Denitration Performance of SnOx-CeOx/Pitch-Based Spherical Activated Carbon Catalysts for Selective Catalytic Reduction of NO
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摘要: 以高软化点石油沥青原料制备的沥青基球形活性炭(PSAC)为载体,采用浸渍法负载锡、铈氧化物制备SnOx-CeOx/PSAC系列催化剂,考察催化剂在低温下的脱硝性能,并采用N2吸附/脱附、X射线衍射(XRD)、X射线光电子能谱(XPS)等方法对催化剂进行表征。结果表明,在CeOx/PSAC催化剂中添加SnOx后催化剂的脱硝活性显著增加,但随着金属担载量(质量分数)增加,脱硝活性呈现先升高后降低的趋势,Sn、Ce担载量分别为5%和13%的SnOx-CeOx/PSAC(以Sn(5%)Ce(13%)/PSAC表示)催化剂具有最高的脱硝活性,在该催化剂条件下,100~300 ℃时可得到最高的NO转化率(98%)。添加SnOx后,CeO2在载体表面的分散性得到提高,由于Sn4+替代Ce4+掺杂于立方相CeO2晶格中形成固溶体,因而催化剂的脱硝活性提高。此外,与单组分铈催化剂相比,Sn(5%)Ce(13%)/PSAC催化剂具有较好的抗SO2毒化性能。Abstract: Pitch-based spherical activated carbon (PSAC) is widely used in biomedicine, environmental protection and other practical fields because of its advantages of high specific surface area, high mechanical strength, high packing intensity and low fluid resistance. In this study, series of SnOx-CeOx/PSAC catalysts were prepared by the impregnation method using PSAC prepared from high softening point petroleum pitch as the support. Their catalytic performances were evaluated in the low-temperature selective catalytic reduction (SCR) of NO with NH3. The catalysts obtained were characterized by nitrogen adsorption/desorption, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that SnOx-CeOx/PSAC catalyst exhibits higher SCR activity than CeOx/PSAC catalyst, and the NO conversion rate first increases and then decreases with the increase of metal loading. The Sn(5%)Ce(13%)/PSAC catalyst exhibits the highest NO removal activity, and the highest NO conversion rate reaches 98% in the temperature range of 100~300 ℃. This is mainly due to the improved dispersion of cerium oxide on the surface of PSAC in the presence of SnOx, and the formation of a solid solution between SnOx and CeOx with a fluorite-type structure probably caused by the incorporation of Sn4+ into the crystal lattice of CeO2. Furthermore, a certain amount of Ce3+ and a high percentage of chemisorbed oxygen exist on the catalyst surface because of the synergistic effect between tin and cerium oxides. These factors result in the excellent NH3-SCR performance of the Sn(5%)Ce(13%)/PSAC catalyst. Compared with CeOx/PSAC catalyst, SnOx-CeOx/PSAC catalyst exhibits a higher resistance to SO2 poisoning. The NO conversion rate of the Sn(5%)Ce(13%)/PSAC catalyst retains at 80% at 260 ℃ after the introduction of SO2 in the feed gas for 420 min.
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表 1 PSAC的孔结构参数
Table 1. Pore structure parameters of PSAC
SBET/(m2·g−1) Smic/(m2·g−1) Vtotal/(cm3·g−1) Vmic/(cm3·g−1) 1522 1373 0.66 0.60 SBET—BET specific surface area; Smic—Micropore surface area; Vtotal—Total pore volume; Vmic—Micropore volume 表 2 不同催化剂的BET比表面积和孔结构
Table 2. BET specific surface area and pore structure of various catalysts
Sample SBET/
(m2·g−1)Smic/
(m2·g−1)Vtotal/
(cm3·g−1)Vmic/
(cm3·g−1)Sn(1%)Ce(3%)/PSAC 926 861 0.36 0.35 Sn(3%)Ce(8%)/PSAC 754 668 0.35 0.28 Sn(5%)Ce(13%)/PSAC 684 624 0.31 0.26 Sn(7%)Ce(18%)/PSAC 513 452 0.24 0.19 表 3 Sn(5%)Ce(13%)/PSAC催化剂的表面原子摩尔分数
Table 3. Surface atomic mole fraction of Sn(5%)Ce(13%)/PSAC catalyst
Mole fraction/% Relative atomic ratio/%1) Sn C Ce O Oβ Oα 1.08 82.92 1.96 14.04 78.7 21.3 1) Calculated by the peak area -
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