CeO2 doping boosted low-temperature NH3-SCR activity of FeTiOx catalyst: A microstructure analysis and reaction mechanistic study

doi:10.1007/s11783-022-1539-2

Front. Environ. Sci. Eng.

2022, Vol. 16

Issue (5) : 60 https://doi.org/10.1007/s11783-022-1539-2

RESEARCH ARTICLE

CeO₂ doping boosted low-temperature NH₃-SCR activity of FeTiO_x catalyst: A microstructure analysis and reaction mechanistic study

Wei Tan^1,², Shaohua Xie¹, Wenpo Shan^3,⁴, Zhihua Lian^3,⁴, Lijuan Xie³, Annai Liu⁵, Fei Gao², Lin Dong², Hong He^3,⁴, Fudong Liu¹(

)

¹. Department of Civil, Environmental, and Construction Engineering, Catalysis Cluster for Renewable Energy and Chemical Transformations (REACT), NanoScience Technology Center (NSTC), University of Central Florida, Orlando, FL32816, USA
². Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Jiangsu Key Laboratory of Vehicle Emissions Control, School of Environment, Center of Modern Analysis, Nanjing University, Nanjing 210023, China
³. State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
⁴. Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
⁵. Institute of Engineering Technology, Sinopec Catalyst Co. Ltd., Sinopec Group, Beijing 101111, China

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Abstract

• CeO₂ doping significantly improved low-temperature NH₃-SCR activity on FeTiO_x.

• The crystallinity of FeTiO_x was decreased dramatically after CeO₂ doping.

• Unique Ce-O-Fe structure in FeCe_0.2TiO_x accounted for its superior redox property.

• Facile activation of NH₃ to-NH₂ on FeCe_0.2TiO_x promoted the DeNO_x efficiency.

FeTiO_x has been recognized as an environmental-friendly and cost-effective catalyst for selective catalytic reduction (SCR) of NO_x with NH₃. Aimed at further improving the low-temperature DeNO_x efficiency of FeTiO_x catalyst, a simple strategy of CeO₂ doping was proposed. The low-temperature (<250℃) NH₃-SCR activity of FeTiO_x catalyst could be dramatically enhanced by CeO₂ doping, and the optimal composition of the catalyst was confirmed as FeCe_0.2TiO_x, which performed a NO_x conversion of 90% at ca. 200℃. According to X-ray diffraction (XRD), Raman spectra and X-ray absorption fine structure spectroscopy (XAFS) analysis, FeCe_0.2TiO_x showed low crystallinity, with Fe and Ce species well mixed with each other. Based on the fitting results of extended X-ray absorption fine structure (EXAFS), a unique Ce-O-Fe structure was formed in FeCe_0.2TiO_x catalyst. The well improved specific surface area and the newly formed Ce-O-Fe structure dramatically contributed to the improvement of the redox property of FeCe_0.2TiO_x catalyst, which was well confirmed by H₂-temperature-programmed reduction (H₂-TPR) and in situ XAFS experiments. Such enhanced redox capability could benefit the activation of NO and NH₃ at low temperatures for NO_x removal. The detailed reaction mechanism study further suggested that the facile oxidative dehydrogenation of NH₃ to highly reactive-NH₂ played a key role in enhancing the low-temperature NH₃-SCR performance of FeCe_0.2TiO_x catalyst.

Keywords NH₃-SCR CeO₂ doping Low-temperature NO_x removal Improved redox property In situ XAFS analysis

Corresponding Author(s): Fudong Liu

Issue Date: 26 January 2022

Cite this article:

Wei Tan,Shaohua Xie,Wenpo Shan, et al. CeO₂ doping boosted low-temperature NH₃-SCR activity of FeTiO_x catalyst: A microstructure analysis and reaction mechanistic study[J]. Front. Environ. Sci. Eng., 2022, 16(5): 60.

URL:

https://academic.hep.com.cn/fese/EN/10.1007/s11783-022-1539-2
https://academic.hep.com.cn/fese/EN/Y2022/V16/I5/60

Fig.1 (a) The NH₃-SCR activity over FeTiO_x and FeCe_aTiO_x catalysts (a = 0.1, 0.2, 0.6, 1 and 1.6) under GHSV of 50000 h^-¹. (b) The NO_x conversion as a function of reaction time in NH₃-SCR reaction over FeCe_0.2TiO_x catalyst in the presence of 100 ppm SO₂ or/and 5% H₂O at 250℃ under the GHSV of 50000 h^-¹.

Fig.2 (a) XRD patterns and (b) Raman spectra for FeTiO_x and FeCe_aTiO_x catalysts with reference oxides.

Fig.3 (a) Normalized XANES spectra of Fe K-edge in Fe₂O₃, FeTiO_x and FeCe_aTiO_x catalysts, (b) Fourier transforms of filtered EXAFS oscillations k³χ(k) into R space for Fe K-edge in Fe₂O₃, FeTiO_x and FeCe_aTiO_x catalysts. (c) Normalized XANES spectra of Ce K-edge in CeO₂ and FeCe_aTiO_x catalysts, (d) Fourier transforms of filtered EXAFS oscillations k³χ(k) into R space for Ce K-edge in CeO₂ and FeCe_aTiO_x catalysts (the inserted figure was the inverse Fourier transformed EXAFS oscillations in FeCe_0.1TiO_x and FeCe_0.2TiO_x in the R range of ca. 2.3–3.2 Å, in which the dotted lines were related to the calculated EXAFS oscillations of Ce-O-Fe bond using FEFF8.4 code)。

Fig.4 (a) NH₃-TPD profiles for FeTiO_x and FeCe_0.2TiO_x catalysts; (b) In situ DRIFTS of NH₃ adsorption on FeTiO_x and FeCe_0.2TiO_x catalysts at 150℃ collected in N₂ flow.

Fig.5 H₂-TPR profiles for FeTiO_x and FeCe_0.2TiO_x catalysts, with TiO₂, CeO₂ and Fe₂O₃ as reference samples.

Fig.6 The normalized in situ Fe K-edge XANES for (a) FeTiO_x and (b) FeCe_0.2TiO_x catalysts in the H₂-TPR process from room temperature to 900℃ (the inserted figures showed the normalized in situ Fe K-edge XANES with an interval of 50℃ for better discrimination); In situ EXAFS spectra of Fe K-edge for (c) FeTiO_x and (d) FeCe_0.2TiO_x catalysts during the H₂-TPR process.

Fig.7 In situ DRIFTS of (a) NO+ O₂ reacting with pre-adsorbed NH₃ species; (b) NH₃ reacting with pre-adsorbed NO_x species; (c) NH₃-SCR reaction at 150℃ over FeTiO_x. The FTIR spectra were collected in varied reactant flow according to the needs of the experiments.

Fig.8 In situ DRIFTS of (a) NO+ O₂ reacting with pre-adsorbed NH₃ species; (b) NH₃ reacting with pre-adsorbed NO_x species; (c) NH₃-SCR reaction at 150℃ over FeCe_0.2TiO_x. The FTIR spectra were collected in varied reactant flow according to the needs of the experiments.

Fig.9 (a) In situ DRIFTS of NH₃-SCR reaction on FeTiO_x and FeCe_0.2TiO_x at 150℃ collected in the NH₃-SCR reaction flow. (b) The scheme of the reaction pathway on FeTiO_x and FeCe_0.2TiO_x at 150℃.

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