球形活性炭担载MnOx-CeO2和三聚氰胺的低温脱硝行为研究

doi:10.15541/jim20160109

摘要/Abstract

摘要：

以MnO_x-CeO₂为活性组分, 以三聚氰胺为还原剂, 制备了球形活性炭(SAC)担载MnO_x-CeO₂和三聚氰胺的复合催化剂, 并考察了该催化剂在低温下(120~180℃)对NO的选择性催化还原(SCR)反应行为。实验还利用扫描电子显微镜-能谱仪(SEM-EDS)、X射线衍射(XRD)和低温N₂吸附法等技术对催化剂进行了表征。结果表明, 当反应温度为180℃、空速为6000 h^-1、NO和O₂浓度分别为0.1%和8%时, 担载8% Mn(摩尔比Mn:Ce固定为1:1)和10%三聚氰胺的催化剂可在8.8 h内实现99%的NO_x转化率。煅烧温度高于400℃将促使MnO_x-CeO₂形成更大的晶体颗粒和更加规整的晶型结构, 从而降低其melamine-SCR活性。三聚氰胺担载量高于15%将造成催化剂比表面积和孔容的急剧减小, 最终导致其稳态NO_x转化率的下降。而金属氧化物担载量的增加和反应温度的升高都有利于Melamine-SCR反应, 且在较宽的NO和O₂浓度范围内, 催化剂的稳态NO_x转化率都能维持在99%左右。

关键词: 球形活性炭, MnOx-CeO₂, 三聚氰胺, NO, 选择性催化还原

Abstract:

A spherical activated carbon (SAC) loaded with MnO_x-CeO₂ and melamine was prepared as the catalyst for selective catalytic reduction (SCR) of NO at low temperature (120-180℃). Physical and chemical properties of the catalysts were characterized by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), and N₂ adsorption-desorption technologies, respectively. The results show that about 99% NO_x conversion for 8.8 h at 180℃ is achieved over the catalyst with 10% melamine and 8% Mn loading (the mole ratio of Mn:Ce was fixed at 1:1) under the condition of 0.1% NO, 8% O₂ and a space velocity of 6000 h^-1. When the calcination temperature is higher than 400℃, the melamine-SCR activity is decreased obviously due to the crystallinity of the metal oxides increasing. When melamine loading is more than 15%, the specific surface area and pore volume of the catalysts decrease significantly, leading to a decline in the stationary-state NO_x conversion. However, the increase of metal oxides loading and reaction temperature is found to be beneficial to melamine-SCR reactivity, and the stationary-state NO_x conversion is always maintained at about 99% over a wide concentration range of NO and O₂.

Key words: spherical activated carbon, MnOx-CeO₂, melamine, NO, selective catalytic reduction

中图分类号:

TQ174

李军, 潘磊, 王际童, 龙东辉, 乔文明, 凌立成. 球形活性炭担载MnO_x-CeO₂和三聚氰胺的低温脱硝行为研究[J]. 无机材料学报, 2016, 31(11): 1205-1211.

LI Jun, PAN Lei, WANG Ji-Tong, LONG Dong-Hui, QIAO Wen-Ming, LING Li-Cheng. Low-temperature Removal of NO by Spherical Activated Carbon Loaded with MnO_x-CeO₂ and Melamine[J]. Journal of Inorganic Materials, 2016, 31(11): 1205-1211.

图/表 12

图1 400-8(Mn-Ce)/SAC的SEM照片(a,b)及Mn、Ce(c,d)金属氧化物在400-8(Mn-Ce)/SAC上的分布

Fig. 1 SEM images of (a, b) 400-8(Mn-Ce)/SAC, (c) Mn and (d) Ce mapping on 400-8(Mn-Ce)/SAC

图2 不同温度煅烧的8(Mn-Ce)/SAC的XRD图谱

Fig. 2 XRD patterns of 8(Mn-Ce)/SAC calcinated at different temperatures(a) 300℃; (b) 400℃; (c) 500℃; (d) 600℃

图3 SAC及不同三聚氰胺担载量的400-8(Mn-Ce)/SAC的N2吸附-脱附等温线

Fig. 3 Nitrogen adsorption-desorption isotherms of SAC and 400-8(Mn-Ce)/SAC with different melamine loadings

