Influence of different supports on the physicochemical properties and denitration performance of the supported MnCe-based catalysts for NH3-SCR
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摘要: 选取TiO2、SAPO-34、Al2O3三种常用载体，通过浸渍法以Mn-Ce-O为活性组分制备了负载型MnCeOx脱硝催化剂。采用XRD、BET、H2-TPR、XPS、Py-FTIR等手段对催化剂的固相结构、比表面积、还原性能、表面元素及酸量进行表征分析。结果表明，MnCeOx/SAPO-34催化剂具有最大的比表面积（439.87 m2/g），酸量适中，还原性能最差；MnCeOx/Al2O3催化剂中Mn4+、Ce3+所占比例较高，但酸性最弱；MnCeOx/TiO2催化剂还原性能最优，表面Mn、Ce元素浓度最高，并具有大量Lewis酸性位。通过气固相催化反应装置对催化剂性能进行了NH3-SCR脱硝评价，结果表明，MnCeOx/TiO2催化剂具有较好的脱硝性能，反应温度为280 ℃时，NO转化率达100%（空速为42000 h-1）；与催化剂物化性质对比分析，催化剂的氧化还原能力和Lewis酸性位对其脱硝性能至关重要。Abstract: A series of supported Mn-Ce-based catalysts were prepared using TiO2, SAPO-34, and Al2O3 as supports. The physicochemical properties of the obtained catalysts, such as structure, specific surface area, reduction properties, surface elements and acidity were characterized with XRD, BET, H2-TPR, XPS and Py-FTIR. The results showed that MnCeOx/SAPO-34 catalyst exhibited a larger specific surface area (439.87 m2/g), medium amount of Lewis acid sites and the weakest reduction property. In the MnCeOx/Al2O3 catalyst, the concentration of Mn4+ and Ce3+ was relatively high, and the amount of acid sites is the lowest. However, TiO2 as the catalyst support could enhance the reduction property, and increase the amount of Lewis acid sites and the concentration of Mn and Ce. NH3-SCR performances of the catalysts were evaluated using a flow type fixed bed reactor. The results showed that MnCeOx/TiO2 catalyst presented the best catalytic performance, over which near 100% NO conversion was reached at 280 ℃ under a gas hourly space velocity of 42000 h-1. The combination of characterization and reaction results indicated that the good reduction behavior and large amount of Lewis acid sites were beneficial to the enhancement of the catalytic performance for low-temperature NH3-SCR reaction.
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Key words:
- supports /
- Mn-Ce oxides /
- reducibility /
- surface acidity /
- low-temperature NH3-SCR
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图 3 催化剂的N2吸附-脱附等温线和孔径分布
Figure 3 N2 adsorption-desorption isotherms and pore size distribution curves of the catalysts
图 5 催化剂Mn 2p、Ce 3d和O 1s轨道XPS谱图
Figure 5 Mn 2p(a), Ce 3d(b) and O 1s(c) XPS spectra of the catalysts
表 1 催化剂的结构特征
Table 1 Structural parameters of the catalysts
Sample Specific surface area A/ (m2·g-1) Mean pore diameter d/nm Total pore volume v/(cm3·g-1) TiO2 108.72 20.68 0.59 MnCeOx/TiO2 101.21 21.39 0.54 SAPO-34 479.32 1.59 0.49 MnCeOx/SAPO-34 439.87 2.13 0.23 Al2O3 230.15 14.56 0.93 MnCeOx/Al2O3 223.57 15.21 0.85 
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表 2 催化剂表面原子浓度及比例
Table 2 Atomic concentration and ratio of the catalysts
Catalyst Atomic concentration w/% Atomic ratio /% Mn Ce Mn2+/Mnn+ Mn3+/Mnn+ Mn4+/Mnn+ Ce3+/Cen+ MnCeOx/TiO2 1.96 2.32 10.91 50.97 38.11 18.69 MnCeOx/SAPO-34 1.02 1.11 32.23 36.51 31.25 15.12 MnCeOx/Al2O3 0.53 0.78 16.41 35.07 48.51 20.97
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表 3 催化剂表面B酸和L酸分布及浓度
Table 3 Concentration of pyridine on Brønsted (B) and Lewis acid (L) sites
Sample 100 ℃ /(mmol·g-1) 200 ℃ /(mmol·g-1) 300 ℃ /(mmol·g-1) B L B L B L MnCeOx/TiO2 0.009 0.184 0.006 0.134 0.002 0.087 MnCeOx/SAPO-34 0.018 0.069 0.009 0.025 0.003 0.005 MnCeOx/Al2O3 0 0.058 0 0.039 0 0.013
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