CeO_2的添加对柴油车氧化催化剂Pt/SiO_2-Al_2O_3的NO氧化性能提高的影响（英文）

Effects of CeO_2 Addition on Improved NO Oxidation Activities of Pt/SiO_2-Al_2O_3 Diesel Oxidation Catalysts

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 catalytic activities for NO oxidation achieved by different amounts of CeO2-modified Pt/SiO2-Al2O3 catalysts Pt/SiO2-Al2O3-wCeO2 （the mass fraction w being 0%, 5%, 10%, 15%, 30%）, prepared using step-wise impregnation, were investigated in the presence and absence of CO and C3H6. The results showed that the NO oxidation activity could be efficiently improved by modification of CeO2 wherein the 15%-CeO2-modified catalyst exhibited the maximum NO conversion of 61% even in the presence of CO and O3H6, which were proved to inhibit NO2 formation in this study. A series of characterization methods were performed over the as-prepared samples to correlate their surface and structural characteristics with their enhanced NO oxidation activities. CO-chemisorption illustrated that appropriate CeO2-loading was effective for enhancing Pt dispersion, thus enhancing Pt surface-to-volume ratio, confirmed by transmission electron microscope （TEM） images. X-Ray Diffraction （XRD） further suggested that ceria addition could suppress the growth of the Pt crystal, resulting in higher surface Pt atomic ratio. Further, H2 temperature-programmed reduction （H2-TPR）, together with TEM results, implied that the presence of ceria could enhance the interaction between metal and supports, thus facilitating reducibility of both active platinum and ceria. Hence, this study displays that ceria could act as a dispersion promoter and a reducibility booster, both of which are beneficial to NO oxidation activity. The improved NO oxidation activity is significant for the efficient purification of diesel integrated catalytic system.