超声辅助合成纳米氧化锰及其低浓度NO去除性能研究

doi:10.15541/jim20180209

摘要/Abstract

摘要：

通过超声辅助的工艺, 利用氧化还原法制备出多价态纳米MnO_x。通过调节超声时间、KMnO₄浓度、烘干温度、反应溶液pH, 探索MnO_x的最佳合成条件。结果表明: 超声时间20 min, 高锰酸钾浓度0.5 mol/L, 烘干温度80 ℃, 反应溶液pH=7的条件下, 合成的样品MnO_x表现出最佳的催化性能, 对100%的NO去除率可持续15 h。采用X射线衍射分析(XRD)、N₂-吸脱附测试、扫描电镜(SEM)、透射电镜(TEM)等技术考察最优催化剂MnO_x的结构和形貌, 借助X射线光电子能谱(XPS)和傅里叶红外分析(FT-IR)研究最优催化剂MnO_x对NO去除的催化氧化机理以及催化剂的失活机制。结果表明, 三维贯穿的多级孔结构, 花瓣状的形貌和弱晶化的晶体结构有利于气体吸附和传输。多价态Mn和氧空位的存在促进了NO和O₂的吸附和激活, 因此最优样品MnO_x表现出优异的NO的常温催化氧化。

关键词: MnO_x, 低浓度NO, 超声, 纳米材料, 氧化

Abstract:

The varied-valence nanocatalyst MnO_x was prepared using the oxidation-reduction method under ultrasonic. The optimal synthetic conditions of MnO_x were explored by adjusting the ultrasonic time, concentration of reaction precursor, drying temperature, and pH of reaction solution. The results indicated that the optimal sample MnO_x was synthesized under the condition of ultrasonic time of 20 min, 0.5 mol/L KMnO₄, drying temperature of 80 ℃ and pH=7, which showed the super catalytic performance and the time of 100% NO removal rate was as high as 15 h at room temperature. The structure and morphology of the optimal catalyst MnO_x were investigated by XRD, N₂-adsorption-desorption analysis, SEM and TEM. Besides, XPS and FT-IR were also applied to explore the catalytic oxidation process of NO removal and the deactivation mechanism of the optimal sample MnO_x. It is believed that the interpenetrating and hierarchal pore, the petaloid morphology and weak crystallization structure contribute to the gas adsorption and transmission. The presence of varied-valence Mn and oxygen vacancy can improve the adsorption and activation of NO and O₂, thus, enhancing the NO catalytic removal on the optimal catalyst MnO_x at room temperature.

Key words: MnO_x, low concentration NO, ultrasonic, nano materials, oxidation

中图分类号:

TQ174

龚云,刘艳,顾萍,朱钰方,周晓霞. 超声辅助合成纳米氧化锰及其低浓度NO去除性能研究[J]. 无机材料学报, 2019, 34(2): 186-192.

GONG Yun, LIU Yan, GU Ping, ZHOU Xiao-Xia. Synthesis of Nano Manganese Oxide with Assistance of Ultrasonic for Removal of Low Concentration NO[J]. Journal of Inorganic Materials, 2019, 34(2): 186-192.

图/表 8

图1 MnOx样品合成工艺参数对NO催化氧化性能的影响

Fig. 1 Effect of process parameters of the sample MnOx on the NO catalytic removal performance (a) Ultrasonic time; (b) Reactants concentration; (c) Dry temperature; (d) pH

图2 样品MnOx-20-0.5-80-7煅烧前后的XRD图谱(a)和N2吸附-脱附曲线与孔径分布曲线(b)

Fig. 2 XRD patterns of MnOx-20-0.5-80-7 before and after calcination (a) and corresponding N2 adsorption-desorption curves and the distribution of pore size (b)

图3 MnOx-20-0.5-80-7的SEM (a)~(b)和TEM (c)照片以及相应的电子衍射图(d)

Fig. 3 SEM (a-b) and TEM (c) images and the corresponding (d) SAED pattern of MnOx-20-0.5-80-7

图4 催化反应前后MnOx-20-0.5-80-7的XPS谱图

Fig. 4 XPS spectra of the sample MnOx-20-0.5-80-7 before and after catalytic test(a) Mn2p3/2, before; (b) Mn2p3/2, after; (c) O1s, before; (d) O1s, after

表1 MnOx-20-0.5-80-7在NO催化反应前后XPS数据

Table 1 XPS data of catalyst MnOx-20-0.5-80-7 before and after the NO removal test

Element	Phase	Before test		After test
Element	Phase	Binding energy/eV	Percentage/%	Binding energy/eV	Percentage/%
Mn-surface	Mn²⁺	641.2	4.8	641.1	4.1
	Mn³⁺	642.5	26.7	642.5	37.6
	Mn⁴⁺	643.5	66.5	643.5	58.3
Mn-etch 10 s	Mn²⁺	640.9	13.5	640.8	10.8
	Mn³⁺	642.1	54.0	642.1	56.5
	Mn⁴⁺	644.3	32.5	644.3	32.7
O-surface	O_lat	530.1	54.5	530.1	64.0
O-surface	O_ads	531.5	45.5	531.8	36.0
O-etch 10 s	O_lat	530.1	78.5	530.0	70.2
O-etch 10 s	O_ads	531.5	21.5	531.5	29.8

图5 催化剂MnOx-20-0.5-80-7对低浓度NO常温去除性能评价(进口气体: [NO]=10 cm3/m3, [O2]=21%, 载气N2, 25 ℃, 空速120000 mL•h-1•g-1)

Fig. 5 Catalytic performance of the sample MnOx-20-0.5-80-7 on low-concentration NO removal ratio at room temperature (Reaction conditions: [NO]=10 cm3/m3, [O2]=21%, N2, 25 ℃ and GHSV = 120000 mL•h-1•g-1)

图6 MnOx-20-0.5-80-7催化反应前后的FT-IR谱图

Fig. 6 FT-IR spectra of MnOx-20-0.5-80-7 before and after catalytic test

图7 在材料MnOx可能发生的NO催化氧化机理

Fig. 7 The possible catalytic process of MnOx toward NO oxidation

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