Comprehensive understanding of the superior performance of Sm-modified Fe2O3 catalysts with regard to NO conversion and H2O/SO2 resistance in the NH3-SCR reaction

doi:10.1016/S1872-2067(20)63666-X

Abstract

Abstract:

Abstract:Sm-doped Fe2O3 catalysts,with a homogeneous distribution of Sm in Fe2O3 nanoparticles,were synthesized using a citric acid-assisted sol-gel method. Kinetic studies show that the reaction rate for NOx reduction using the optimal catalyst (0.06 mol% doping of Sm in Fe2O3) was nearly 11 times higher than that for pure Fe2O3,when calculated based on specific surface area. Furthermore,the Fe0.94Sm0.06Ox catalyst maintains > 83% NOx conversion for 168 h at a high space velocity in the presence of SO2 and H2O at 250 °C. A substantial amount of surface-adsorbed oxygen was generated on the surface of Fe0.94Sm0.06Ox,which promoted NO oxidation and the subsequent fast reaction between NOx and NH3. The adsorption and activation of NH3 was also enhanced by Sm doping. In addition,Sm doping facilitated the decomposition of NH4HSO4 on the surface of Fe0.94Sm0.06Ox,resulting in its high activity and stability in the presence of SO2 + H2O.

Key words: NH3-SCR, NOx conversion, Sm-doped Fe2O3, SO2 and H2O tolerance, 168 h test

Chuanzhi Sun, Wei Chen, Xuanxuan Jia, Annai Liu, Fei Gao, Shuai Feng, Lin Dong. Comprehensive understanding of the superior performance of Sm-modified Fe₂O₃ catalysts with regard to NO conversion and H₂O/SO₂ resistance in the NH₃-SCR reaction[J]. Chinese Journal of Catalysis, 2021, 42(3): 417-430.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(20)63666-X

https://www.cjcatal.com/EN/Y2021/V42/I3/417

Figures/Tables 15

Fig. 1. NOx conversion of the synthesized catalysts as a function of reaction temperature (a) and the influence of 200 × 10-6 SO2 and 5 vol% H2O on Fe0.94Sm0.06Ox for the NH3-SCR reaction at 250 °C (b).

Fig. 2. Reaction rates based on the specific area (a),mass (b),and apparent activation energies (c) of the NH3-SCR reactions over the Fe2O3 and Fe0.94Sm0.06Ox catalysts.

Fig. 3. XRD patterns of the synthesized catalysts.

Fig. 4. TEM images of Fe2O3 (a) and Fe0.94Sm0.06Ox (c),HR-TEM images of Fe2O3 (b) and Fe0.94Sm0.06Ox (d),and HAADF image (e) and EDS mappings (f-h) of Fe0.94Sm0.06Ox.

Table 1 Surface compositions of the Fe2O3,Sm2O3 and Fe0.94Sm0.06Ox catalysts.

Sample	Fe³⁺/Fe²⁺	Sm³⁺/Sm²⁺	O_α/(O_α+ O_β) (%)
Fe₂O₃	1.03	—	43.7
Sm₂O₃	—	2.50	—
Fe_0.94Sm_0.06O_x	1.65	2.20	50.8
Fe₂O₃-U	1.84	—	53.6
Fe_0.94Sm_0.06O_x-U	3.04	2.00	58.7

Fig. 5. XPS spectra of α-Fe2O3,Fe0.94Sm0.06Ox,and Sm2O3 over the Fe 2p (a),Sm 3d (b),and O 1s (c) spectral regions.

Fig. 6. Optimized Sm-doped Fe2O3 (001) model from the DFT calculations: (a) top view and (c) side view. Differential charge densities of the Sm-doped Fe2O3 (001) model: (b) top view and (d) side view. The blue and yellow colors indicate the loss and gain of electrons,respectively.

Fig.7. (a) H2-TPR profiles of the synthesized catalysts at 200-400 °C; (b) the relationship between the numbers of different acid sites and NO conversion.

Table 2 Peak area of the samples at different reduction temperatures.

Sample	Peak area (a.u.)
Sample	~322 °C	~384 °C
Fe₂O₃	—	582.0
Fe_0.98Sm_0.02O_x	87.9	278.1
Fe_0.96Sm_0.04O_x	186.5	86.3
Fe_0.94Sm_0.06O_x	268.0	122.4
Fe_0.92Sm_0.08O_x	284.9	96.2
Fe_0.90Sm_0.10O_x	154.6	104.7

Fig. 8. In situ DRIFTS spectra of NH3 adsorption-desorption over the Fe2O3 (a),Sm2O3 (b),and Fe0.94Sm0.06Ox (c) catalysts; in situ DRIFTS spectra of NO + O2 adsorption-desorption over the Fe2O3 (d),Sm2O3 (e),and Fe0.94Sm0.06Ox (f) catalysts as the temperature increases from 50 to 350 °C.

Fig. 9. In situ DRIFTS spectra of the interaction between NO + O2 and adsorbed NH3 over the Fe2O3 (a) and Fe0.94Sm0.06Ox (b) catalysts; in situ DRIFTS spectra of the interaction between NH3 and adsorbed NO + O2 over the Fe2O3 (c) and Fe0.94Sm0.06Ox (d) catalysts at 200 °C as a function of time.

Fig. 10. TG curves of the Fe2O3 (a) and Fe0.94Sm0.06Ox (b) catalysts.

Fig. 11. XPS spectra of α-Fe2O3-U and Fe0.94Sm0.06Ox-U over the Fe 2p,Sm 3d,O 1s,and S 2p spectral regions.

Fig. 12. HAADF image and EDS mappings of Fe2O3-U (a-d) and Fe0.94Sm0.06Ox-U (e-i).

Fig. 13. In situ DRIFTS SO2 + O2 adsorption spectra over Fe2O3 (a) and Fe0.94Sm0.06Ox (b) at 250 °C as a function of time.

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Comprehensive understanding of the superior performance of Sm-modified Fe₂O₃ catalysts with regard to NO conversion and H₂O/SO₂ resistance in the NH₃-SCR reaction

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