Mn-Ce/AC催化剂烧结烟气脱硝中毒失活机理研究

Sintering flue gas De-NOx is one of the major tasks for atmospheric pollution control of iron and steel industry in China. Mn-Ce activated carbon (AC) catalyst has good low temperature De-NOx activity and the capability of resistance to sulfur and water. However, the sintering flue gas also contains a small amount of alkali metals, alkaline earth metals and heavy metals, which will cause the catalyst poisoned and the catalytic activity to drop rapidly. Determining the poisoning mechanism is very important for the industrial application of Mn-Ce/AC catalyst in De-NOx process of the sintering flue gas. This project firstly studies the characteristics of sintering flue gas of typical iron and steel enterprises in China, and determines the content and existing state of the catalyst toxic components, and also determines their molecular characteristics. Secondly, the effect of single toxic component species, content and existing state on the De-NOx activity of the catalyst is studied, and a single component poisoning dynamic model will be established by combining SCR reaction mechanism. In addition, the mutual influences of different toxic components, and various poisoning components on the catalyst active component, surface functional groups and the carrier will be studied, determining the poisoning mechanism of the multicomponent poisoning condition; Based on the above, combining with the characteristics of actual sintering flue gas, the catalyst anti-poisoning measures and the regeneration method of inactivated catalyst will be proposed, which will provide theoretical basis and technical support for the industrial application of Mn-Ce/AC catalyst in the sintering flue gas De-NOx process of China.

烧结烟气脱硝是钢铁行业大气污染治理的重要任务之一，Mn-Ce/活性炭（AC）催化剂具有良好的低温脱硝活性及抗硫抗水能力。然而，烧结烟气含有少量的碱金属、碱土金属和重金属等，会使催化剂活性快速下降。确定烧结烟气条件下Mn-Ce/AC催化剂的中毒机理对其工业应用至关重要。本项目首先对我国典型钢铁企业烧结烟气组分特征进行研究，确定易使催化剂中毒组分的含量、赋存形态和分子本征特性；其次，研究烧结烟气中单一中毒组分的种类、含量及赋存状态对催化剂脱硝活性的影响规律，结合SCR反应机制，构建单一组分中毒动力学模型；再次，研究不同中毒组分间的相互影响及各中毒组分与催化剂活性组分、表面官能团和载体的作用机制，确定多中毒组分共同作用条件下催化剂的中毒机理；基于以上，结合实际烧结烟气特点，提出催化剂抗中毒措施及失活催化剂再生手段，为Mn-Ce/AC催化剂在我国烧结烟气脱硝的工业应用提供理论依据和技术支撑。

Mn-Ce/AC低温脱硝催化剂是目前用于烧结烟气脱硝较好的低温催化剂之一，虽然该低温SCR脱硝装置布置于除尘和脱硫装置之后，可以避免大量的飞灰和SO2的毒害，但烟气中仍然残留少量的粉尘及亚微米级别的钾、砷、锌和铅等有害元素及少量SO2，钾、砷、锌和铅等对催化剂的危害极大，催化剂长时间暴露在烧结烟气中容易受到这些有害物质的影响。因此，项目研究了钾、砷、锌和铅等对Mn-Ce/AC脱硝催化剂的中毒机理，弄清了催化剂脱硝过程的失活路径，为抗钾、砷、锌和铅等中毒催化剂的研发提供参考依据。在此基础上，项目通过有益元素掺杂策略来提高催化剂的抗中毒能力。ZnCl2中毒后，Mn-Ce/AC催化剂的NO转化率下降到35%，当负载Nb2O5后NO转换率恢复到约100%。SO2中毒后Mn-Ce/AC催化剂的NO转化率下降到30%，当负载Nb2O5后，NO转化率恢复到约80%。PbCl2中毒后NO转化率下降到35%，Sm和Fe共掺杂的Mn-Ce/AC催化剂在SO2和PbCl2存在的情况下NO转化率仍能达到80%。最后，本项目提出了一种失活催化剂再生技术，其流程如下：催化剂吹扫→水洗→酸洗→活性组分补充。通过该技术，在反应温度为225℃时，再生的Mn-Ce/AC催化剂脱硝活性由63.4%恢复到约98.5%。催化剂是SCR脱硝技术的核心部分，决定了SCR系统的效率和脱硝经济性。通过研究烧结烟气中的有害组分对催化反应的影响机制，不仅对丰富和完善催化剂中毒机理具有重要的意义，而且为解决催化剂中毒失活问题提供实验依据和理论指导，这对认识催化剂失活规律、延长催化剂使用寿命、降低烧结烟气脱硝成本、促进烧结烟气脱硝技术的推广应用具有重要的现实意义。