Effect of CeO2 on Low-temperature Denitrification Performance of MnOx Catalysts and Its Mechanism

doi:10.15541/jim20250044

Abstract

Abstract:

Nitrogen oxides (NO_x), as main atmospheric pollutants in China, are usually removed through ammonia selective catalytic reduction (NH₃-SCR) technology to achieve ultra-low emissions. Low-temperature NH₃-SCR has gained much attention due to its low energy consumption and cost. However, MnO_x-based catalysts generally suffer from insufficient stability and are susceptible to SO₂ and H₂O poisoning at 120 ℃. To improve the denitrification performance of MnO_x-based catalysts under low temperature and lean flue gas conditions, CeO₂/MnO_x catalysts were prepared by precipitation-calcination decomposition method in this study. Influence of CeO₂ modification on structure, surface properties and low-temperature NH₃-SCR performance of catalyst was systematically studied. Combining first principles calculations, influence of CeO₂ modification on catalytic mechanism for reducing activation energy of the reaction was revealed at microscopic level. The results showed that addition of CeO₂ refined micro particle size of catalyst, reduced proportion of main crystalline phase MnO₂, significantly increased concentration of weak acid sites in the catalyst, augmented proportion of Mn³⁺/Mn and O_α/O, and improved surface acidity and redox performance of the catalyst. The prepared Mn10Ce3 and Mn10Ce5 catalysts achieved a NO conversion rate of over 98%, maintaining stability even at 120 ℃. Addition of CeO₂ dispersed the aggregated MnO_x and reduced concentration of Mn⁴⁺ distribution, which to some extent hindered excessive oxidation of NH₃ and NO by high valence Mn⁴⁺, thereby suppressing N₂O formation and improving N₂ selectivity of the catalyst. First principles calculations further confirmed that CeO₂ modification reduced the activation energy of various intermediate states in reaction pathway, lowering the reaction temperature and improving the low-temperature NH₃-SCR efficiency.

Key words: low-temperature ammonia selective catalytic reduction, CeO₂/MnO_x catalyst, reaction mechanism

CLC Number:

X701

WU Boyu, ZHANG Shengen, ZHANG Shengyang, LIU Bo, ZHANG Bolin. Effect of CeO₂ on Low-temperature Denitrification Performance of MnO_x Catalysts and Its Mechanism[J]. Journal of Inorganic Materials, 2026, 41(1): 87-95.

Figures/Tables 17

Fig. 1 XRD patterns of the prepared catalysts

Fig. 2 Raman spectra of the prepared catalysts

Fig. 3 SEM images of (a) Mn10, (b) Mn10Ce1, (c) Mn10Ce3, and (d) Mn10Ce5 catalysts

Fig. 4 (a) NH3-TPD and (b) NO-TPD profiles of the prepared catalysts

Fig. 5 High-resolution XPS spectra of (a) Mn2p, (b) Ce3d and (c) O1s of the prepared catalysts

Fig. 6 H2-TPR profiles of the prepared catalysts

Fig. 7 (a) NO conversion and (b) N2 selectivity of the prepared catalysts in the range of 90-150 ℃

Fig. 8 SO2 and H2O resistance of the prepared catalysts at 120 ℃

Table 1 NH3 adsorption energies at different sites on CeO2/MnO2 surface

Site	NH₃@O_l	NH₃@O_α
1	-1.28 eV	-1.61 eV
2	-1.53 eV	-1.97 eV
3	-1.60 eV	-2.06 eV
4	-1.10 eV	-1.84 eV

Fig. 9 NH3-SCR pathways on the surface of MnO2 and CeO2/MnO2

Fig. S1 (a) N2 adsorption-desorption isotherms and (b) corresponding BJH pore diameter distributions of the prepared catalysts

Fig. S2 (a) Optimal configuration of CeO2 dimer on MnO2 surface and (b) formation energy of CeO2/MnO2 model

Table S1 Speciﬁc surface area, pore volume and average pore size of the prepared catalysts

Catalyst	S_BET/(m²·g⁻¹)	Pore volume/ (cm³·g⁻¹)	Average pore size/nm
Mn10	34.7	0.078	7.9
Mn10Ce1	35.4	0.067	6.8
Mn10Ce3	37.3	0.074	7.2
Mn10Ce5	38.3	0.079	7.5

Table S2 Adsorption capacity for NH3 and NO of the prepared catalysts (μmol·g−1)

Catalyst	NH₃-TPD			NO-TPD
Catalyst	Peak I	Peak II	Total	Peak I	Peak II	Total
Mn10	64.4	35.3	99.7	1.9	0.4	2.3
Mn10Ce1	66.1	17.9	84.0	1.9	1.0	2.9
Mn10Ce3	72.6	45.0	117.6	2.3	1.9	4.2
Mn10Ce5	100.6	30.5	131.1	2.1	1.0	3.1

Table S3 Surface elements analysis of the prepared catalysts (%, atom fraction)

Catalyst	Mn	Ce	O	Mn³⁺/Mn	Ce³⁺/Ce	O_α/O
Mn10	36.4	-	63.6	19.4	-	26.4
Mn10Ce1	30.1	4.4	65.5	21.3	5.7	29.0
Mn10Ce3	21.9	11.9	66.2	22.4	7.9	35.9
Mn10Ce5	19.6	15.6	64.8	23.2	6.4	29.3

Table S4 H2 relative consumption of the prepared catalysts by H2-TPR test

Catalyst	Peak I	Peak II	Total
Mn10	3.3	16.4	19.7
Mn10Ce1	3.2	16.9	20.1
Mn10Ce3	4.4	15.2	19.6
Mn10Ce5	4.1	14.2	18.3

Table S5 Comparison of NH3-SCR performance of the samples prepared in this study with existing literature

Catalyst	NO conversion @120 ℃/%	T₉₀/℃	NO inlet/ppm
Mn10Ce3	99.1	110	100
Mn10Ce5	98.2	110	100
MnO_x-CeO₂^[S4]	-	120	400
NbmCeO_x^[S5]	-	200	1000
Mn-Ce/Al₂O₃^[S6]	~98	100	500
MnO_x-CeO₂-TiO₂^[S7]	~28	220	3000
CeO₂/Mn-Fe-O^[S8]	~98	-	500

References 30

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Effect of CeO₂ on Low-temperature Denitrification Performance of MnO_x Catalysts and Its Mechanism

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