氧化还原沉淀法制备MnO2/MWCNTs催化剂及其低温SCR活性

doi:10.15541/jim20160146

摘要/Abstract

摘要：

先用十二烷基硫酸钠(SDS)对多壁碳纳米管(MWCNTs)进行表面改性, 然后采用氧化还原沉淀法制得一系列的MnO₂/MWCNTs催化剂。考察了催化剂在80~180℃的选择性催化还原(SCR)反应活性, 并通过BET、XRD、FESEM、TEM、XPS和H₂-TPR等表征手段对催化剂的结构及性能进行分析。结果显示, MnO₂/MWCNTs催化剂在空速210 L/(g_cat·h)和温度140~180℃条件下, 脱硝效率达到85%~100%, 这明显优于等体积浸渍法制备的催化剂的低温SCR催化活性, 且10% MnO₂/MWCNTs催化剂的活性最优。分析结果表明, MnO₂/MWCNTs催化剂中MnO₂以纳米片状均匀分散在多壁碳纳米管载体表面; 弱结晶性的结构和高价锰, 较高的表面吸附含氧量及较强的低温区氧化还原能力是10% MnO₂/MWCNTs催化剂具有优异低温SCR活性的原因。另外, 和MnO_x/MWCNTs催化剂相比, 10% MnO₂/MWCNTs催化剂表现出良好的抗水和抗硫性能。

关键词: 十二烷基硫酸钠, 选择性催化还原, 氮氧化物, 多壁碳纳米管, 锰氧化物

Abstract:

Pristine multiwalled carbon nanotubes (MWCNTs) were modified by sodium dodecyl sulfate (SDS). Afterwards, a series of MnO₂/MWCNTs were prepared via a redox method and used in selective catalytic reduction (SCR) of NO_x at 80-180℃. Structural properties and catalytic performance were investigated by specific surface area measurements (BET), X-ray diffraction (XRD), filed emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscope (XPS), and H₂ temperature-programmed reduction (H₂-TPR). The characterization results indicate that the nanoflaky MnO₂ highly disperse on MWCNTs. The results show that the low-temperature SCR activities of MnO₂/MWCNTs catalysts are 85%-100% at 140-180℃ at a weight hourly space velocity of 210 L/(g_cat·h), higher than that of catalyst fabricated via the wet impregnation method. The 10% MnO₂/MWCNTs catalyst displays first-rate SCR activity, which is attributed to its low crystallinity, high concentrations of Mn⁴⁺ and oxygen absorbtion onto the catalyst surface, as well as excellent reducibility. Additionally, compared to the MnO_x/MWCNTs catalyst, the 10% MnO₂/MWCNTs catalyst exhibits higher resistance to H₂O and SO₂.

Key words: sodium dodecyl sulfate, selective catalytic reduction, nitrogen oxide, multi-walled carbon nanotube, manganese oxide

中图分类号:

TB34

陈健, 郑玉婴, 张延兵, 邹海强, 卢秀恋. 氧化还原沉淀法制备MnO₂/MWCNTs催化剂及其低温SCR活性[J]. 无机材料学报, 2016, 31(12): 1347-1354.

CHEN Jian, ZHENG Yu-Ying, ZHANG Yan-Bing, ZOU Hai-Qiang, LU Xiu-Lian. Preparation of MnO₂/MWCNTs Catalysts by a Redox Method and Their Activity in Low-temperature SCR[J]. Journal of Inorganic Materials, 2016, 31(12): 1347-1354.

