物理化学学报 >> 2019, Vol. 35 >> Issue (4): 422-430.doi: 10.3866/PKU.WHXB201805301

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不同组成和结构LaMnO3钙钛矿负载Au催化剂的CO氧化活性

何成欢,郭杨龙,郭耘,王筠松,王丽,詹望成*()   

  • 收稿日期:2018-04-25 发布日期:2018-09-13
  • 通讯作者: 詹望成 E-mail:zhanwc@ecust.edu.cn
  • 基金资助:
    国家自然科学基金(21571061);国家重点研发计划(2016yfc0204300)

Catalytic Activity of Au Nanoparticles Supported on LaMnO3 Perovskite with Different Composition and Structure

Chenghuan HE,Yanglong GUO,Yun GUO,Yunsong WANG,Li WANG,Wangcheng ZHAN*()   

  • Received:2018-04-25 Published:2018-09-13
  • Contact: Wangcheng ZHAN E-mail:zhanwc@ecust.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21571061);the National Key Research and Development Program of China(2016yfc0204300)

摘要:

采用乙二醇溶胶-凝胶法制备了计量比LaMnO3和非计量比LaMn1.2O3钙钛矿,并利用稀硝酸处理LaMnO3制备得到LaMnO3-AE,然后采用沉积沉淀法制备钙钛矿负载Au催化剂,以考察载体的结构和性质对Au的热稳定性以及催化剂活性的影响。通过X射线衍射(XRD)、透射电镜(TEM)、X射线光电子能谱(XPS)和H2程序升温还原(H2-TPR)等表征,发现LaMnO3和LaMn1.2O3钙钛矿载体虽然有利于Au的分散,但是Au的热稳定性相对较差。相反,经稀硝酸刻蚀的LaMnO3钙钛矿(LaMnO3-AE)不利于Au的分散,但是有利于提高Au的热稳定性。在CO氧化反应中,当催化剂在低于500 ℃焙烧时,LaMn1.2O3钙钛矿负载Au催化剂的活性要显著高于LaMnO3和LaMnO3-AE负载Au催化剂的活性,而当催化剂焙烧温度升高至700 ℃以上时,LaMnO3-AE负载Au催化剂却要显著优于LaMnO3和LaMn1.2O3钙钛矿负载Au催化剂的活性。

关键词: 钙钛矿, 表面结构, Au纳米颗粒, CO氧化, 酸刻蚀

Abstract:

Perovskite is widely used as catalyst supports because of its flexible composition, good redox performance, and excellent thermal stability. However, the use of perovskite oxides as catalyst supports has two disadvantages: low surface area due to synthesizing the perovskite structure at high temperatures, and native perovskite surfaces preferentially have A-sites instead of catalytically active sites. On the other hand, interaction between the support and metal affects the size and valence state of noble metals. Therefore, perovskite oxides with different structures were prepared and were used to support Au catalysts, in order to obtain excellent catalytic activity and high stability. Specifically, stoichiometric LaMnO3 and nonstoichiometric LaMn1.2O3 perovskites were prepared by the ethylene glycol sol-gel method, and then the LaMnO3-AE oxide was prepared by treating LaMnO3 perovskite with dilute nitric acid. The perovskite-supported Au catalyst was prepared by the deposition precipitation method and its catalytic activity for CO oxidation was evaluated. Using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR), it was found that LaMnO3 and LaMn1.2O3 perovskite carriers were beneficial for the dispersion of Au; however, the Au nanoparticle size significantly increased with increasing calcination temperature, indicating poor Au thermal stability. In contrast, LaMnO3 perovskite (LaMnO3-AE) etched by nitric acid is not conducive to dispersion of Au, but it is beneficial for improving the thermal stability of Au. Au was always maintained in the zero-valence state after calcination at different temperature. H2-TPR results revealed that the reducibility of the catalysts changed largely after thermal treatment at high temperatures, and was mainly influenced by the agglomeration of Au nanoparticles. Although the reducibility of the Au/LaMnO3-AE catalyst calcined at 250 ℃ is lower than that of Au/LaMn1.2O3 and Au/LaMnO3 catalysts calcined at the same temperature, the former exhibited higher reducibility when the catalyst was calcined at high temperatures (500 and 900 ℃). In the CO oxidation reaction, the catalytic activity of all the prepared catalysts decreased when the calcination temperature was increased from 250 to 500, 700, and 900 ℃. However, the catalytic activity of the Au/LaMn1.2O3 catalyst was significantly higher than those of LaMnO3- and LaMnO3-AE-supported Au catalyst, when calcination temperature was below 500 ℃, while the activity of the Au/LaMnO3-AE catalyst was significantly higher than those of the Au/LaMnO3 and Au/LaMn1.2O3 catalysts when the calcination temperature was more than 700 ℃. As shown in characterization results, after the catalyst was calcined at high temperatures (700 and 900 ℃), the Au nanoparticle size on the Au/LaMnO3-AE catalyst was lower than those on Au/LaMnO3 and Au/LaMn1.2O3 catalysts, leading to high reducibility and catalytic activity of the Au/LaMnO3-AE catalyst. The Au/LaMnO3-AE catalyst also exhibited high stability in CO oxidation. The catalytic activity of the Au/LaMnO3-AE catalyst can be maintained for 20 h at 130 ℃.

Key words: Perovskite, Surface structure, Au nanoparticle, CO oxidation, Acid etching

MSC2000: 

  • O643