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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.
In the reaction device simulating the exhaust of light diesel vehicle, the Co component dispersion state on Co / ZSM-5 catalyst under oxygen enrichment conditions and the selective catalytic reduction of NOx by C3H8 were studied by means of various physicochemical methods.The results showed that impregnation The Co / ZSM-5 catalyst prepared by the method has a Co content of about 4.5% on the surface of ZSM-5. When the Co loading is higher than 4.5%, the Co species begin to aggregate on the surface of the molecular sieve to form Co3O4 crystal, which occurs on the Co3O4 crystal The strong NOx adsorption and desorption is disadvantageous for the selective catalytic reduction of NOx by C3H8 in oxygen-rich conditions.The cobalt species in the pores of the catalyst mainly exists as Co2 + ions, while the outer surface of the pores has both Co3 + species and Co2 + species, The relative amount of Co3 + increases with the increase of the Co loading.The Co-Co bond-containing oligomeric Co Ox species formed on the outer surface of the catalyst pores with Co3 + and Co2 + have the more suitable NOx adsorption and desorption properties and The strong redox activity is the main active site for the selective catalytic reduction of NOx with C3H8 under oxygen-rich conditions, and the reaction needs to be completed at two adjacent Co2 + and Co3 + active sites.