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摘要
In this study, Pt-K/TiO2 LNT catalysts having different K loadings (2, 5, 10, 15, 20 wt%) have been synthesized, characterized and tested, along with a Pt/K2Ti6O13 reference material. The effects of K loading and thermal aging on NOx storage performance have been addressed, and the formation/decomposition of stored NOx species over Pt-free samples has been investigated by FT-IR, TPD and XRD techniques. NOx storage-reduction tests of Pt-K/TiO2 catalysts indicate that 10 wt% K-loaded samples show the highest NOx storage capacity, registered at 300 degrees C. Both the temperature at which the maximum NOx storage capacity is attained and the NOx uptake yields are a function of the K-loading. A low K utilization in the NOx storage has been observed. Especially at high K contents (K= 20 wt%) this result can be attributed, in part, to the low surface area of the support material, and to the depletion of the K storage phase via reaction between K and TiO2. In fact XRD analyses demonstrate that K and TiO2 react already during the catalyst synthesis calcination process by forming a "K2Ti6O13-like" potassium titanate at temperatures as low as 550 degrees C. This reaction is promoted by increasing the K content and calcination temperatures. Activity, XRD and FT-IR measurements have demonstrated that poorly crystalline potassium titanates have appreciable storage properties. Upon aging treatments, K incorporates into the TiO2 structure, leading to the formation of potassium titanates: this increase in the stability of K, on the other hand decreases the NOx storage capacity. This raises questions concerning the capability of such systems to meet the durability requirements for vehicle emission control applications.
- 出版日期2016-2
