担载型Co/ZSM-5催化剂表面Co组分结构与柴油车NO_x净化性能  

Effect of Dispersion Structure of Co Constituents on the Activity of the Supported Co/ZSM-5 Catalysts for the De-NO_x of Diesel Vehicles

作　　者：唐富顺[1] 赵辉[1] 刘津[1] 陈梦寅 阮乐[1] 

机构地区：[1]桂林理工大学化学与生物工程学院广西电磁化学功能物质重点实验室,广西桂林541004

出　　处：《分子催化》2015年第3期256-265,共10页Journal of Molecular Catalysis(China)

基　　金：广西科学研究与技术开发计划项目(No.12118022-6);桂林理工大学博士基金(No.002401003321)

摘　　要：在摸拟轻型柴油车尾气的反应装置上,结合多种物理化学手段研究了富氧条件下Co/ZSM-5催化剂上Co组分分散状态及其C3H8选择性催化还原NOx性能.结果表明,浸渍法制备的Co/ZSM-5催化剂,ZSM-5表面Co的分散容量约为4.5%,当Co担载量高于4.5%时,Co物种开始在分子筛表面聚集形成Co3O4晶体,发生在Co3O4晶体上强的NOx吸附脱附,对富氧条件下C3H8选择性催化还原NOx是不利的.催化剂上孔内的钴物种主要以Co2+离子形式存在,而孔外表面既存在Co3+物种,也存在Co2+物种,Co3+的相对量随Co担载量的增加而增大.在催化剂孔外表面形成的以Co3+和Co2+结合的含有Co-Co键的低聚态Co Ox物种具有较合适的NOx吸附脱附性能和较强的氧化还原性,是富氧条件下C3H8选择性催化还原NOx反应的主要活性中心,反应需要在相邻的两个Co2+和Co3+活性位上完成.Under the simulated conditions of light-duty diesel vehicles exhaust,the effect of the dispersion structure of Co constituents on the selective catalytic reduction of NOxby C3H8(C3H8-SCR) over the supported Co / ZSM-5catalysts prepared by impregnation was studied by various experimental techniques. Results showed that the dispersion capacity of Co on the surface of Co / ZSM-5 catalysts prepared by impregnation was about 4. 5% measured by XRD,the Co3O4 crystallites were formed above the dispersion capacity,and the strong NOxadsorption occurring on the Co3O4 crystallites was disadvantageous to the selective catalytic reduction of NOxby C3H8. The Co species of Co / ZSM-5 catalysts were located the internal channel surfaces mainly in the form of Co2 +ions while both of Co3 +and Co2 +species were distributed at the external surfaces,the relative amount ratio of Co3 +ions increase with the increase of Co loadings. The oligomeric Co Oxspecies containing Co—Co bond were on the combination of Co3 +and Co2 +on the external surfaces of Co / ZSM-5 catalysts. The oligomeric state of Co Oxspecies with a better suitable NOx adsorption-desorption performance and strong Redox properties,was the chief active center of the selective catalytic reduction of NOxby C3H8 under oxygen-enrich condition. The SCR reaction needed to be completed in two adjacent Co2 +and Co3 +active sites by supposition. The C3H8-SCR activity of Co / ZSM-5 catalyst prepared by impregnation was closely related to the dispersion state,Redox properties and NOxadsorption-desorption performance of Co Ox species under the oxygen-enrich condition.

关 键 词：柴油车尾气 Co/ZSM-5催化剂 分散结构 CoOx物种 NOx净化 活性中心 

分 类 号：O643.36[理学—物理化学] X734.2[理学—化学]