论文部分内容阅读
采用分步浸渍法制备不同CeO_2含量改性SiO_2-Al_2O_3载体的Pt/SiO_2-Al_2O_3柴油车氧化催化剂Pt/SiO_2-Al_2O_3-wCeO_2(质量分数w为0%,5%,10%,15%,30%)。利用固定床反应器,在模拟柴油车行驶条件下测定催化反应活性。活性结果表明,无论CO和C3H6存在与否,适量CeO_2的添加均明显提高了Pt/SiO_2-Al_2O_3柴油车氧化催化剂的NO氧化性能。其中,Pt/SiO_2-Al_2O_3-15%CeO_2表现出了最优氧化性能,其能在较宽温度范围内维持61%的NO_2产率。CO-化学吸附结果表明,适量CeO_2的添加有利于提高Pt的分散度,即提高催化剂表面可利用Pt原子比例。透射电镜(TEM)结果证实了CeO_2改性后高分散的Pt颗粒的存在,X射线衍射(XRD)结果也说明CeO_2改性后的载体更利于抑制Pt晶粒的增长。氢气程序升温还原(H2-TPR)和TEM结果均说明CeO_2的添加增强了贵金属-载体间的相互作用,从而更利于PtO_x与CeO_2还原。总之,本文表明CeO_2改性柴油车催化剂(DOC)可以提高催化剂的分散性和还原性,从而提高NO催化氧化性能,其对工业应用中柴油车尾气净化后处理复合系统(DOC+DPF+SCR)的净化效率的提高有重要意义。
The Pt / SiO_2-Al_2O_3-wCeO_2 catalyst for Pt / SiO_2-Al_2O_3 diesel oxidation with different CeO_2 modified SiO_2-Al_2O_3 supports was prepared by a stepwise impregnation method. The mass fraction w was 0%, 5%, 10%, 15%, 30 %). Catalytic activity was measured using a fixed bed reactor under simulated diesel vehicle conditions. The results of the activity show that the NO oxidation performance of the Pt / SiO_2-Al_2O_3 diesel oxidation catalyst is obviously increased with the addition of the proper amount of CeO_2, regardless of the existence of CO and C3H6. Among them, Pt / SiO 2 -Al 2 O 3-15% CeO 2 showed the best oxidation performance, which can maintain 61% NO 2 yield over a wide temperature range. CO-chemisorption results show that the appropriate amount of CeO 2 is conducive to increasing the dispersion of Pt, that is, increasing the proportion of Pt atoms available on the surface of the catalyst. Transmission electron microscopy (TEM) results confirmed the presence of highly dispersed Pt particles modified by CeO 2. The results of X-ray diffraction (XRD) also showed that the CeO 2 modified carrier was more effective in inhibiting the growth of Pt grains. Hydrogen temperature-programmed reduction (H2-TPR) and TEM results indicate that the addition of CeO 2 enhances the interaction between noble metal and support, which is more conducive to the reduction of PtO_x and CeO_2. In summary, this paper shows that CeO 2 modified diesel catalyst (DOC) can improve the dispersibility and reducibility of the catalyst and thus improve the catalytic activity of NO oxidation. The catalytic oxidation of DOC (DPO + SCR) Purification efficiency is of great significance.