氧化铈基脱硝催化剂的储/释氨特性及其机理研究

DeNOx has become the governance focus of fog and haze, because NOx is one of the main causes for the fog and haze. An initial domestic technology of environment-friendly and efficient Ceria-based (CeO2/TiO2) deNOx catalyst successfully breaks the foreign technology monopoly of the toxic deNOx catalyst system of V2O5/TiO2. In its industrial applications, it suddently exhibits the new excellent characteristics of ammonia storage and release, which were never seen before in the same SCR deNOx engineering using the Vanadia-based deNOx catalyst. Especially the ammonia storage-release characteristics have important contributions on mataining the stability of deNOx efficiency under condition of flue gas fluctuation, and on decreasing ammonia escape and so on. For the first time this project will deeply study this new discovery that the ammonia storage-release characteristics of the Ceria-based deNOx catalyst. In order to fully explore the ammonia storage-release behaviors, the ammonia storage-release capacities and their influncing factors, and also to focus on revealing the existing forms of the excess ammonia that were not involved in the SCR reaction and revealing their effective release ways, the diffusion, adsorption and activation theory and advanced materials characterization methods will be used through the research work, and the innovative design will focus on ammonia storage-release experimental scheme in constant temperature gas flow field. This will allow us to discover the cause of ammonia storage-release characteristicsthe and the mechanism, and consequently to provide a solid and innovative engineering theory that one can take it as a basis for establishing the optimum ammonia storage-release condition and mastering its adjustment measures, mataining stability of NH3-SCR deNOx efficiency, decreasing ammonia injection and escape, and decreasing the deNOx cost; and consequently to provide a theoretical basis and technical support for expanding the application of the ammonia storage-release characteristics of the Ceria-based catalyst in other ammonia industries.

脱硝是雾霾治理的重点，我国自主首创的环境友好高效氧化铈基（CeO2/TiO2）脱硝催化剂技术，打破了国外有毒钒钛体系（V2O5/TiO2）脱硝催化剂技术的垄断；在产业化应用中突显出钒钛体系催化剂所不具备的储/释氨优异特性，对稳定烟气波动工况下的脱硝效果、减少氨逃逸等有重要贡献。本课题对氧化铈基脱硝催化剂的储/释氨特性这一全新发现进行深入研究，运用扩散、吸附及活化理论和先进的材料表征手段，创新设计恒温气流场中催化剂储/释氨实验方案，全面探索储/释氨行为过程、储/释氨量及影响因素，着重揭示催化剂上尚未参与SCR脱硝反应的多余氨的存在形态及有效释放方式，解明储/释氨特性的成因与机理。为确立最佳储/释氨条件及调控措施，稳定NH3-SCR脱硝效果，削减氨逃逸，减少喷氨量，降低脱硝运行成本，提供坚实而富有新意的工程理论基础；为拓展氧化铈基催化剂的储/释氨特性在其他氨工业中应用，提供理论依据和技术支撑。

脱硝是大气污染治理的重点，我国自主首创的环境友好高效氧化铈基脱硝催化剂技术打破了国外有毒钒钛体系脱硝催化剂技术的垄断；在工程应用中突显出钒钛体系催化剂所不具备的储/释氨优异特性，对稳定烟气波动工况下的脱硝效果、减少氨逃逸等有重要贡献。本项目针对氧化铈基脱硝催化剂的储/释氨行为、机理及其影响因素等进行了深入研究，优选CeSnWBaOx/TiO2和CeSnMoOx/TiO2两种代表性氧化铈基脱硝催化剂为研究对象，创新设计了恒温气流场实验，结合in situ DRIFTS、NH3-TPD、N2吸附/脱附、SEM等表征手段，取得如下创新结果：氧化铈基脱硝催化剂的有效储氨是稳定其波动工况脱硝效率的前提，其主要以物理和化学两种方式储存：氨气分子扩散到催化剂内外表面和孔道，通过物理吸附和“口袋”封存于催化剂中；催化剂与氨之间通过酸碱吸附与活化，形成新的化学吸附态氨物种NH4+*、-NH和配位态NH3等。低温储氨量大，但速率较低；高温储氨速率较快，但储氨量小；由于活性位活化，从250℃开始化学吸附氨增加。单位比表面积催化剂50℃的稳定储氨量达22.97μmol•m-2，随温度上升，部分NH4+*和-NH物种减少，而配位态NH3增加。储氨的有效释放是关键，主要以化学吸附氨物种参与SCR反应和少量氨分子热运动逃逸两种方式释放。化学吸附氨物种会在NO的诱导下参与SCR反应，NO浓度越高，越有利于诱导催化剂的有效释氨，在闭氨阶段能够维持脱硝效率不低于行业NOx排放限值100mg•Nm-3的有效释氨量为0.392μmol•m-2。储氨有强有弱，受温度、空速及NO诱导影响大。250-300℃低温段释氨量多，维持工况高活性时间长；350℃以上高温释氨快。低空速有利于有效释氨并充分参与SCR脱硝反应，在NO诱导下，释氨较储氨过程快。催化剂饱和储氨下的有效利用量随着温度升高而降低，但相对稳定储氨量的有效利用率呈先升高后下降趋势，300℃以上仍有＞50%的利用率。氧化铈基脱硝催化剂具有比钒基催化剂更低的反应活化能，能使其在较低的温度下进行大量的有效释氨并参与SCR反应。以上成果为确立氧化铈基脱硝催化剂在工程应用中的最佳储/释氨条件及调控措施，减少喷氨量及降低脱硝运行成本提供了坚实而富有新意的工程理论基础。