English

Catalytic Oxidation of Toluene Over Potassium Modified Mn/Ce_0.65Zr_0.35O₂ Catalyst

• Lai Xiaoxiao ^1, ,
• Feng Jie ^2, ,
• Zhou Xiaoying ^1, ,
• Hou Zhongyan ^1, ,
• Lin Tao ^{1, ,} ,
• Chen Yaoqiang ^{1,3, ,}

• 1.

  College of Chemistry, Sichuan University, Chengdu 610064, P. R. China

• 2.

  College of Chemical Engineering, Sichuan University, Chengdu 610064, P. R. China

• 3.

  Sichuan Provincial Environmental Catalytic Material Engineering Technology Center, Chengdu 610064, P. R. China

Corresponding author: Lin Tao, lintaochem@scu.edu.cn Chen Yaoqiang, chenyaoqiang@scu.edu.cn

• Received Date: 13 May 2019
  Accepted Date: 02 July 2019
  Revised Date: 27 June 2019
  Available Online: 15 August 2020
• Fund Project:

  The research was supported by National Key Research and Development Program of China (2016YFC0204901)

  National Key Research and Development Program of China 2016YFC0204901

Abstract: Volatile organic compounds (VOCs) are both harmful to human health and the environment; however, catalytic combustion offers a promising method for VOC purification because of its high efficiency without secondary pollution. Although manganese-based catalysts have been well studied for VOC catalytic oxidation, their catalytic activity at low temperature must be improved. Alkali metals as promoters have the potential to modulate the electronic and structural properties of the catalysts, improving their catalytic activity. Herein, a Ce_0.65Zr_0.35O₂ support was prepared by co-precipitation and MnO_x/Ce_0.65Zr_0.35O₂ catalysts were obtained through the incipient-wetness impregnation method. The catalytic properties of K-modified MnO_x/Ce_0.65Zr_0.35O₂ for toluene oxidation with different molar ratios of K/Mn were investigated. In addition, the catalysts were characterized by XRD, UV/visible Raman, Hydrogen temperature program reduction (H₂-TPR), Oxygen temperature programmed desorption (O₂-TPD), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance FTIR spectroscopy (DRIFTS) experiments. The results showed that alkali metal doping with K significantly improved the catalytic activity. In particular, when the molar ratio of K/Mn was 0.2, the monolith catalyst Mn/Ce_0.65Zr_0.35O₂-K-0.2 exhibited the best performance with the lowest complete conversion temperature T₉₀ of 242 ℃ at a GHSV of 12000 h⁻¹. The XRD results suggested that MnO_x was uniformly distributed on the surface of the catalyst and that Mn⁴⁺ partially reduced to Mn³⁺ on the addition of K. The Raman spectrum demonstrated that with increasing K content, both the β- and α-MnO₂ phases coexisted on the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst, increasing the number of surface defect sites. The H₂-TPR experiment results confirmed that Mn/Ce_0.65Zr_0.35O₂-K-0.2 exhibited the lowest reduction temperature and good reducibility. From the O₂-TPD experiments, it was clear that Mn/Ce_0.65Zr_0.35O₂-K-0.2 contained the most surface adsorbed oxygen species and excellent lattice oxygen mobility, which benefitted the toluene oxidation activity. In addition, the XPS results suggested that the content of surface adsorbed oxygen species of the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst was the highest among all the tested samples. In addition, toluene-TPSR in N₂ as measured by in situ DRIFTs analysis demonstrated that available lattice oxygen was present in the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst. Therefore, the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst exhibited the best redox properties and oxygen mobility of the prepared samples and showed excellent activity toward toluene oxidation. Therefore, it was concluded that the addition of an appropriate amount of K improved the redox performance of the catalyst and increased the number of surface defect sites and mobility of the lattice oxygen of the catalyst as well as the concentration of the surface active oxygen species, thereby significantly improving catalytic ability.

Key words:
• Toluene
•  /  Catalytic oxidation
•  /  Potassium
•  /  Ce_0.65Zr_0.35O₂
•  /  Manganese oxide

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