English

Effect of Potassium on the Performance of a CuSO₄/TiO₂ Catalyst Used in the Selective Catalytic Reduction of NO_x by NH₃

• Yanke Yu ^1, ,
• Mengqiao Geng ^1, ,
• Desheng Wei ^1, ,
• Chi He ^{1, 2, 3, ,}

• 1.

  Department of Environmental Science and Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China

• 2.

  State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China

• 3.

  National Engineering Laboratory for VOCs Pollution Control Material & Technology, University of Chinese Academy of Sciences, Beijing 101408, China

Corresponding author: Chi He, chi_he@xjtu.edu.cn

• Received Date: 22 June 2022
  Accepted Date: 13 July 2022
  Revised Date: 12 July 2022
  Available Online: 15 April 2023
• Fund Project:

Abstract: Owing to its renewability, abundance, and low environmental impact, biomass is considered to be a viable eco-friendly fuel. Various biofuel-fired power plants have been built worldwide to reduce carbon emissions. Potassium (K) is a typical impurity in the flue gas from biofuel combustion that can deactivate the catalyst used in the selective catalytic reduction of NO_x by ammonia (NH₃-SCR). CuSO₄/TiO₂, with excellent sulfur dioxide tolerance, is thought to be a promising vanadium-free catalyst for NH₃-SCR; however, the influence of K on the CuSO₄/TiO₂ catalyst is still unknown. Therefore, in this study, the effect of K on the NH₃-SCR performance of CuSO₄/TiO₂ were investigated and compared with the effect on the performance of the commercial V₂O₅-WO₃/TiO₂ (VWTi) catalyst. K-poisoned catalysts were prepared via wet impregnation using potassium acetate as the K source. Nitrogen (N₂) adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH₃-temperature programmed desorption (NH₃-TPD), H₂-temperature programmed reduction (H₂-TPR), and in situ diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) were used to characterize the prepared catalysts. The NO_x conversion over CuSO₄/TiO₂ with 1.0% (w) K was 92.1% (at 350 ℃), which was higher than the conversion (75.1%) achieved over the commercial VWTi catalyst with the same K content. The XRD, XPS, and H₂-TPR results suggested that K reacted with the CuSO₄ in the CuSO₄/TiO₂ catalyst to form CuO and K₂SO₄. The presence of CuO enhanced the oxidation of NH₃ to N₂O, NO, and NO₂ during NH₃-SCR, thereby decreasing the NO_x conversion and N₂ selectivity over CuSO₄/TiO₂. Moreover, based on the results from NH₃-TPD and in situ DRIFTS of NH₃ adsorption, it can be concluded that the Brønsted acid sites (S-OH) were poisoned by K, which restrained the adsorption of NH₃ on CuSO₄/TiO₂. Additionally, the high K content altered the pore structure of the catalyst, leading to a decrease in the specific surface area. However, according to the in situ DRIFTS results, NH₃-SCR over K-poisoned CuSO₄/TiO₂ still followed the Eley-Rideal mechanism: First, NH₃ was adsorbed on the Lewis and Brønsted acid sites of the catalyst, and then gaseous NO and O₂ reacted with the adsorbed NH₃/NH₄⁺ on the acid sites, resulting in the formation of N₂ and H₂O. Notably, the abundance of acid sites and surface-adsorbed oxygen species on CuSO₄/TiO₂ could be the main reason for its higher resistance to K-poisoning. In conclusion, our current findings suggested that CuSO₄/TiO₂ might be a suitable NH₃-SCR catalyst for use in the flue gas streams from biofuel-fired power plants.

Key words:
• NH₃-SCR catalysts
•  /  NO_x
•  /  Brønsted acid sites
•  /  CuO
•  /  biofuel-fired power plants

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