Mechanistic insights into sulfation-induced deactivation of CoMn2O4/CeTiOx catalyst under low-temperature SCR conditions

doi:10.1016/S1872-2067(25)64781-4

Abstract

Abstract:

The problem of water and sulfur poisoning in flue gas atmosphere remains a significant obstacle for low-temperature deNO_x catalysts. This study investigated the sulfation mechanism of the CoMn₂O₄/CeTiO_x (CMCT) catalyst during the selective catalytic reduction of NO_x with NH₃ under conditions containing H₂O and SO₂ at 150 °C. Employing a comprehensive suite of time-resolved analysis and characterization techniques, the evolution of sulfate species was systematically categorized into three stages: initial rapid surface sulfate accumulation, the transformation of surface sulfates to bulk metal sulfates, and partial sulfates decomposition after the removal of H₂O and SO₂. These findings indicate that bulk metal sulfates irreversibly deactivate the catalyst by distorting active component lattices and consuming oxygen vacancies, whereas surface sulfates (including ammonium sulfates and surface-coordinated metal sulfates) cause reversible performance loss through decomposition. Furthermore, the competitive adsorption of H₂O and SO₂ significantly influences the catalytic efficiency, with H₂O suppressing SO₂ adsorption while simultaneously enhancing the formation of Brönsted acid sites. This research underscores the critical role of sulfate dynamics on catalyst performance, revealing the enhanced SO₂ resistance of the Eley-Rideal mechanism facilitated by the Ce-Ti support relative to the Langmuir-Hinshelwood pathway. Collectively, the study unravels the complex interplay of sulfate dynamics influencing catalyst performance and provides potential approaches to mitigate deactivation in demanding atmospheric conditions.

Key words: Selective catalytic reduction with NH₃, CoMn₂O₄/CeTiO_x, H₂O and SO₂ resistance, Surface sulfate, Bulk sulfate

Ning Luo, Fengyu Gao, Chengzhi Wang, Honghong Yi, Shunzheng Zhao, Yuansong Zhou, Shangfeng Du, Xiaolong Tang. Mechanistic insights into sulfation-induced deactivation of CoMn₂O₄/CeTiO_x catalyst under low-temperature SCR conditions[J]. Chinese Journal of Catalysis, 2025, 77: 70-86.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(25)64781-4

https://www.cjcatal.com/EN/Y2025/V77/I10/70

Figures/Tables 9

Fig. 1. (a) NH3-SCR stability test of CoMn2O4/CeTiOx catalyst. Reaction conditions: [NOx] = [NH3] = 500 × 10-6, [O2] = 8 vol%, [H2O] = 10 vol%, [SO2] = 100 × 10-6, N2 balanced, GHSV = 32000 h-1. (b) Comparison diagram of thermogravimetric analysis of catalyst at different reaction stages with the original catalyst. (c) The TG curves of catalyst after washing in different reaction stages. (d) The comparison of the mass loss over catalysts.

Fig. 2. Raman mapping spectrum (normalized, reference peak 350 cm-1), 2D mapping (normalized, reference peak 350 cm-1) and distribution of different characteristic peaks of catalysts at different reaction stages. (a) CMCT; (b) CMCT-F; (c) CMCT-D; (d) CMCT-T.

Table 1 Surface composition and N, S content of catalysts at different reaction stages.

Sample	Atomic concentration ^a (%)				Atomic concentration ^b (%)
Sample	Mn²⁺/Mn	Ce³⁺/Ce	Co²⁺/Co	O_vac/O_lat	N	S
CMCT	23.06	20.76	46.65	60.38	0	0
CMCT-F	31.74	29.10	53.81	49.35	2.13	1.41
CMCT-D	36.02	26.55	49.39	31.60	2.08	0.91
CMCT-T	37.41	28.56	46.23	34.90	1.80	1.15

Fig. 3. XPS spectra of catalysts at different reaction stages: Mn 2p (a), Ce 3d (b), and O 1s (c). (d) The average oxidation of Mn (data derived from the Mn 3s). (e) Contents of sulfate and ammonium detected by elemental analysis. (f) NOx conversion loss and S/M (M=metal) ratios during sulfation.

Fig. 4. (a) Adsorption performance of CMCT catalysts under different gas atmosphere, including NO + O2, NH3 and SO2 + O2. Reaction conditions: 50 °C, GHSV = 32000 h-1, [NOx] = [NH3] = 500 × 10-6, [SO2] = 100 × 10-6, [O2] = 8 vol%, N2 balanced. Relative uptake response (b) and selectivity co-efficient (c) of different gas combinations on different reaction stages of CMCT. Reaction conditions: 150 °C; adsorption time: 30 min; [NOx] = [NH3] = 500 × 10-6, [SO2] = 100 × 10-6, N2 balanced.

Fig. 5. In-situ DRIFT spectra and three-dimensional view of SO2 + O2 co-adsorption (a) and transient reactions between NH3 after pre-adsorbed SO2 + O2 (b) over CoMn2O4 (CM), CeTiOx (CT) and CoMn2O4/CeTiOx (CMCT). Reaction conditions: 150 °C; adsorption time: 30 min; [NOx] = [NH3] = 500 × 10-6, [SO2] = 100 × 10-6, [O2] = 8 vol%, N2 balanced.

Fig. 6. (a) Deconvolution of adsorption peaks for SO2 + O2, NH3, and NO + O2 on the CMCT catalyst, according to the characteristic peaks of its active components (CM) and support (CT). Reaction conditions: 150 °C; adsorption time: 30 min; [NOx] = [NH3] = 500 × 10-6, [SO2] = 100 × 10-6, [O2] = 8 vol%, balance gas N2. (b) The schematic diagram of the change of sulfate species over CMCT during the long-time NH3-SCR reaction.

Fig. 7. In-situ DRIFT spectra and three-dimensional view of the transient reactions at 150 °C between H2O/SO2/H2O + SO2 after pre-adsorbed NO2 + O2 + NH3 for 30 min as a function of time (a) and between NO + O2/NH3 after pre-adsorbed NO2 + O2 + NH3 + H2O + SO2 for 60 min as a function of time over (b) CoMn2O4 (CM), CeTiOx (CT) and CoMn2O4/CeTiOx (CMCT). Experimental conditions: [NO] = 500 × 10-6, [SO2] = 100 × 10-6, [H2O] = 10 vol%, [O2] = 8 vol% and N2 balanced. Contents of sulfate and ammonium detected by elemental analysis.

Fig. 8. (a) The schematic diagram of the change of sulfate species over CMCT during the long time NH3-SCR reaction. (b) Schematic diagram of the effect mechanism of the sulfates on SCR reaction over CMCT at different reaction stages.

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Mechanistic insights into sulfation-induced deactivation of CoMn₂O₄/CeTiO_x catalyst under low-temperature SCR conditions

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