关键词: 氮氧化物储存还原, 氧化锆, 二氧化钛, 载体, 碳酸钾, 铂, 焙烧温度, 结构表征

Abstract: The effects of support calcination temperature on the NOx storage capacity of the K/Pt/TiO2-ZrO2 catalyst were studied byX-raydiffraction (XRD), NH3 temperature-programmed desorption (TPD), N2 adsorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). The XRD results indicate that the catalyst is amorphous with support calcined at 500 ℃. With the elevation of calcination temperature to 650 ℃, ZrTiO4 crystals are formed, whose crystallization becomes more and more complete at higher temperature up to1000℃. The results of NH3-TPD reveal that the support calcined at 500 ℃ possesses the biggest amount of acidic sites; however, it decreases remarkably as the calcination temperature increases. After calcination at1000℃, the support nearly loses all the acidity. The NOx storage capacity of the samples is not proportional to the BET surface area of the supports. The sample with the support calcined at 500 ℃ shows the lowest NOx storage capacity, whereas the sample with the support calcined at 800 ℃ exhibits the highest NOx storage capacity. The results of DRIFT show that NOx is stored as NO-3 and bidentate/monodentate nitrate species in the sample with the support calcined at 500 ℃, whereas only NO-3 species is detected in other samples with the support calcined at higher temperatures. As a result, the calcination temperature influences not only the structure and acidity of the support but also the interaction between the support and the supported components. The formation of the-OKgroup arising from the interaction between the surface hydroxyl groups of support and the K-containing phases is not favorable to NOx storage, while the highly dispersed K2CO3 phase facilitates the NOx storage as nitrate.

Key words: NOx storage and reduction, zirconia, titania, potassium carbonate, platinum, calcination temperature, structural characterization