表1 SAC及三聚氰胺担载量不同的400-8(Mn-Ce)/SAC的孔结构参数

Table 1 Porosity parameters of SAC and 400-8(Mn-Ce)/SAC with different melamine loadings

Sample	S_BET/(m²·g^-1)	S_mic/(m²·g^-1)	V_t/(cm³·g^-1)	V_mic/(cm³·g^-1)
SAC	1411	1295	0.62	0.52
400-8(Mn-Ce)/SAC	710	648	0.32	0.26
400-8(Mn-Ce)/SAC-5	661	603	0.29	0.25
400-8(Mn-Ce)/SAC-10	578	528	0.26	0.22
400-8(Mn-Ce)/SAC-15	476	428	0.22	0.17
400-8(Mn-Ce)/SAC-20	392	355	0.18	0.14

图 4 400-8(Mn-Ce)/SAC-10的melamine-SCR反应曲线

Fig. 4 Reactivity of NO with melamine on 400-8(Mn-Ce)/ SAC-10Reaction conditions: 0.1% NO, 8% O2, balance N2, reaction temperature = 180℃, space velocity = 6000 h-1

图 5 煅烧温度对melamine-SCR反应的影响

Fig. 5 Effect of calcination temperature on NOx conversion over melamine-supported catalystsReaction conditions: 0.1% NO, 8% O2, balance N2, reaction temperature = 180℃, space velocity= 6000 h-1

图 6 金属氧化物担载量对melamine-SCR反应的影响

Fig. 6 Effect of metal oxides loading on NOx conversion over melamine-supported catalystsReaction conditions: 0.1% NO, 8% O2, balance N2, reaction temperature = 180℃, space velocity = 6000 h-1

图 7 三聚氰胺担载量对melamine-SCR反应的影响

Fig. 7 Effect of melamine loading on NOx conversion over melamine-supported 400-8(Mn-Ce)/SACReaction conditions: 0.1% NO, 8% O2, balance N2, reaction temperature = 180℃, space velocity = 6000 h-1

表2 反应掉的NO与所担载的三聚氰胺的摩尔比

Table 2 Mole ratio of reacted NO to melamine supported on 400-8(Mn-Ce)/SAC

Material balance	400-8(Mn-Ce)/SAC-5	400-8(Mn-Ce)/SAC-10	400-8(Mn-Ce)/SAC-15	400-8(Mn-Ce)/SAC-20
Amount of melamine on sample /×10^-4 mol	2.02	4.04	6.06	8.08
Breakthrough time(BTT) /h	4.20	8.80	13.80	18.50
Total amount of supplied net NO until BTT /×10^-4 mol	11.30	23.70	37.10	49.80
Ratio of reacted NO to supplied net NO /%	99.50	99.60	99.40	96.80
Amount of removed NO /× 10^-4 mol	11.20	23.60	36.90	48.20
Mole ratio of reacted NO to melamine on the catalyst	5.50	5.80	6.10	6.00

图 8 反应温度对melamine-SCR反应的影响

Fig. 8 Effect of reaction temperature on NOx conversion over 400-8(Mn-Ce)/SAC-10Reaction conditions: 0.1% NO, 8% O2, balance N2, space velocity = 6000 h-1

图 9 NO与O2浓度对melamine-SCR反应的影响

Fig. 9 Effect of (a) NO concentration and (b) O2 concentration on NOx conversion over 400-8(Mn-Ce)/SAC-10Reaction conditions: 0.01%~0.1% NO, 0~8% O2, balance N2, reaction temperature = 180℃, space velocity = 6000 h-1

图 10 空速对melamine-SCR反应的影响

Fig. 10 Effect of space velocity on NOx conversion over 400-8(Mn-Ce)/SAC-10Reaction conditions: 0.1% NO, 8% O2, balance N2, reaction temperature = 180℃

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球形活性炭担载MnO_x-CeO₂和三聚氰胺的低温脱硝行为研究

Low-temperature Removal of NO by Spherical Activated Carbon Loaded with MnO_x-CeO₂ and Melamine

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