Experimental study on selective catalytic reduction of NO by C3H6 over Fe/Ti-PILC catalysts
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摘要: 采用二氧化钛对蒙脱土进行柱撑改性后,以离子交换法制备了铁负载二氧化钛柱撑蒙脱土催化剂Fe/Ti-PILC,考察了其在富氧条件下催化C3H6选择性还原NO(C3H6-SCR)的性能。并借助N2等温吸附-脱附、XRD、UV-vis、H2-TPR、Py-FTIR等表征方法研究了催化剂的结构与性能之间的关系。结果表明,所制备的19Fe/Ti-PILC催化剂在400 ℃时即可实现到NO的完全脱除,N2选择性能够达到90%以上。且具有较好的抗水蒸气和抗SO2的能力。N2吸附-脱附和XRD结果显示,蒙脱土的结构被撑开,交联柱撑有效,形成了较大的比表面积和孔体积。UV-vis结果表明,催化剂的脱硝活性与铁氧低聚物种FexOy的含量有关,Py-FTIR结果表明,催化剂表面同时存在Lewis酸和Brønsted酸,Fe3+负载到柱撑黏土中能够显著增加Lewis酸的含量,Lewis酸是影响催化剂脱硝活性的影响因素之一。H2-TPR表征表明,催化剂在400 ℃左右有较强的还原能力,催化剂的还原能力主要体现为Fe3+→Fe2+的还原。Abstract: Ti-pillared interlayer clay (PILC)-based catalysts ion exchanged with Fe were prepared and used for selective catalytic reduction of NOx using propylene as the reducing agent under oxygen-rich conditions. The relationship between structure and properties of the catalysts was studied using N2-adsorption/desorption, XRD, UV-vis, H2-TPR, and Py-FTIR. The results show that the prepared 19Fe/Ti-PILC catalyst can achieve complete removal of NO at 400 ℃, and N2 selectivity can reach over 90% and has better resistance to water vapor and SO2. N2-isothermal adsorption/desorption and XRD results show that structure of montmorillonite is opened, cross-linked pillars are effective, and a large specific surface area and pore volume are formed. UV-vis results show that the denitrification activity of the catalyst is related to content of oligomeric FexOy. Py-FTIR results show that both Lewis acid and Brønsted acid are presented on the catalyst surface. Fe3+ loading into the pillared clay can significantly increase the Lewis acid content. Lewis acid is one of the influencing factors on the denitrification activity of the catalyst. H2-TPR indicates that the catalyst has a strong reduction ability at about 400 ℃, and the reduction ability of the catalyst is mainly represented by the reduction of Fe3+→Fe2+.
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Key words:
- oxygen-rich conditions /
- pillared clay /
- selective catalytic reduction /
- propylene
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表 1 不同负载量的催化剂的织构特征
Table 1 Properties of catalysts with different loadings of Fe
Catalyst Fe w/(mg·g-1) ABET/(m2·g-1) Pore volume v/(cm3·g-1) Pore diameter d/nm Original clay - 24 0.099 16.44 Ti-PILC - 203 0.240 4.73 13Fe/Ti-PILC 135.2 166 0.207 4.97 19Fe/Ti-PILC 192.1 190 0.222 5.07 22Fe/Ti-PILC 221.0 179 0.209 4.73 表 2 通过UV-vis光谱的定量分析确定的子带面积百分比
Table 2 Percentage of the area of the sub-bands by quantitative analysis of the UV-vis spectra
Catalyst Percentage /% I1 I2 I3 5Fe/Ti-PILC 70 14 16 13Fe/Ti-PILC 56 23 21 19Fe/Ti-PILC 41 29 30 22Fe/Ti-PILC 39 24 37 I1, I2, and I3 represent isolated Fe3+ species, small FexOy oligomers, and Fe2O3 particles species, respectively 表 3 不同负载量的催化剂中Brønsted酸和Lewis酸的含量
Table 3 Brønsted and Lewis acid content of different catalysts
Sample 40 ℃ desorption /(μmol·g-1) 170 ℃ desorption /(μmol·g-1) 300 ℃ desorption /(μmol·g-1) B L B L B L Ti-PILC 9.99 382.61 4.05 127.14 2.78 83.83 5Fe/Ti-PILC 46.84 398.59 31.06 197.24 19.36 133.96 13Fe/Ti-PILC 13.96 636.18 10.34 189.85 5.17 122.80 19Fe/Ti-PILC 7.17 688.40 37.83 311.51 24.94 234.59 -
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