物理化学学报

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高分散还原态Pt基催化剂的制备及其NO氧化的催化性能

丁心湄1, 梁艳丽2, 张海龙3, 赵明1, 王健礼1, 陈耀强1   

  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 四川大学高分子材料工程国家重点实验室, 成都 610064;
    3 厦门大学化学与化学工程学院, 厦门 361005
  • 收稿日期:2020-05-05 修回日期:2020-06-03 录用日期:2020-06-16 发布日期:2020-06-19
  • 通讯作者: 赵明, 王健礼 E-mail:zhaoming@scu.edu.cn;wangjianli@scu.edu.cn
  • 基金资助:
    国家自然科学基金(21972098)资助项目

Preparation of Reduced Pt-Based Catalysts with High Dispersion and Their Catalytic Performances for NO Oxidation

Xinmei Ding1, Yanli Liang2, Hailong Zhang3, Ming Zhao1, Jianli Wang1, Yaoqiang Chen1   

  1. 1 Key Laboratory of Green Chemistry & Technology of the Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, P. R. China;
    2 State Key Laboratory of Polymer Materials Engineering of China (Sichuan University), Polymer Research Institute of Sichuan University, Chengdu 610064, P. R. China;
    3 Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian Province, P. R. China
  • Received:2020-05-05 Revised:2020-06-03 Accepted:2020-06-16 Published:2020-06-19
  • Supported by:
    This work is financially supported by the National Nature Science Foundation of China (21972098).

摘要: Pt0被认为是NO氧化的活性物种,而催化剂的制备方法对活性物种的含量起着决定性作用。本文采用非惰性气氛保护的改性醇还原-浸渍法(MARI)合成了高分散高Pt0含量的1% (w, 质量分数) Pt/SiO2―Al2O3催化剂(MA-Pt/SA)。X射线粉末衍射(XRD)、CO-漫反射傅里叶变换红外吸收光谱(CO-DRIFTS)和透射电镜(TEM)表征证实在550 °C焙烧3 h后催化剂的Pt颗粒仅有3.8 nm。同时,X射线光电子能谱(XPS)和H2-程序升温还原(H2-TPR)结果表明催化剂具有高Pt0含量(60.3%)。模拟柴油车尾气气氛进行活性测试,并与传统浸渍法制备的1%(w) Pt/SiO2―Al2O3催化剂(C-Pt/SA)对比,结果显示MA-Pt/SA具有优异的催化氧化性能,其NO最大转化率高达74%,比C-Pt/SA的NO转化率高了23%。经670 °C高温老化15 h后,老化的MA-Pt/SA的NO转化率仍然高达69%。此外NO + O2共吸附原位漫反射傅里叶变换红外吸收光谱(in situ DRIFTS of NO + O2 co-adsorption)表明高的Pt分散度和高Pt0含量能够促进中间物种桥式硝酸盐的生成及分解,进而导致了优异的NO氧化活性。最后,利用同样方法将Pt的负载量降低至0.5%(w)制备催化剂,NO转化率仍达64%。这种制备方法能够获得低贵金属高性能的Pt基催化剂。

关键词: 柴油车氧化催化剂, 改性的醇还原-浸渍法, NO氧化, 高性能Pt基催化剂, 低Pt含量

Abstract: Pt-based catalysts are widely used in diesel oxidation catalyst (DOC) units, primarily to oxidize the harmful HC, CO, and NO emissions. Notably, NO2 produced from NO oxidation is beneficial for low-temperature activity in NH3-SCR and promotes soot oxidation in diesel particulate filters (DPF).Thus, the conversion of NO is an important parameter for determining the performance of DOCs. Considering the increasingly stringent emission regulations and the economic effectiveness, preparation of low-cost and highly active Pt-based catalysts is indispensable. Generally, the Pt0 content is crucial as it is an active component of DOCs. Small Pt size is beneficial for improving the catalytic activity. In this study, we applied a modified alcohol reduction-impregnation (MARI) method to synthesize highly active 1% (w, mass fraction) Pt/SiO2―Al2O3 (denoted as MA-Pt/SA) catalyst. Meanwhile, using the conventional impregnation method, we prepared the Pt/SiO2―Al2O3 catalyst with the same Pt loading (denoted as C-Pt/SA) as a reference sample. X-ray photoelectron spectroscopy (XPS) and hydrogen temperature program reduction (H2-TPR) analyses proved that the MARI method could produce Pt catalysts with higher Pt0 content. Pt0 content in MA-Pt/SA was ~60.3% while that in C-Pt/SA was only ~23.1%. X-ray diffraction (XRD), CO-diffuse reflectance infrared fourier transform spectroscopy (CO-DRIFTS), and transmission electron microscopy (TEM) characterization confirmed that the Pt particle size is much smaller over MA-Pt/SA as compared to that over C-Pt/SA. Performance evaluation of MA-Pt/SA and C-Pt/SA was conducted in a simulated diesel atmosphere. The results showed that the maximum NO conversion into NO2 over MA-Pt/SA is 74% and 68% in the absence and presence of H2O, respectively, which were much higher than those over C-Pt/SA (42% and 51% NO conversion with and without H2O, respectively). Furthermore, the temperature for 30% NO conversion over MA-Pt/SA (218 °C) markedly decreased as compared to that over C-Pt/SA (248 °C), indicating the excellent low temperature activity. After the aging treatment with reaction gas at high temperatures, aged MA-Pt/SA maintained 69% NO conversion while aged C-Pt/SA showed only 41% NO conversion. In addition, in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) of NO + O2 co-adsorption suggested that higher Pt dispersion and higher Pt0 content over MA-Pt/SA could facilitate the formation of bridging nitrates as intermediate species in NO oxidation at lower temperatures and could also facilitate their rapid decomposition (or desorption) at higher temperatures, thus imparting a high catalytic activity. Furthermore, a decrease in the Pt loading to 0.5% (w) resulted in a maximum NO conversion of 64% via the MARI method, suggesting a higher catalytic activity compared to that of C-Pt/SA with 1% (w) Pt loading. This work provides a method to prepare highly active Pt-based catalysts with low noble loading.

Key words: DOC, Modified alcohol reduction-impregnation method, NO oxidation, High-performing Pt catalyst, Low Pt loading

MSC2000: 

  • O643