Preparation and NH3-SCR catalytic performance of CeTiOx catalysts with different pore structures
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摘要: 为探究催化剂的孔结构对催化剂脱硝活性的影响，采用溶胶凝胶法分别制备了三维有序大孔-介孔(3DOM-m) CeTiOx、三维有序大孔(3DOM) CeTiOx、三维有序介孔(3DOm) CeTiOx及无序孔(DM) CeTiOx等四种不同孔结构的催化剂。NH3-SCR测试结果表明，催化剂活性依次为3DOM-m CeTiOx>3DOm CeTiOx>3DOM CeTiOx>DM CeTiOx，3DOM-m CeTiOx表现出更优异的催化活性，NO转化率在60000 h−1、250–400 ℃时超过90%。通过XRD、SEM、BET、NH3-TPD、in-situ DRIFTS等技术对催化剂进行表征分析。结果表明，催化剂的比表面积并不是决定CeTiOx脱硝活性的主导因素。3DOM-m CeTiOx具有高度有序的大孔-介孔结构、丰富的Brønsted酸酸性位点，进而提高了催化剂的脱硝活性。3DOM-m CeTiOx催化剂在NH3-SCR反应过程中同时遵循E-R机理和L-H机理。Abstract: To investigate the influence of pore structure on the catalytic activity of catalysts, four catalysts including three-dimensionally ordered macroporous-mesoporous (3DOM-m) CeTiOx, three-dimensionally ordered macroporous (3DOM) CeTiOx, three-dimensionally ordered mesoporous (3DOm) CeTiOx and disordered mesoporous (DM) CeTiOx were synthesized by the sol-gel method. The NH3-SCR denitration testing results show that the performance of the catalysts with different pore structures follows the sequence of 3DOM-m CeTiOx>3DOm CeTiOx>3DOM CeTiOx>DM CeTiOx, and the 3DOM-m CeTiOx shows an excellent catalytic activity, with more than 90% NO conversion in the range of 250–400 ℃ at a GHSV of 60000 h−1 . The characterization of catalysts by XRD, SEM, BET, NH3-TPD and in-situ DRIFTS indicates that the surface area is not the dominant factor determining the catalytic activity of CeTiOx. 3DOM-m CeTiOx has a highly ordered macroporous-mesoporous structure and abundant Bronsted acidic sites, thereby improving the denitrification activity. The NH3-SCR reaction over the 3DOM-m CeTiOx mainly follows the L-H and E-R mechanisms.
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Key words:
- CeTiOx /
- 3DOM structure /
- ordered mesoporous structure /
- NH3-SCR
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图 1 不同孔结构的CeTiOx催化剂NO转化率
Figure 1 NO conversions over CeTiOx catalysts with different pore structures
图 2 不同孔结构CeTiOx催化剂的XRD谱图（a）及小角XRD谱图（b）
Figure 2 XRD patterns (a) and small angle XRD patterns (b) of CeTiOx catalysts with different pore structures
图 3 PMMA模板及CeTiOx催化剂的SEM照片
Figure 3 SEM images of PMMA microspheres and CeTiOx catalysts
(a): PMMA microspheres; (b), (c): 3DOM-m CeTiOx; (d): 3DOM CeTiOx; (e): 3DOm CeTiOx; (f): DM CeTiOx.
图 4 不同孔结构 CeTiOx催化剂的氮气吸附-脱附等温线（a）及介孔分布（b）
Figure 4 N2 adsorption-desorption isotherm (a) and mesoporous distribution (b) of CeTiOx catalysts with different pore structures
图 5 不同孔结构CeTiOx催化剂的NH3-TPD谱图
Figure 5 NH3-TPD profiles of CeTiOx catalysts with different pore structures
图 6 CeTiOx催化剂表面 NH3吸附in-situ DRIFTS 谱图
Figure 6 In situ DRIFTS of NH3 with CeTiOx catalysts at different temperatures
(a): 3DOM-m CeTiOx; (b): 3DOM CeTiOx; (c): 3DOm CeTiOx; (d): DM CeTiOx.
图 7 不同孔结构CeTiOx催化剂B酸、L酸量计算结果(50 ℃)
Figure 7 Acid content (a) and amount (b) of CeTiOx catalysts with different pore structures at 50 ℃
图 8 CeTiOx催化剂表面 NO+O2吸附 in-situ DRIFTS 谱图
Figure 8 In situ DRIFTS of NO+O2 on CeTiOx catalysts at different temperatures
(a): 3DOM-m CeTiOx; (b): 3DOM CeTiOx; (c): 3DOm CeTiOx; (d): DM CeTiOx.
图 9 3DOM-m CeTiOx催化剂表面NH3吸附饱和后通NO+O2 (a), NO+O2吸附饱和后通NH3 (b) in-situ DRIFTS谱图(200 ℃)
Figure 9 In-situ DRIFTS of NO+O2 reacting with pre-adsorbed NH3 (a), NH3 reacting with pre-adsorbed NO+O2 (b) over the 3DOM-m CeTiOx catalyst at 200 ℃
表 1 不同孔结构CeTiOx催化剂的结构
Table 1 Textural properties of CeTiOx catalysts with different pore structures
Catalyst Surface area
A/(m2·g−1)Pore volume v/(cm3·g−1) Average pore size d/nm 3DOM-m CeTiOx 107.3 0.217 8.1 3DOM CeTiOx 60.9 0.119 7.4 3DOm CeTiOx 257.6 0.348 5.4 DM CeTiOx 49.3 0.097 7.5 
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表 2 不同孔结构CeTiOx催化剂的NH3-TPD计算
Table 2 The results of NH3-TPD
Catalyst Weak acid amount/(μmol∙g−1) Medium strong acid amount/(μmol∙g−1) Total acid amount/(μmol∙g−1) 3DOM-m CeTiOx 101 35 136 3DOM CeTiOx 60 12 72 3DOm CeTiOx 71 26 97 DM CeTiOx 56 8 63
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