Ag Cluster Catalyst-Research of Reaction Mechanism and Development of Diesel deNOx Catalyst

从环境的角度来看，减少柴油发动机汽车的氮氧化物是一个严重的问题。研究发现，纳米至亚纳米尺度的Ag除尘器对于过量氧条件下未燃烧碳氢化合物（RIC-SCR）选择性还原NOx非常有效。本项目旨在通过原位光谱和DET计算揭示HC-SCR在Ag粉尘上的动力学和反应机理，以指导实际催化剂的设计。在项目实施期间，取得了以下成果：Ag-氧化铝的反应活性及反应机理：ESR谱分析表明，氢对Ag-氧化铝进行轻微还原形成的Ag-氧化铝与气态氧接触，形成超氧化物。阐明了银除尘器对氧活化的重要作用。此外，还提出了氢在氧的活化和银团簇形成中的作用。用DFP计算评价反应机理：用DFP计算评价氢对银粉尘的形成及其表面氧的活化作用。Ag 4元团簇（Ag_4^<2+>）在沸石笼中最稳定，这与EKAFS实验结果一致。氢化银粉（H-H-Ag_4^<2+>）与氧接触生成过氧化氢。由于过氧化氢对烃类ns氧化为含氧物质和NO氧化为NO23都具有活性，因此该模型可以对实验结果进行合理化。银粉剂在氢存在下的耐SOx性：通过优化还原剂种类、温度和共加氢，实现了银粉剂的高SOx耐受性。高的SIX容差是由于SOx从Ag表面迁移到气相或氧化铝载体造成的。

Reduction of NOx from diesel engine cars is serious problem from environmental points of view. We have found that Ag duster having the Size of nano to sub-nano scale is very effective for the selective reduction of NOx by unburned hydrocarbons RIC-SCR) in the excess of oxygen. The aim of this project is to reveal the dynamics and the reaction mechanism of HC-SCR over Ag duster by using in-situ spectroscopy and DET calculations in order to guide the design of practical catalysts. The following results have been obtained in the term of the project.1.Reactivity and reaction mechanism of Ag duster : It was hind by ESR spectrometer that the contact of gaseous oxygen and Ag duster formed by a slight reduction of Ag-alumina by hydrogen results in the formation of super-oxide species. The important role of Ag duster on the activation of oxygen was clarified. Furthermore, the role of hydrogen on the activation of oxygen and the formation of Ag cluster was suggested.2. Evaluation of reaction mechanism by DFP calculation: Formation of Ag duster by hydrogen and activation of oxygen on its surface was evaluated by DFP calculation. Ag 4-membered cluster (Ag_4^<2+>) is the most stable in zeolite cage, which is in harmony with the experimental results by EKAFS. The contact of hydrogenated Ag duster (H-H-Ag_4^<2+>) with oxygen results in the formation of hydrogen peroxide. The experimental results can be rationalized by this model, because the hydrogen peroxide is active for both oxidation of hydrocarbons ns to oxygenated species and NO to NO23. SOx tolerance of Ag duster in the presence of hydrogen: High SOx tolerance of Ag duster was achieved through optimization of the kind of reductants, temperature, and co-feeding of hydrogen. The high SIX tolerance is caused by migration of SOx from Ag surface to gas phase or alumina support.