Evaluation of H2 Influence on the Evolution Mechanism of NOx Storage and Reduction over Pt-Ba-Ce/γ-Al2O3 Catalysts

摘要

In this investigation,Pt-Ba-Ce/γ-Al2O3 catalysts were prepared by incipient wetness impregnation and experiments were performed to evaluate the influence of H2 on the evolution mechanism of nitrogen oxides (NOx) storage and reduction (NSR).The physical and chemical properties of the Pt-Ba-Ce/γ-Al2O3 catalysts were studied using a combination of characterization techniques,which showed that PtOx,CeO2,and BaCO3,whose peaks were observed in X-ray diffraction (XRD) spectra,dispersed well on the γ-Al2O3,as shown by transmission electron microscope (TEM),and that the difference between Ce3+ and Ce4+,as detected by X-ray photoelectron spectroscopy (XPS),facilitated the migration of active oxygen over the catalyst.In the process of a complete NSR experiment,the NOx storage capability was greatly enhanced in the temperature range of 250-350℃,and reached a maximum value of 315.3 μmol·gcat-1 at 350 ℃,which was ascribed to the increase in NO2 yield.In a lean and rich cycling experiment,the results showed that NOx storage efficiency and conversion were increased when the time of H2 exposure (i.e.,30,45,and 60 s) was extended.The maximum NOx conversion of the catalyst reached 83.5％ when the duration of the lean and rich phases was 240 and 60 s,respectively.The results revealed that increasing the content of H2 by an appropriate amount was favorable to the NSR mechanism due to increased decomposition of nitrate or nitrite,and the refreshing of trapping sites for the next cycle of NSR.