低温选择性催化还原脱硝Mn-Ce/TiO<sub>2</sub>催化剂的Pb中毒与再生研究

闫东杰; 郭通; 玉亚; 陈兆辉

doi:10.1016/S1872-5813(21)60003-8

低温选择性催化还原脱硝Mn-Ce/TiO₂催化剂的Pb中毒与再生研究

doi: 10.1016/S1872-5813(21)60003-8

西安建筑科技大学环境与市政工程学院，陕西省环境工程重点实验室，陕西西安 710055

基金项目: 陕西省重点研发计划项目（2020SF-432）和陕西省现代建筑研究院科研项目（XDKY-2020-04）资助

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E-mail: yandongjie_2000@163.com

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出版历程
- 收稿日期: 2020-09-11
- 修回日期: 2020-10-11
- 刊出日期: 2021-01-29

Lead poisoning and regeneration of Mn-Ce/TiO₂ catalysts for NH₃-SCR of NO_x at low temperature

Shaanxi Key Laboratory of Environmental Engineering, College of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China

Funds: The project was supported by the Key R & D project of Shaanxi Province (2020SF-432) and the research project of Shaanxi Modern Architecture Design & Research Institute (XDKY-2020-04)

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Corresponding author: E-mail: yandongjie_2000@163.com

摘要

摘要: 考察了Pb对Mn-Ce/TiO₂低温选择性催化还原（SCR）脱硝活性的影响，并对Pb中毒的催化剂进行了再生；结合氮吸附、SEM、XRD、FT-IR、H₂-TPR和NH₃-TPD等表征结果，研究了Mn-Ce/TiO₂催化剂Pb中毒和再生活性恢复的原因。结果表明，Pb对Mn-Ce/TiO₂催化剂脱硝活性有明显的抑制作用；当Pb的含量为11%时，Mn-Ce/TiO₂催化剂在180 ℃下的脱硝效率从原来100%下降至44%。Pb在Mn-Ce/TiO₂中的掺杂使得催化剂的比表面积以及活性组分Mn⁴⁺和Ce³⁺的含量降低，影响了氧化还原循环反应（Mn⁴⁺ + Ce³⁺ ↔ Mn³⁺ + Ce⁴⁺）的进行；此外，Pb的加入破坏了催化剂的酸性位点，阻碍了催化剂对NH₃的吸附和活化。经硝酸再生后的Mn-Ce/TiO₂催化剂的脱硝活性几乎完全恢复，在80–150 ℃下其脱硝活性甚至超过新鲜未中毒的催化剂，其原因主要在于硝酸再生能恢复催化剂的氧化还原能力、增大比表面积、并形成新的酸位点。
- 低温选择性催化还原脱硝 /
- Mn-Ce/TiO₂ /
- Pb中毒 /
- 再生
Abstract: The effect of lead on the catalytic performance of Mn-Ce/TiO₂ catalysts in the selective catalytic reduction (SCR) of NO_x with ammonia at low temperature was investigated; with the help of nitrogen sorption, XRD, FT-IR spectroscopy, H₂-TPR and NH₃-TPD characterization, the causes of lead poisoning and acid regeneration were clarified. The results indicate that the doping of Pb in Mn-Ce/TiO₂ leads to a significant decrease of the low-temperature SCR activity; with a Pb loading of 11%, the conversion of NO over Mn-Ce/TiO₂ at 180 °C decreases from original 100% on the fresh catalyst to 44% on the Pd-poisoned catalyst. The presence of Pb may reduce the content of active Mn⁴⁺ and Ce³⁺ species on the Mn-Ce/TiO₂ catalyst, which suppresses the redox cycle of Mn⁴⁺ + Ce³⁺ ↔ Mn³⁺ + Ce⁴⁺; moreover, the decrease of surface acidity on the Mn-Ce/TiO₂ catalyst by the doping of Pb is also disadvantageous to the adsorption and activation of NH₃. The Pd-poisoned Mn-Ce/TiO₂ can be regenerated by nitric acid treatment; after the regeneration, the catalytic activity of Mn-Ce/TiO₂ in NH₃-SCR of NO is almost completely recovered and even exceeds that of the fresh catalyst at 80–150 °C. The nitric acid treatment can restore the redox capacity of Mn-Ce/TiO₂, increase the surface area, and create new acid sites, which contribute to recovery of the activity of Pb-poisoned Mn-Ce/TiO₂ catalyst in NH₃-SCR.
- selective catalytic reduction /
- Mn-Ce/TiO₂ /
- Pb poisoning /
- regeneration

