前驱体对Ba/(Pt/γ-Al_2O_3)催化剂NO_x存储性能的影响

Influence of Ba Precursors on NO_x Storage Property of Ba/(Pt/γ-Al_2O_3) Catalysts

分别以Ba(NO3)2和Ba(CH3COO)2为Ba的前驱体,利用浸渍法制备了两个系列不同Ba含量的NOx存储还原催化剂Ba/(Pt/γ-Al2O3).采用X射线衍射、X射线光电子能谱、程序升温反应脱附和差热-热重等分析技术对样品进行了表征,并考察了催化剂的NOx存储性能.结果表明,不同前驱体在Pt/γ-Al2O3载体表面的分散能力不同.前驱体为Ba(NO3)2时,Ba的分散阈值为0.047 g/g(Ba/(Pt/γ-Al2O3)质量比),而前驱体为Ba(CH3COO)2时,Ba的分散阈值为0.149 g/g(Ba/(Pt/γ-Al2O3)质量比).经高温焙烧后,前驱体的分散容量决定催化剂中Ba物种的分散容量.在NOx存储性能评价实验中,以Ba(CH3COO)2为前驱体时,催化剂的NOx等温吸附穿透时间最长为23 min,而以Ba(NO3)2为前驱体时,具有相同Ba含量的催化剂的穿透时间为13 min.因此,在制备NOx存储还原催化剂时,选择易分散的前驱体Ba(CH3COO)2可以获得较高的NOx存储活性的催化剂.

NOx storage-reduction catalysts, Ba/（Pt/γ-Al2O3）, were prepared by the impregnation method using Ba （NO3）2 and Ba（CH3COO）2 as the barium precursors. Characterization studies of the catalysts were performed by means of X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reaction desorption, and differential thermal analysis-thermogravimetry. The results indicate that the dispersion threshold of Ba （NO3）2 is 0.047 g/g （Ba/（Pt/γ-Al2O3） mass ratio）, which is only about 1/3 of that of Ba（CH3COO）2. After the calcination treatment, the threshold of barium for the catalyst using Ba（CH3COO）2 as the precursor is larger than that using Ba （NO3）2 as the precursor. As a result, the Ba/（Pt/γ-Al2O3） catalyst prepared from Ba （CH3COO）2 has a higher NOx storage capacity than the catalyst prepared from Ba（NO3）2.