水热法制备氧化铬及其常温低浓度一氧化氮催化性能

doi:10.15541/jim20160019

摘要/Abstract

摘要：

以十六烷基三甲基溴化铵(CTAB)为模板剂, 氨水为沉淀剂, 通过水热法并焙烧处理合成氧化铬催化剂。采用X射线衍射分析(XRD)、傅里叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)和透射电镜(TEM)等技术对催化剂的物化性质进行了表征, 并考察常温不同NO初始浓度下氧化铬催化剂的NO氧化性能。结果表明: 在空速为60000 mL/(g·h)和NO浓度为1×10^-6的条件下, 100℃水热温度制备的Cr-100催化剂表现出最优的性能, 常温下NO消除率高达90%以上并保持120 h, 其优异的常温催化性能与催化剂表面较高的Cr⁶⁺/Cr³⁺摩尔比有关。研究结果表明: 催化剂的失活主要是由于硝酸根在催化剂表面的累积而导致催化剂活性中心被覆盖, 低浓度下能减缓硝酸根的积累。

关键词: 水热法, 常温, 失活, 氧化铬

Abstract:

The chromic oxide catalysts were synthesized by hydrothermal method using CTAB as surfactant and NH₃·H₂O as precipitant. Physiochemical properties of these catalysts were characterized by X-ray diffraction (XRD), Fourier Transform lufrared specfroscopy (FT-IR), X-ray photoelectron spectroscope (XPS), and transmission electron microscope (TEM). The catalytic NO removal performances for different NO concentrations at room temperature was also investigated. It was shown that under the conditions of space velocity of 60, 000 mL/(g·h) and NO concentration of 1×10^-6, sample of Cr-100 exhibited the best catalytic performance, which maintained 120 h as removal ratio of NO more than 90%. This excellent catalytic performance could be attributed to the surface ions ratio of Cr⁶⁺/Cr³⁺. The FT-IR analysis indicated that catalyst deactivation was due to the active sites of chromic oxide occupied by nitrates, consistent with the results of XPS. Furthermore, the activity tests in different conditions demonstrated that low NO concentration could slow down the rate of nitrate accumulation and prolong the catalyst lifetime.

Key words: hydrothermal, ambient temperature, deactivation, chromic oxide

中图分类号:

X511

吴美健, 高振源, 袁静, 赵昆峰, 蔡婷, 杨玲, 张涛, 何丹农. 水热法制备氧化铬及其常温低浓度一氧化氮催化性能[J]. 无机材料学报, 2016, 31(11): 1191-1197.

WU Mei-Jian, GAO Zhen-Yuan, YUAN Jing, ZHAO Kun-Feng, CAI Ting, YANG Ling, ZHANG Tao, HE Dan-Nong. Hydrothermal Fabrication and Catalytic Performance of Chromium Oxide for Low-concentration NO Oxidation at Ambient Temperature[J]. Journal of Inorganic Materials, 2016, 31(11): 1191-1197.

图/表 9

图1 不同水热温度下制备的催化剂XRD图谱

Fig. 1 XRD patterns of catalyst synthesized at various hydrothermal temperatures(a) Cr-160; (b) Cr-140; (c) Cr-120; (d) Cr-100U; (e) Cr-100; (f) Cr-80

图2 两种水热温度下制备的催化剂的透射电镜照片

Fig. 2 TEM (a, c) and HETEM (b, d) images of the chromium oxide catalysts synthesized at different hydrothermal temperatures(a) Cr-100; (b) Cr-100; (c) Cr-160; (d) Cr-160

图3 不同水热温度下制备的催化剂与NO消除测试失活后催化剂的Cr2p的XPS图谱

Fig. 3 XPS spectra of Cr2p of fresh samples prepared at different hydrothermal temperatures and catalyst after NO removal test(a) Cr-100; (b) Cr-100U; (c) Cr-80; (d) Cr-160

图4 Cr-100的NO消除性能测试前后O1s的XPS图谱

Fig. 4 XPS spectra of O1s for fresh and Cr-100 after NO removal test(a) Cr-100; (b) Cr-100U

表1 不同水热温度下制备的催化剂与经NO消除性能测试失活后的催化剂的物理化学性质

Table 1 Properties and XPS result of fresh samples prepared at different hydrothermal temperatures and catalyst after NO removal test

Samples	Cr⁶⁺/Cr³⁺	Cr/O	N/Cr	d_XRD/nm
Cr-80	0.37	0.22	-	26.4
Cr-100	0.64	0.32	0	20.7
Cr-100U	0.52	0.34	0.23	22.0
Cr-160	0.23	0.19	-	37.6

图5 Cr-100催化剂的NO消除性能测试前后的红外光谱

Fig. 5 FT-IR spectra of Cr-100 catalysts before and after NO removal test

图6 (a)不同水热温度下制备催化剂的NO消除率和(b) Cr-100催化NO生成NO2的量

Fig. 6 (a) The stability tests of NO oxidation at ambient temperature over chromic catalysts and (b) NO2 concentration catalyzed by Cr-100 catalyst(Reaction conditions: mass of catalyst = 0.25 g, total flow rate =500 mL/min, GHSV = 120000 mL/(g·h), NO concentration=5×10-6, temperature=30℃)

图7 不同NO初始浓度对Cr-100催化剂的活性影响

Fig. 7 Effect of different initial NO concentrations on NO removal over the Cr-100 catalyst(Reaction conditions: mass of Cr-100 catalyst = 0.25 g, total flow rate = 500 mL/min, GHSV = 120000 mL/(g·h), NO concentration = 2×10-6, 5×10-6, 10×10-6, temperature=30℃)

图8 Cr-100催化剂的NO常温消除寿命测试

Fig. 8 The stability tests of NO removal over Cr-100 catalyst(Reaction conditions: mass of Cr-100 catalyst = 0.5 g, total flow rate: = 500 mL/min, GHSV = 60000 mL/(g·h), NO concentration = 1×10-6 , temperature = 30℃)

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