be overcome. While at present, the mechanism of the catalyst deactivation caused by SO2 is not clear. In this project, focusing on the opposite Hg removal performance of how can SO2 promote the catalytic oxidation of Hg0 over Ce/TiO2 and inhibit over Mn/TiO2 catalyst, the SO2 poisoning mechanism analysis are carried out. The physicochemical properties of the catalysts are characterized by in situ DRIFTS, XAFS, XPS and other necessary characterization techniques. The reaction path of SO2 over the two catalysts are studied. The various influence factors and inherent correlation of promotion and inhibition caused by SO2 are also explored. Furthermore, to prove the mechanism of promotion and inhibition over the two catalysts in the process of Hg0 capture, the composition of sediment on the catalyst surface, the evolution and coordination environment of the main elements are investigated. Moreover, to impove the distribution of surface groups and activity center and obtain higher sulfur poisoning resistance, the modified catalysts are prepared by doping transition metal or rare earth elements. Through the above research, the important theoretical and scientific basis for in-depth understanding the mechanism of SO2 poisoning and the mercury capture catalyst design with higher sulfur poisoning resistance can be provided.

燃煤烟气中汞对环境的危害日趋严重，必须得到有效控制。利用催化剂和O2将单质Hg转化为氧化态Hg后热解、收集、资源化的技术具有广泛的应用前景，但催化剂需克服SO2的毒化。目前，催化剂SO2中毒的机理尚不明确。本项目拟采用Ce/TiO2和Mn/TiO2两种典型单质汞催化剂，围绕SO2促进Ce/TiO2对单质Hg的氧化而抑制Mn/TiO2对单质Hg的氧化这一相反脱汞特性开展催化剂SO2中毒机理研究。通过DRIFTS、XAFS和XPS等必要手段研究SO2在催化剂表面的反应历程；探寻SO2对两种催化剂促进/抑制作用的各种影响因素和内在关联；明确催化剂表面沉积物的具体成分、主要元素的迁徙规律和配位环境；探明SO2在反应中的促进/抑制机理。通过过渡金属或稀土元素掺杂改性催化剂，改善表面基团和活性中心分布以提高其抗硫能力，为深层次阐明催化剂SO2中毒机制和设计抗硫催化剂提供重要理论基础和科学依据。

环境问题已成为制约我国经济和社会健康发展的重要因素之一。燃煤烟气的汞污染是全球性问题，必须得到有效控制。利用催化剂和O2将Hg0转化为氧化态Hg后热解、收集、资源化的技术具有广泛的应用前景，但催化剂/吸附剂需克服SO2的毒化。目前脱汞催化剂的研究仍处于探索阶段，导致催化剂SO2中毒的机理尚不明确。基于此，本项目研究了煅烧温度对锰基（MnOx-TiO2和MnOx-CoOy/TiO2）催化剂的脱汞性能及物化结构的影响；研究了制备方法对MnOx-TiO2催化剂脱汞活性及抗硫性的影响；研究了Ru、Cr改性MnOx-TiO2催化剂的脱汞活性及抗硫能力，明确了催化剂表面沉积物的具体成分及Ru、Cr、Mn、Hg和S的赋存形态；研究了SO2参与铈基（CeO2-TiO2）材料的脱汞活性及抗硫中毒机理，揭示了SO2促进CeO2-TiO2催化剂脱汞的机制。主要结论如下：（1）催化剂的脱汞活性与煅烧温度和制备方法密切相关。沉积-沉积法和溶胶-凝胶法制备的催化剂会引起MnOx还原性和分散度的增强，会使活性成分由本体到表面的迁移，促进其高效脱汞；（2）RuOx添加不仅可以大幅提高MnOx-TiO2催化剂的脱汞活性，亦可以大幅增强其抗硫能力。Ru、Mn和氧之间形成的无定形结构及其之间的协同作用在促进Hg0的高效脱除和高抗硫方面起关键作用。SO2会优先与催化剂中的RuOx反应，有效保护催化剂的活性成分MnOx；（3）MnOx-TiO2吸附剂中添加CrOx可以提高其脱汞活性和增强其抗硫性；尽管CrOx-MnOx-TiO2具备较强的脱汞和抗硫能力，但CrOx的硫酸化仍会发生，SO2中毒后CrOx-MnOx-TiO2中铬价态由Cr6+变至Cr3+；（4）随着CeO2-TiO2（CeTi）硫酸化时间的延长，由于大量硫酸铈盐的存在，SO2对Hg0的脱除效率逐渐降低。硫化后CeTi的还原性会降低，硫酸化会引起催化剂表面Ce3+含量的增加。SO2参与的CeO2-TiO2脱汞过程中，CeO2(Ce4+)与Ce2O3(Ce3+)之间的氧化还原反应对其高效脱汞发挥重要作用。Ru、Cr改性的MnOx-TiO2材料和Ru改性的CeO2-TiO2材料具有优异的脱汞性能和抗硫能力，它们具有广阔的商业应用前景，研究成果为燃煤烟气脱汞技术的完善提供了重要的理论与科学基础。