新型改性氧化铈催化剂低温脱硝协同脱汞机理研究

Coal-fired industrial boiler is one of the main NOx emission sources in China, it is necessary to control the NOx emission from them. At present, NH3-SCR is the most widely used technology for NOx elimination. V2O5-WO3/TiO2, the traditional SCR catalyst, which has an operation window higher than 300 C, is not applicable for industrial boilers since most of the temperature of flue gases is lower than 250 C. To control the NOx emission from domestic industrial boilers, it is urgent to develop low-temperature DeNOx catalyst which could be applied under practical conditions in flue gas. The biggest obstacle for low-temperature DeNOx catalyst is its resistance to SO2 and H2O. Up to now, there is no efficient way to solve this problem. In this project, a novel way of combining low-temperature DeNOx with synergistic mercury removal via regeneration was proposed. Firstly, the low-temperature SCR performance of Ce-based catalyst is going to be improved by modification with assistants. Secondly, the stability of surface sulfates, which form after SO2 poisoning, will be weakened by addition of Ge. Thus, the temperature of regeneration is decreased. Finally, mercury removal activity will be enhanced by regulation of surface oxidation sites. Based on the previous work of the applicants, composite modification of Ce-based catalyst will be applied by doping with Mo and W. The catalyst formula will be optimized by preparation technology to improve its low-temperature DeNOx performance. A coupling model will be established between the stability of surface sulfate and NOx conversion. In order to reduce the regeneration temperature of deactivated catalyst, Ge will be doped to the catalyst. The mechanism of DeNOx and synergistic mercury removal at low temperatures will be discussed based on characterizations. This research will provide not only the experimental and mechanism study of DeNOx and synergistic mercury removal at low temperatures, but also a significant contribution to the comprehensive utilization of the rich rare earth metals resources in China.

燃煤工业锅炉是我国主要的NOx排放源之一，急需对其进行NOx排放控制。目前，应用最广泛的NOx控制技术是NH3-SCR技术。然而，传统的SCR催化剂操作温度在300℃以上，对工业锅炉烟气（一般温度低于250℃）难以适用。开发适合我国工业锅炉烟气排放特征的低温脱硝催化剂成为亟待解决的问题。SO2和水蒸汽中毒是低温脱硝面临的最大障碍，至今难以有效解决。本项目提出通过循环再生实现低温脱硝协同脱汞的思路，开发新型改性氧化铈催化剂实现高效低温脱硝，添加锗等助剂降低其再生温度，通过调控催化氧化位分布实现协同脱汞。 本研究拟在已有工作基础上，掺杂钼钨等助剂对氧化铈进行复合改性，优化制备工艺以获得低温活性好的催化剂。在硫酸盐稳定性和脱硝效率耦合模型建立的基础上，添加锗等降低催化剂再生温度，探索低温脱硝协同脱汞反应机理。本研究不仅为低温脱硝协同脱汞提供理论基础，而且对于我国丰富的稀土金属资源综合利用具有重要意义。

氮氧化物（NOx）控制和汞净化是燃煤工业锅炉面临的重要课题。近年来，宽温度窗口下高效脱硝协同脱汞引起了研究者的广泛关注。本课题针对燃煤工业锅炉烟气中的NOx和汞排放问题，以新型铈基催化剂为基础，开展新型改性氧化铈催化剂低温脱硝协同脱汞机理研究，完成的研究工作主要分为四个方面：1）新型氧化铈催化剂设计与制备；2）铈基催化剂磷中毒机制与抗中毒性能改进；3）催化剂HCl和SO2中毒及酸性气体中毒机制探讨；4）酸、碱位上协同脱硝脱汞反应机理研究。.首先，以硫酸铈为前驱体通过水热法制备的CeO2-SH催化剂在230-450℃表现出优异的SCR活性和很高的氮气选择性。此外，该催化剂的抗碱金属（比如钠、钾等）中毒性能也有所提高。进一步开发的铈钼复合氧化物催化剂比VMo/Ti催化剂在氮气选择性和磷耐受性方面表现出更好的效果。同时，铈钼催化剂表现出了对H2O和SO2良好的耐受性，表明铈钼复合氧化物催化剂是一种工业烟气脱硝所使用的钒基催化剂的理想替代物，尤其是对磷含量高的烟气。.在深入研究HCl和SO2中毒基础上，我们提出了酸/碱耦合与氧化还原性能关联的酸中毒机制。根据该机制，催化剂有两个重要的相关连的性能—酸-碱性和氧化还原性。酸性有利于NH3在SCR反应中的吸附。催化剂的M-O 或 M-OH活性位的酸-碱性质和氧化还原性能是相互关联的。碱性位的分布和强度是影响中低温HCl和 SO2中毒的关键因素。HCl等易和强碱性O2-离子相互作用，导致催化剂氧化还原循环的破坏和酸碱中心-OH基团的生成。前者导致了低温SCR活性的降低。同时，在中毒后NH3的过氧化和N2O的生成被抑制。该创新性机理的提出有助于对SCR催化剂中毒机制的理解。.最后，通过研究催化剂同时去除NOx和Hg0的性能，揭示了SCR催化剂表面酸碱性与协同脱除NOx和Hg0催化剂的活性和稳定性的内在联系。另一方面，通过研究NH3对Hg0氧化的抑制作用发现Hg0和NH3在表面酸性位存在竞争吸附关系。研究结果指出，利用SCR催化剂协同Hg0氧化过程中，表面的酸性位和碱性位调控是防止催化剂酸性气体中毒和高效协同除Hg0的关键。