图/表 11

图1 MnO2/MWCNTs催化剂的制备示意图

Fig. 1 Schematic illustration for preparing MnO2/MWCNTs catalysts

图2 实验装置示意图

Fig. 2 Scheme of experiment apparatus^1. Air source; 2. Reducing valve; 3. Mass flowmeter; 4. Gas mixer; 5. Preheater; 6. Heater; 7. Sample; 8. Flue gas analyzer

图3 MnO2/MWCNTs及MnOx/MWCNTs催化剂的SCR活性

Fig. 3 SCR activity of MnO2/MWCNTs catalysts and MnOx/ MWCNTs catalyst^Reaction conditions: [NO]=[NH3]=400×10-6, [O2]=5%, N2 as balance gas, WHSV=210 L/(gcat·h), 200 mg sample

表1 原始MWCNTs、酸化MWCNTs及不同催化剂样品的比表面积、孔体积、平均孔径

Table 1 BET surface area, pore volumes and average pore size of pristine MWCNTs, acid-treated MWCNTs and different catalyst samples

Sample	S_BET/(m²·g^-1)	Pore volume/(cm³·g^-1)	Average pore size/nm
Pristine MWCNTs	72	0.15	8.1
Acid-treated MWCNTs	91	0.18	7.7
MnO_x/MWCNTs	69	0.15	9.0
6%MnO₂/MWCNTs	99	0.28	11.2
8%MnO₂/MWCNTs	100	0.29	11.6
10% MnO₂/MWCNTs	94	0.29	12.5
12% MnO₂/MWCNTs	111	0.31	11.3

图4 MnO2/MWCNTs及MnOx/MWCNTs催化剂的XRD图谱

Fig. 4 XRD patterns of MnO2/MWCNTs catalysts and MnOx/ MWCNTs catalyst^(a) Pristine MWCNTs; (b) 6% MnO2/MWCNTs; (c) 8% MnO2/MWCNTs; (d) 10% MnO2/MWCNTs; (e) 12% MnO2/MWCNTs; (f) MnOx/MWCNTs

图5 原始MWCNTs (a), MnOx/MWCNTs (b)及10% MnO2/MWCNTs (c, d)催化剂的FESEM照片

Fig. 5 FESEM images of (a) pristine MWCNTs, (b) MnOx/MWCNTs catalyst and (c, d) 10% MnO2/MWCNTs catalyst

图6 原始MWCNTs (a), MnOx/MWCNTs (b)及10% MnO2/MWCNTs (c)催化剂的TEM谱图和10% MnO2/MWCNTs (d)催化剂的HRTEM图像; (e) c中红色圆形区域的EDX谱图

Fig. 6 TEM images of (a) pristine MWCNTs, (b) MnOx/MWCNTs catalyst and (c) 10% MnO2/MWCNTs catalyst and HRTEM image of 10% MnO2/MWCNTs catalyst, as well as (e) EDX pattern of 10% MnO2/MWCNTs catalyst from the annular region in (c)

图7 10% MnO2/MWCNTs催化剂的Mn2p XPS谱图及不同催化剂样品的O1s XPS谱图

Fig. 7 Mn2p XPS spectra of 10% MnO2/MWCNTs catalyst (a) and O1s (b) spectra of different catalyst samples^(a) Mn2p; (b) O1s, (A) 10% MnO2/MWCNTs, (B) MnOx/MWCNTs

表2 10% MnO2/MWCNTs及MnOx/MWCNTs催化剂表面氧的相对含量

Table 2 Relative content of O for 10% MnO2/MWCNTs and MnOx/MWCNTs catalyst

Sample	O_S/%	O_L/%
10% MnO₂/MWCNTs	66.7	33.3
MnO_x/MWCNTs	61.1	38.9

图8 10% MnO2/MWCNTs(a)及MnOx/MWCNTs(b)催化剂的H2-TPR图

Fig. 8 H2 temperature-programmed reduction (H2-TPR) profiles for 10% MnO2/MWCNTs (a) and MnOx/MWCNTs (b) catalyst

图9 H2O和SO2对催化剂SCR活性的影响

Fig. 9 Effect of H2O and SO2 on the SCR activities of catalysts at 180℃^Reaction conditions: [NO]=[NH3]=400×10-6, [O2]=5%, [H2O]=5%, [SO2]=100×10-6, N2 as balance gas, WHSV=210 L/(gcat·h), 200 mg sample

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氧化还原沉淀法制备MnO₂/MWCNTs催化剂及其低温SCR活性

Preparation of MnO₂/MWCNTs Catalysts by a Redox Method and Their Activity in Low-temperature SCR

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