Removal of NO at low temperature and in the absence of ammonia over spherical activated carbon loaded with MnOx-CeO2 and urea
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摘要: 以MnOx-CeO2为活性组分、以尿素为还原剂，制备了球形活性炭（SAC）担载MnOx-CeO2和尿素的复合催化剂，利用扫描式电子显微镜-能谱仪（SEM-EDS）、X射线衍射（XRD）和低温N2吸附-脱附等对催化剂的物理化学结构进行了表征，考察了该催化剂在低温（30-90 ℃）和没有氨气情况下对NO的选择性催化还原（SCR）性能。结果表明，在30-50 ℃的反应温度下，炭载体的微孔孔容仍是NO吸附与氧化的主要活性位点；而在70-90 ℃的反应温度下，锰铈金属氧化物成为NO吸附与氧化的主要活性位点，从而提高了催化剂的SCR反应活性。当反应温度为90 ℃、空速为6000 h-1、NO和O2浓度分别为0.05%和20%时，担载8% Mn（锰铈物质的量比为1:1）和10%尿素的催化剂的MOx稳态脱除率可达85.6%，实现了在低温、无氨状况下的高效脱硝。Abstract: A complex catalyst was prepared by loading MnOx-CeO2 and urea on spherical activated carbon (SAC) for the selective catalytic reduction (SCR) of NO at low temperature (30-90 ℃) in the absence of ammonia. The complex catalyst was characterized by scanning electron microscopy-energy dispersive spectrum (SEM-EDS), X-ray diffraction (XRD), and N2 sorption. The results show that at 30-50 ℃, the micropores of SAC acts as the main active sites for NO adsorption and reaction, whereas at 70-90 ℃, MnOx-CeO2 turns to be the main active sites for NO adsorption and reaction; the urea-SCR activity is enhanced by MnOx-CeO2 in a wide temperature range. Over the complex catalyst loaded with 8% Mn (the mole ratio of Mn to Ce is 1) and 10% urea, the steady conversion of MOx reaches 85.6% in the absence of ammonia, under the conditions of 90 ℃, 0.05% NO, 20% O2 and a space velocity of 6000 h-1.
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Key words:
- spherical activated carbon /
- MnOx-CeO2 /
- urea /
- NO /
- selective catalytic reduction
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图 1 400-8(Mn-Ce)/SAC的SEM照片及金属氧化物在400-8(Mn-Ce)/SAC上的分布
Figure 1 SEM image of 400-8(Mn-Ce)/SAC ((a), (b)), Mn mapping of 400-8(Mn-Ce)/SAC (c) and Ce mapping of 400-8(Mn-Ce)/SAC (d)
图 2 不同煅烧温度下的8(Mn-Ce)/SAC的XRD谱图
Figure 2 XRD patterns of 8(Mn-Ce)/SAC calcined at different temperatures:a: 300 ℃; b: 400 ℃; c: 500 ℃; d: 600 ℃
图 3 尿素担载量不同的复合催化剂的N2吸附-脱附等温线(a)及其DFT孔径分布图(b)
Figure 3 Nitrogen adsorption-desorption isotherms (a) and DFT pore size distributions (b) of the catalysts with different urea loadings
图 4 金属氧化物担载量对urea-SCR反应活性的影响
Figure 4 Effect of metal oxides loading on stationary-state NOx conversion over urea-supported catalysts
(reaction conditions: 0.05% NO, 20% O2, balance N2, temperature=30-90 ℃, space velocity=6000 h-1)
图 5 锰铈物质的量比对urea-SCR反应活性的影响
Figure 5 Effect of Ce/Mn molar ratio on stationary-state NOx conversion over urea-supported catalysts
(reaction conditions: 0.05% NO, 20% O2, balance N2, reaction temperature=30-90 ℃, space velocity=6000 h-1)
图 6 金属氧化物煅烧温度对urea-SCR反应活性的影响
Figure 6 Effect of calcination temperature on stationary-state NOx conversion over urea-supported catalysts
(reaction conditions: 0.05% NO, 20% O2, balance N2, reaction temperature=30-90 ℃, space velocity=6000 h-1)
图 7 尿素担载量对urea-SCR反应活性的影响
Figure 7 Effect of urea loading on stationary-state NOx conversion over urea-supported catalysts
(reaction conditions: 0.05% NO, 20% O2, balance N2, reaction temperature=30-90 ℃, space velocity=6000 h-1)
图 8 NO与O2进气浓度对urea-SCR反应活性的影响
Figure 8 Effect of NO (a) and O2 (b) feed concentration on stationary-state NOx conversion over urea-supported catalysts
(sample: 400-8(Mn-Ce)/SAC-10; reaction conditions: 0.01%-0.1% NO, 2%-20% O2, balance N2, reaction temperature=30-90 ℃, space velocity=6000 h-1)
图 9 空速对urea-SCR反应活性的影响
Figure 9 Effect of the space velocity on the stationary-state NOx conversion over urea-supported catalysts
(sample: 400-8(Mn-Ce)/SAC-10; reaction conditions: 0.05% NO, 20% O2, balance N2, reaction temperature=30-90 ℃, space velocity=3000-12000 h-1)
表 1 复合催化剂的孔结构参数
Table 1 Pore structural parameters of the catalysts with different urea loadings
Sample ABETa/(m2·g-1) Amicb/(m2·g-1) vtc/(cm3·g-1) vmicd/(cm3·g-1) d pe /nm SAC 1411 1295 0.62 0.52 0.73 400-8(Mn-Ce)/SAC 710 648 0.32 0.26 0.66 400-8(Mn-Ce)/SAC-5 673 614 0.34 0.25 0.85 400-8(Mn-Ce)/SAC-10 578 528 0.26 0.22 0.67 400-8(Mn-Ce)/SAC-15 476 428 0.22 0.17 0.93 400-8(Mn-Ce)/SAC-20 380 322 0.19 0.13 0.79 a: BET surface area, b: micropore surface area (< 2 nm), c: total pore volume (p/p0=0.996), d: micropore volume (< 2 nm), e: average pore diameter 
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