Mn/TiO<sub>2</sub>低温SCR催化剂钾中毒机理研究

方鼎立; 张成; 李君臣; 谭鹏; 马仑; 方庆艳; 陈刚

doi:10.19906/j.cnki.JFCT.2023054

Mn/TiO₂低温SCR催化剂钾中毒机理研究

doi: 10.19906/j.cnki.JFCT.2023054

华中科技大学煤燃烧国家重点实验室, 湖北武汉 430074

基金项目: 国家自然科学基金(52076090)、湖北省自然科学基金重点项目（ 2023AFA039）资助

详细信息

通讯作者:
Tel: 158-0273-6522 , E-mail: chengzhang@mail.hust.edu.cn

中图分类号: O643.36
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出版历程
- 收稿日期: 2023-06-01
- 修回日期: 2023-07-03
- 录用日期: 2023-07-03
- 网络出版日期: 2023-09-01
- 刊出日期: 2024-02-02

Study on the mechanism of K-poisoning in Mn/TiO₂ low temperature SCR catalysts

State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Funds: The project was supported by National Natural Science Foundation of China (52076090) and Natural Science Foundation of Hubei Province (2023AFA039) .

摘要

摘要: Mn/TiO₂具有良好的低温NH₃选择性催化还原NO_x（SCR）的活性。烟气中存在的碱金属会从物理和化学上毒害催化剂导致Mn/TiO₂催化剂中毒失活。论文以暴露{101}面TiO₂为载体制备Mn/TiO₂催化剂，采用浸渍法制备K中毒催化剂，研究了Mn/TiO₂低温SCR催化剂钾中毒机理。实验发现，Mn/TiO₂催化剂脱硝效率随K中毒浓度增加而减少；新鲜Mn/TiO₂催化剂表面NH₃-SCR反应由E-R和L-H机理共同控制；K吸附会导致催化剂比表面积降低，催化剂表面Mn⁴⁺、化学吸附氧比例降低，表面酸性位点数量减少，导致脱硝活性降低；同时K更易吸附在Mn顶位以及桥接O位附近，导致NO的吸附活化受到严重遏制，同时削弱NH₃的吸附，使得L-H机理受到阻断，只能以E-R机理控制为主。
- 低温SCR /
- Mn/TiO₂ /
- 钾中毒 /
- 催化剂
Abstract: Mn/TiO₂ has good low temperature NH₃ selective catalytic reduction (SCR) activity for NO_x. The presence of alkali metals in the flue gas can physically and chemically poison the catalyst leading to toxic deactivation of the Mn/TiO₂ catalyst. This study investigated the mechanism of K-poisoning in Mn/TiO₂ low temperature SCR catalysts by preparing K-poisoning Mn/TiO₂ catalysts using exposed {101} surface TiO₂ as a carrier. It was found that the denitrification efficiency of the Mn/TiO₂ catalyst decreased with increasing K-poisoning concentration. Experimental characterisation and DFT calculations showed that the NH₃-SCR reaction on the surface of the fresh Mn/TiO₂ catalyst was controlled by both E-R and L-H mechanisms. K adsorption led to a reduction in the catalyst specific surface area, a decrease in the ratio of Mn⁴⁺ and chemisorbed oxygen on the catalyst surface and a decrease in the number of acidic sites on the surface, resulting in a decrease in denitrification activity; at the same time, K was more likely to adsorb near the Mn top site as well as the bridging O site, resulting in the activation of NO adsorption was severely curtailed and the adsorption of NH₃ was weakened, making the L-H mechanism blocked and the E-R mechanism the main control.
- low-temperature SCR /
- Mn/TiO₂ /
- K-poisoning /
- catalyst

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FIG. 2928. FIG. 2928.

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图 1 催化剂活性评价装置示意图

Figure 1 Schematic diagram of the catalyst activity evaluation device

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图 2 NO转化率随温度的变化

Figure 2 NO conversion versus temperature

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图 3 锐钛矿{101}晶面的（a）SEM和（b）TEM照片

Figure 3 (a) SEM and (b) TEM images of anatase {101} crystal faces

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图 4 Mn/TiO₂催化剂的SEM和EDS照片

Figure 4 SEM and EDS images of Mn/TiO₂ catalyst samples (Ti: cyan; O: red; Mn: purple; K: green)

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图 5 载体和催化剂的XRD谱图

Figure 5 XRD patterns of carrier and catalyst samples

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图 6 Mn/TiO₂催化剂的Mn 2p和O 1s XPS谱图

Figure 6 Mn 2p and O 1s XPS results for Mn/TiO₂ catalysts

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图 7 200 ℃下催化剂表面NO和预先吸附NH₃的反应光谱谱图

Figure 7 Reaction spectra of NO and pre-adsorbed NH₃ on the surface of the catalysts at 200 ℃

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图 8 200 ℃下催化剂表面NH₃和预先吸附NO的反应光谱谱图

Figure 8 Reaction spectra of NH₃ and pre-adsorbed NO on the catalyst surface at 200 ℃

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图 9 Mn/TiO₂及其K中毒催化剂优化构型

Figure 9 Optimised configuration of Mn/TiO₂ and its K-poisoning catalyst

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图 10 NH₃、NO在Mn/TiO₂表面吸附构型

Figure 10 Adsorption configuration of NH₃ and NO on Mn/TiO₂ surface

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图 11 K中毒对Mn/TiO₂影响机理

Figure 11 Mechanism of the effect of K poisoning on Mn/TiO₂

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表 1 催化剂表面元素分析（EDS）

Table 1 Analysis of elemental concentrations on the surface of catalyst samples (EDS)

Sample	K/%	Mn/%	O/%	Ti/%
Mn/TiO₂	−	12.03	51.25	36.72
0.01K- Mn/TiO₂	0.25	11.81	55.37	32.57
0.02K- Mn/TiO₂	0.41	10.77	56.95	31.87
0.045K- Mn/TiO₂	1.23	9.95	56.72	32.10
0.09K- Mn/TiO₂	2.28	9.82	57.12	30.78

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表 2 催化剂的BET参数

Table 2 BET parameters for catalyst samples

Catalyst	BET surface area / (m²·g⁻¹)	Pore volume ×10⁻²/(cm³·g⁻¹)	Average pore diameter/ nm
Mn/TiO₂	52.7	12.1	9.2
0.01K- Mn/TiO₂	44.1	13.0	11.8
0.02K- Mn/TiO₂	44.4	12.9	11.7
0.045K- Mn/TiO₂	45.0	11.6	9.1
0.09K- Mn/TiO₂	42.3	11.3	9.1

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表 3 催化剂表面元素分析（XPS）

Table 3 Analysis of elemental concentrations on the surface of catalyst samples (XPS)

Sample	K/%	Mn/%		O/%
Sample	K/%	Mn²⁺	Mn³⁺+Mn⁴⁺	O_β	O_α
Mn/TiO₂	−	32.6	67.4	49.2	50.8
0.01K- Mn/TiO₂	0.55	35.1	64.9	65.1	34.9
0.02K- Mn/TiO₂	0.53	38.7	61.3	65.2	34.8
0.045K- Mn/TiO₂	2.13	41.7	58.3	72.4	27.6
0.09K- Mn/TiO₂	2.58	47.8	52.2	72.8	27.2

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