物理化学学报 >> 1999, Vol. 15 >> Issue (08): 721-725.doi: 10.3866/PKU.WHXB19990811

研究论文 上一篇    下一篇

负载型La0.8Sr0.2MnO3燃烧催化剂的载体效应

孙燕华, 沈岳年, 贾美林, 胡瑞生   

  1. 内蒙古大学化学系,呼和浩特 010021
  • 收稿日期:1998-10-16 修回日期:1999-02-22 发布日期:1999-08-15
  • 通讯作者: 沈岳年

The Effects of Support on Loaded Combustion Catalyst of La0.8Sr0.2MnO3

Sun Yan-Hua, Shen Yue-Nian, Jia Mei-Lin, Hu Rui-Sheng   

  1. Department of Chemistry,Neimonglo University,Hohhot 010021
  • Received:1998-10-16 Revised:1999-02-22 Published:1999-08-15
  • Contact: Shen Yue-Nian

摘要:

用浸渍法制备负载型La0.8Sr0.2MnO3燃烧催化剂,比较了γ-Al2O3、α-AI2O3、堇青石(2MgO•2Al2O3、5SiO2)和ZrO2四种载体的负载效果.用XRD,DPR着重研究了γ-Al2O3载体上由于负载量不同、焙烧温度不同引起的催化剂物相变化和二甲苯完全氧化的催化活性变化.

关键词: 燃烧催化剂, La0.8Sr0.2MnO3, 二甲苯完全氧化, 载体效应

Abstract:

Combustion catalysts La0.8Sr0.2MnO3 supported on γ-Al2O3, α-Al2O3, cordierite (2MgO•2Al2O3•5SiO2) and ZrO2 were compared. Further investigation was focused on LSM/ γ-Al2O3 catalyst. It was observed that LSM/γ-Al2O3 catalyst loaded with 20% (mass fraction) LSM (La0.8Sr0.2MnO3 or corresponding oxides), heated at 750℃ or above, perovskite-type oxides were found by XRD examination, whereas, the same catalyst loaded with 10% or less LSM, perovskite oxides were absent, calcination temperature about 750℃ is necessary for the formation of perovskite structure in LSM/γ-Al2O3 catalysts. High activity of complete oxidation of xylen will be obtained when perovskite-type oxides.
Investigation of TPR showed that neat LSM or LSM/γ-Al2O3(20%) was reduced by H2-N2 mixed gas. Two degradation processes took place. In the first, reduced temperature peak was about 350 - 450℃. If reduction ended at 400℃, perovskite structure was retained, which may be due to the reduction of Mn3+to Mn2+ on the surface of LSM only. In the second process, perovskite structure was destroied, and La2O3, Mn2O3, Mn - Sr - O oxides could be obtained, which took place in the temperature range 685 - 750℃ and ended at 800℃. This was proved by TPR experiments (Fig. 3, 5) and XRD patterns (Fig. 4)
Catalysts LSM/γ-Al2O3(10% or 20%) heated at 500℃ have only one TPR peak, i. e. lower temperature peak. This is due to the absence of perovskite-type oxides in the catalysts. However, neat LSM or LSM/γ-Al2O3(20%) heated 750℃ or above, not only the first low temperature TPR peak but also the second peak, which is contributed by the perovskite-type oxides in these catalysts appeared. Therefore, the second TPR peak, i. e. the higher temperatue peak is a characteristic peak for perovskite-type oxides in the reduced process. When LSM/ γ-Al2O3 (10%) catalys is heated at 750℃, no perovskite-type oxides were detected by XRD, and the second reduction peak was absent also in TPR process. \
The order of the second reduction peak temperature(characteristic peak of perovskite - type ox- ides) is: neat LSM(750℃)> LSM/γ-Al2O3 20% (685-698℃) -deposited LSM/γ-Al2O3 (698℃) > LSM/γ-Al2O3 15% (677 - 680℃) >(LSM/γ-AL2O3 10% 620 - 630℃, for Mn - Al - O medium oxides on surface). It is correleted with the increasing of the effect of support sequentially.
When LSM/γ-Al2O3 catalysts were heated at 900℃, more stable phase, spinel MnAl2O4 appeared, which could be proved by TPR of model catalyst MnAl2O4/γ-Al2O3.

Key words: Combustion catalyst, La0.8Sr0.2MnO3, Complete oxidation of xylene, Effects of support