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图 1 测试装置示意图

1: gas cylinders; 2: pressure reducing valve; 3: mass-flow meters; 4: mixed gas cylinder; 5: catalytic reactor; 6: tube furnace; 7: flue gas analyzer; 8: absorption pot for tail gas

Figure 1 Schematic diagram of the catalytic test device for the selective catalytic reduction (SCR) of NO_x with ammonia at low temperature

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图 2 Pb(x)-Mn-Ce/TiO₂系列催化剂的脱硝活性

Figure 2 Activity of the Pb( x )-Mn-Ce/TiO₂ catalysts with different Pd loadings ( x ) in NH₃-SCR of NO reaction conditions: NO =6×10⁻⁴, NH₃ = 6.6×10⁻⁴, O₂ = 3%−5%, GHSV = 8000 h⁻¹

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图 3 不同再生方法的Pb(11%)-Mn-Ce/TiO₂催化剂脱硝活性

Figure 3 Activity of the Pb(11%)-Mn-Ce/TiO₂ catalyst regenerated by different methods

reaction conditions: φ_NO = 6×10⁻⁴, $ {\varphi _{{{\rm{NH}}_3}}} $ = 6.6×10⁻⁴, $ {\varphi _{{{\rm{O}}_2}}} $ = 3%−5%, GHSV = 8000 h⁻¹

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图 4 不同硝酸浓度再生的Pb(11%)-Mn-Ce/TiO₂催化剂脱硝活性

Figure 4 Activity of the Pb(11%)-Mn-Ce/TiO₂ catalyst regenerated by washing with nitric acid of different concentrations

reaction conditions: φ_NO = 6×10⁻⁴, $ {\varphi _{{{\rm{NH}}_3}}} $ = 6.6×10⁻⁴, $ {\varphi _{{{\rm{O}}_2}}} $ = 3%−5%, GHSV = 8000 h⁻¹

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图 5 Pb中毒再生次数对催化剂脱硝活性的影响

Figure 5 Effect of the regeneration times on the activity of the Pb-poisoned Pb(11%)-Mn-Ce/TiO₂ catalyst in the NH₃-SCR of NO_x

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图 6 催化剂SEM照片

Figure 6 SEM images of various catalysts

(a): non-poisoned Mn-Ce/TiO₂(b): non-poisoned Pd(11%)-Me-Ce/TiO₂(c): HNO₃ regeneration

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图 7 催化剂XRD谱图

Figure 7 XRD patterns of the fresh, Pb-poisoned and regenerated Mn-Ce/TiO₂ catalysts

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图 8 催化剂FT-IR谱图

Figure 8 FT-TR spectra of the fresh, Pb-poisoned and regenerated Mn-Ce/TiO₂ catalysts

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图 9 催化剂H₂-TPR谱图

Figure 9 H₂-TPR profiles of the fresh, Pb-poisoned and regenerated Mn-Ce/TiO₂ catalysts

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图 10 催化剂NH₃-TPD谱图

Figure 10 NH₃-TPD profiles of the fresh, Pb-poisoned and regenerated Mn-Ce/TiO₂ catalysts

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表 1 Pb中毒催化剂再生前后的物化特性

Table 1 Textural properties the Mn-Ce/TiO₂ catalysts before and after Pb poisoning and regeneration

Sample	Specific surface area /(m²·g⁻¹)	Total pore volume /(cm³·g⁻¹)	Average pore size /nm
Mn-Ce/TiO₂	77.68	1.58	81.40
Pb(3%)-Mn-Ce/TiO₂	46.32	0.60	51.67
Pb(7%)-Mn-Ce/TiO₂	45.65	0.48	42.28
Pb(11%)-Mn-Ce/TiO₂	35.11	0.18	27.68
$ {\rm{R}}{{\rm{e}}_{{{\rm{H}}_{\rm{2}}}{\rm{O}}}} $	40.86	0.66	64.8
$ {\rm{R}}{{\rm{e}}_{{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}}} $	40.92	0.68	66.23
$ {\rm{R}}{{\rm{e}}_{{\rm{HN}}{{\rm{O}}_{\rm{3}}}}} $	50.94	1.11	86.95

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