Simulation and experimental study on modification of water and sulfur resistance by Mn-based denitration catalyst

doi:10.11949/0438-1157.20190690

Abstract

Abstract:

To investigate the effect of ZSM-5 zeolite as carrier and Ce doping on the low temperature denitrification activity and water/sulfur resistance of the catalyst, the effects of carrier type and Ce doping on the performance of the catalyst were studied by molecular dynamics simulation and experimental research. Molecular dynamics simulations showed that ZSM-5 zeolite as a carrier significantly inhibited the adsorption of H₂O on its surface compared with γ-Al₂O₃. Adding Ce to the active component not only inhibited the adsorption of H₂O on its surface, but also mitigated the poisoning effect of SO₂ on the catalyst. The experimental study found that Mn-Fe-Ce/ZSM-5 has better denitration activity under low temperature and water/sulfur resistance. The addition of Ce has a positive effect on improving the low temperature activity and water/sulfur resistance of the catalyst. ZSM-5 zeolite as carriers also play an important role in improving the water resistance of the catalyst. The SEM, XRD, BET, TG-DTG and other characterization methods and BaCl₂ bubbling experiments were carried out to analyze the mechanisms for the improvement of sulfur resistance of Mn-Fe-Ce/ZSM-5 catalyst. It was found that the addition of Ce increased the oxygen storage and oxygen release capacity of the catalyst. Oxidation of SO₂ in the flue gas to SO₃ avoids the reaction of SO₂ with the active component, so that the active component on the surface of the catalyst is not destroyed, and the catalytic reaction performance of the catalyst is ensured.

Key words: low temperature denitration, Mn-based catalyst, selective catalytic reduction, molecular simulation, water/sulfur resistance

摘要：

为考察ZSM-5分子筛作载体和Ce掺杂对催化剂低温脱硝活性及抗水抗硫性的影响，通过分子动力学模拟和实验研究的手段研究了载体类型、掺杂Ce对催化剂性能的影响。分子动力学模拟发现，ZSM-5分子筛作载体较γ-Al₂O₃明显抑制H₂O在其表面的吸附，在活性组分中添加Ce既抑制H₂O在其表面的吸附，又减轻SO₂对催化剂的毒化作用。实验研究发现，Mn-Fe-Ce/ZSM-5催化剂性能更优，Ce的添加对提高催化剂的低温脱硝活性和抗水抗硫性能具有明显的积极作用，ZSM-5分子筛作为载体也对提高催化剂抗水性能起到重要作用。通过SEM、XRD、BET、TG-DTG等表征手段和BaCl₂鼓泡实验对Mn-Fe-Ce/ZSM-5催化剂抗硫性提高的原因分析发现，添加Ce使催化剂储氧释氧能力提高，将烟气中的SO₂氧化为SO₃并被烟气携带，避免了SO₂与催化剂活性组分的反应，则催化剂表面的活性组分不被破坏，保证了催化剂的催化反应性能。

关键词: 低温脱硝, 锰基催化剂, 选择催化还原, 分子模拟, 抗水抗硫性

CLC Number:

TQ 534.9

Jinyu WANG, Huaizhi ZHU, Zewen AN, Jian GONG, Cuiping WANG. Simulation and experimental study on modification of water and sulfur resistance by Mn-based denitration catalyst[J]. CIESC Journal, 2019, 70(12): 4635-4644.

王金玉, 朱怀志, 安泽文, 巩建, 王翠苹. Mn基脱硝催化剂抗水抗硫改性的模拟与实验研究[J]. 化工学报, 2019, 70(12): 4635-4644.

Figures/Tables 19

Fig.1 Carrier models

Table 1 Adsorption energy, bond length and atomic spacing of H2O molecules on different carrier models

载体	吸附能/(kcal/mol)	吸附后H—O键长/nm	吸附后原子间距/nm
ZSM-5分子筛	-9.743	0.1076	0.3789
γ-Al₂O₃	-11.610	0.1022	0.3026

Fig.2 Active component β-MnO2 models

Table 2 Adsorption energy of different adsorption configurations of H2O molecules on surface of different active components

吸附构型	H₂O分子在β-MnO₂（0 0 1）上的吸附能/(kcal/mol)	H₂O分子在β-MnO₂（+Ce）上的吸附能/(kcal/mol)
H₂O分子中H吸附到β-MnO₂的Mn	-6.577	-3.857
H₂O分子中H吸附到β-MnO₂的O	-7.943	-5.335
H₂O分子中O吸附到β-MnO₂的Mn	-10.982	-7.396
H₂O分子中O吸附到β-MnO₂的O	-6.044	-4.769

Fig.3 Reactant and product models

Table 3 Reaction activation energy of SO2 molecule and different active components

活性组分类型	反应活化能/（kcal/mol）
β-MnO₂（0 0 1）	15.473
β-MnO₂（+Ce）	33.581

Fig.4 Schematic diagram of flue gas denitration experimental device

Fig.5 Denitration efficiency of Mn-Fe-Ce/ZSM-5 and Mn-Fe/γ-Al2O3 catalysts at different temperatures

Fig.6 Denitration efficiency of Mn-Fe-Ce/ZSM-5 catalyst under different Ce loadings

Fig.7 Denitration efficiency of Mn-Fe-Ce/ZSM-5 and Mn-Fe/γ-Al2O3 catalysts with different H2O volume fractions

Fig.8 Denitration efficiency of Mn-Fe-Ce/ZSM-5 and Mn-Fe/γ-Al2O3 catalysts at different SO2 concentrations

Fig.9 SEM images of Mn-Fe-Ce/ZSM-5 and Mn-Fe/γ-Al2O3 catalysts before and after reaction

Fig.10 XRD patterns of Mn-Fe-Ce/ZSM-5 and Mn-Fe/γ-Al2O3 catalysts before and after reaction

Fig.11 TG and DTG curves of Mn-Fe/γ-Al2O3 catalyst before reaction

Fig.12 TG and DTG curves of Mn-Fe/γ-Al2O3 catalyst after reaction

Table 4 Physical properties of Mn-Fe-Ce/ZSM-5 and Mn-Fe/γ-Al2O3 catalysts before and after reaction

催化剂类型	比表面积/ (m²/g)	孔容×10²/ (cm³/g)	平均孔径 /nm
Mn-Fe/γ-Al₂O₃（反应前）	129	20	6.9
Mn-Fe/γ-Al₂O₃（反应后）	115	18.1	5.8
Mn-Fe-Ce/ZSM-5（反应前）	308	10	5
Mn-Fe-Ce/ZSM-5（反应后）	303	9.4	4.7

Fig.13 Variation of pore size and pore volume distribution of Mn-Fe/γ-Al2O3 catalyst

Fig.14 Changes in pore size and pore volume distribution of Mn-Fe-Ce/ZSM-5 catalyst before and after reaction

Fig.15 Changes in outlet SO2 concentration with or without oxygen

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