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物理化学学报  2017, Vol. 33 Issue (6): 1242-1252    DOI: 10.3866/PKU.WHXB201703292
论文     
CeO2的添加对柴油车氧化催化剂Pt/SiO2-Al2O3的NO氧化性能提高的影响
黄于芬1,张海龙2,杨铮铮3,赵明1,黄木兰1,梁艳丽1,王健礼1,*(),陈耀强1,*()
1 四川大学化学学院,绿色化学与技术教育部重点实验室,成都610064
2 四川大学化学工程学院,成都610064
3 西华师范大学环境科学与工程学院,四川南充637009
Effects of CeO2 Addition on Improved NO Oxidation Activities of Pt/SiO2-Al2O3 Diesel Oxidation Catalysts
1 Key Laboratory of Green Chemistry & Technology of the Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, P. R. China
2 College of Chemical Engineering, Sichuan University, Chengdu 610064, P. R. China
3 College of Environmental Science and Engineering, China West Normal University, Nanchong 637009, Sichuan Province, P. R. China
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摘要:

采用分步浸渍法制备不同CeO2含量改性SiO2-Al2O3载体的Pt/SiO2-Al2O3柴油车氧化催化剂Pt/SiO2-Al2O3-wCeO2(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CeO2的添加均明显提高了Pt/SiO2-Al2O3柴油车氧化催化剂的NO氧化性能。其中,Pt/SiO2-Al2O3-15% CeO2表现出了最优氧化性能,其能在较宽温度范围内维持61%的NO2产率。CO-化学吸附结果表明,适量CeO2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CeO2改性后高分散的Pt颗粒的存在,X射线衍射(XRD)结果也说明CeO2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CeO2的添加增强了贵金属-载体间的相互作用,从而更利于PtOx与CeO2还原。总之,本文表明CeO2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。

关键词: CeO2表面改性柴油车氧化催化剂NO氧化表面Pt原子比例提高Pt-Ce相互作用    
Abstract:

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 C3H6, 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.

Key words: CeO2-modified catalysts    Diesel oxidation catalysts    NO oxidation    Increased surface Pt atomic ratio    Pt-Ce interaction
收稿日期: 2016-12-12 出版日期: 2017-03-29
中图分类号:  O643  
基金资助: The project was supported by the National Natural Science Foundation of China(21173153);National Hi-Tech Research and Development Program of China (863)(2015AA034603)
通讯作者: 王健礼,陈耀强     E-mail: wangjianli@scu.edu.cn;nic7501@scu.edu.cn
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引用本文:

黄于芬,张海龙,杨铮铮,赵明,黄木兰,梁艳丽,王健礼,陈耀强. CeO2的添加对柴油车氧化催化剂Pt/SiO2-Al2O3的NO氧化性能提高的影响[J]. 物理化学学报, 2017, 33(6): 1242-1252.

链接本文:

http://www.whxb.pku.edu.cn/CN/Y2017/V33/I6/1242

Fig 1  Comparison of single NO (a) oxidation activity and NO (b), CO (c) and C3H6 (d) oxidation activity in diesel simulated atmosphere over Pt/SiO2-Al2O3-wCe (w = 0%, 5%, 10%, 15%, 30%) catalysts (a) The atmosphere was mixed by 0.02% NO, 8% CO2, 10% O2, and N2 balance at a gas space velocity of 60000 h?1; (b, c, d) the simulative diesel exhaust gases contained amixture of 0.1% CO, 0.033% C3H6, 0.02% NO, 8% CO2, 10% O2, and N2 balance24 at a gas space velocity of 60000 h?1.
Fig 2  Catalytic performances (a, b, c, d) of Pt/SiO2-Al2O3-15% CeO2 samples at different reaction conditions The reaction conditions in different atmospheres were listed as follows: reaction condition of (a): 0.02% NO, 10% O2, 8% CO2, N2: balance, pulse 0.033% C3H6, 0.1% CO; Reaction condition of (b): 0.033% C3H6, 0.1% CO, 10% O2, 8% CO2, N2: balance, with or without 0.02% NO2; reaction condition of (c, d): 0.033% C3H6, 0.1% CO, 0.02% NO2, 8% CO2, N2: balance, with or without 10% O2; The catalytic activities were tested at the GHSV = 60000 h-1 and the catalyst was pre-treated at 550 ℃ for 3 h.
Fig 3  XRD patterns of SiO2-Al2O3 supports and Pt/SiO2-Al2O3-wCeO2 (w = 0%, 3%, 5%, 10%, 15%, 30%) catalysts ■ cubic CeO2, ▲ γ-Al2O3, ★ Pt (111)
CatalystsSBET/(m2 g?1)V/(cm3 g?1)dPt a/nmdPt b/nmDPt/nm
0% Ce152.54.927.126.512.4
5% Ce141.14.4??8.1
10% Ce134.14.4??6.9
15% Ce133.33.9?6.35.5
30% Ce118.83.1??6.0
Table 1  Textural and structural properties of Pt/SiO2-Al2O3-wCeO2 (w = 0%, 5%, 10%, 15%, 30%) catalysts
Fig 4  Relationship between dispersion and optimal NO conversion to NO2
Fig 5  H2-TPR profiles of SiO2-Al2O3, SiO2-Al2O3-15% CeO2 supports and Pt/SiO2-Al2O3-wCeO2 (w = 0, 15%) catalysts
Fig 6  The morphology, the metal particle size and High-Resolution TEM (HRTEM) of catalysts (a, b) TEM of Pt/SiO2-Al2O3; (c, d) TEM of Pt/SiO2-Al2O3-15% CeO2; (e, f) HRTEM of Pt/SiO2-Al2O3-15% CeO2. The Pt particle size distribution histograms were in the inset section.
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