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为原料制备的球形活性炭为载体，采用浸渍法负载锡铈氧化物制得SnOx-CeOx/沥青基球形活性炭系列催化剂，考察了其在低温下的脱硝性能，并利用N2吸/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了表征。结果表明，向CeOx/PSAC催化剂中添加SnOx后其脱硝活性显著增加；催化剂的脱硝活性随金属担载量的增加呈现先升高后降低的趋势。Sn(w=5%)Ce(w=13%)/PSAC（本文以Sn(5%)Ce(13%)/PSAC表示）催化剂具有最高的脱硝活性，在100～300 oC温度范围内得到最高NO转化率98%。添加SnOx后提高了CeO2在载体表面的分散性，而且Sn4+替代Ce4+掺杂于立方相CeO2晶格中形成固溶体，从而提高了催化剂的脱硝活性。此外，与单组份铈催化剂相比，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 medical treatment, environmental protection and other fields because of its advantages of high specific surface area, high mechanical strength, high packing intensity and low fluid resistance. A series of SnOx-CeOx/PSAC catalysts were prepared by impregnation method using PSAC prepared from high softening point petroleum pitch as support. And their catalytic performance were evaluated by the low-temperature selective catalytic reduction (SCR) of NO with NH3. The obtained samples were mainly 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 in comparison with CeOx/PSAC catalyst, and the trend of NO conversion firstly increases and then decreases with the increasing of metal loading. The Sn(5%)Ce(13%)/PSAC catalyst exhibits the highest NO removal activity, where the highest NO conversion can reach about 98% in the temperature range of 100~300 oC. The reason is mainly attributed to the improved dispersion of cerium oxide on the surface of PSAC by addition of SnOx, and the formation of solid solution between SnOx and CeOx with the fluorite-type structure, which may be caused by the incorporation of Sn4+ into the crystal lattice of CeO2. Furthermore, there are a certain amount of Ce3+, and higher percentage of surface chemisorbed oxygen 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. NO conversion of Sn(5%)Ce(13%)/PSAC catalyst is still about 80% at 260 oC after the introduction of SO2 in the feed gas for 420 min.
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图 2 沥青球形活性炭的N2吸/脱附等温线（a）和孔径分布图（b）
Figure 2. (a) N2 adsorption/desorption isotherms and (b) corresponding pore size distribution curves of PSAC
图 4 不同金属担载量时SnOx-CeOx/PSAC催化剂的脱硝活性
Figure 4. NO removal activities over SnOx-CeOx/PSAC catalysts with different metal loadings
图 5 260 oC下SO2对Sn(5%)Ce(13%)/PSAC和Ce/PSAC催化剂脱硝活性的影响
Figure 5. Effect of SO2 on NO removal activities over Sn(5%)Ce(13%)/PSAC and Ce/PSAC catalysts at 260 oC
图 6 不同金属担载量时SnOx-CeOx/PSAC催化剂的N2吸/脱附曲线（a）和孔径分布图（b）
Figure 6. (a) Nitrogen adsorption/desorption isotherms and (b) corresponding pore size distribution curves of SnOx-CeOx/PSAC catalysts with different metal loadings
图 9 Sn(5%)Ce(13%)/PSAC催化剂的C 1s（a），O 1s（b），Ce 3d（c）和Sn 3d（d）的XPS分峰谱图
Figure 9. XPS spectra of C 1s (a), O 1s(b), Ce 3d (c) and Sn 3d (d) for Sn(5%)Ce(13%)/PSAC
表 1 沥青球形活性炭的孔结构参数
Table 1. Pore structure parameters of PSAC
Sample SBET/(m2·g-1) Smic/(m2·g-1) Vtotal/(cm3·g-1) Vmic/(cm3·g-1) PSAC 1522 1373 0.66 0.60 Note: SBET: BET specific surface area; Smic: Micropore surface area; Vtotal: Total pore volume; Vmic: Micropore volume 
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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
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表 3 Sn(5%)Ce(13%)/PSAC催化剂表面元素浓度
Table 3. Surface atomic concentrations of Sn(5%)Ce(13%)/PSAC catalyst
Surface atomic concentration
(%)Relative atomic fraction/ % Sn C Ce O Oβ Oα 1.08 82.92 1.96 14.04 78.7 21.3
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