Cr负载V2O5-WO3/TiO2催化剂的低温NH3-SCR脱硝活性

doi:10.7503/cjcu20190091

摘要/Abstract

摘要：

采用浸渍法制备了一系列不同Cr负载量的CrO_x-V₂O₅-WO₃/TiO₂催化剂, 研究了Cr改性对该催化剂脱硝活性及抗硫性能的影响. 结果表明, Cr的引入使V₂O₅-WO₃/TiO₂催化剂的低温NO_x去除效果和抗硫性能显著提升. Cr的负载量为3%(以Cr₂O₃计算质量分数)时, 催化剂具有最佳的低温脱硝活性和N₂选择性. 结构表征结果表明, 改性催化剂中Cr元素主要以Cr³⁺形式存在, Cr的引入使催化剂的氧化性能明显提升, 并使表面弱酸位点、强酸位点和催化剂表面吸附氧数量增多. XPS分析结果表明, Cr能使催化剂中V⁵⁺/V⁴⁺比例降低, 促进催化剂中自由电子的迁移. In situ DRIFTs表征结果显示, Cr的引入能促进NO与吸附在Brönsted酸位点上的NH₃在低温条件下反应, 从而使催化剂具有更好的低温脱硝活性. UV-Vis光谱分析结果表明, CrO_x负载量提高会显著增加高价态Cr的烧结聚集. 同时, 提出了一种选择性催化还原(SCR)反应中Cr-V协同催化的机理.

关键词: 选择性催化还原, Cr改性, 低温脱硝活性

Abstract:

A series of different contents of Cr loading catalysts was prepared by impregnation method. De-NO_x activity and SO₂ resistance of Cr doped catalysts were measured and the result shows that the introduction of Cr promotes both of them obviously. When the amount of loading Cr(calculate as Cr₂O₃) is 3%, the catalyst possesses the best low-temperature De-NO_x activity and good N₂ selectivity. Analysis of catalyst characterization shows that the main valence state of chromium in Cr doped catalyst is Cr³⁺. Cr enhances the oxidation of catalyst while increasing the amount of weak, strong acid site and surface active oxygen. The XPS result indicates that loading of Cr decreases the ratio of V⁵⁺/V⁴⁺ and leads a result of the free electrons formed in non-stoichiometric V. The In situ DRIFTs shows Cr loading facilitates the reaction of NO and NH₃ absorbed on Brönsted acid site at low temperature and promote the NH₃-selective catalytic reduction activity.

Key words: NH₃-selective catalytic reduction, Cr doped catalyst, Low temperature De-NO_x activity

中图分类号:

O643.3

TrendMD:

李春晓, 李坚, 梁文俊, 梁全明. Cr负载V₂O₅-WO₃/TiO₂催化剂的低温NH₃-SCR脱硝活性. 高等学校化学学报, 2019, 40(7): 1447.

LI Chunxiao, LI Jian, LIANG Wenjun, LIANG Quanming. Low Temperature NH₃-SCR Activity of Cr Doped V₂O₅-WO₃/TiO₂ Catalyst^†. Chem. J. Chinese Universities, 2019, 40(7): 1447.

图/表 11

Table 1 Specific surface area, pore volume and average pore size of the catalysts

Catalyst	Specific surface area/(m²·g^-1)	Pore volume/(cm³·g^-1)	Average pore size/nm
3V6W/TiO₂	78.857	0.380	17.533
1Cr3V6W/TiO₂	66.756	0.325	17.944
3Cr3V6W/TiO₂	66.182	0.312	18.028
5Cr3V6W/TiO₂	65.287	0.310	18.523
7Cr3V6W/TiO₂	63.937	0.301	18.729
9Cr3V6W/TiO₂	62.172	0.293	19.239

Fig.1 N2 adsorption-desorption isotherms and pore size distributions(inset) of 3Cr3V6W/TiO2(A) and 3V6W/TiO2(B)

Fig.2 XRD patterns of the catalystsa. 3V6W/TiO2; b. 1Cr3V6W/TiO2; c. 3Cr3V6W/TiO2;d. 5Cr3V6W/TiO2; e. 7Cr3V6W/TiO2; f. 9Cr3V6W/TiO2.

Fig.3 H2-TPR profiles of the catalystsa. 3V6W/TiO2; b. 1Cr3V6W/TiO2; c. 3Cr3V6W/TiO2;d. 5Cr3V6W/TiO2; e. 7Cr3V6W/TiO2; f. 9Cr3V6W/TiO2.

Fig.4 NH3-TPD profiles of the catalystsa. 3V6W/TiO2; b. 1Cr3V6W/TiO2; c. 3Cr3V6W/TiO2;d. 5Cr3V6W/TiO2; e. 7Cr3V6W/TiO2; f. 9Cr3V6W/TiO2.

Fig.5 XPS spectra of the catalysts(A) 3Cr3V6W/TiO2, O1s; (B) 3Cr3V6W/TiO2, V2p; (C) 3V6W/TiO2, O1s; (D) 3V6W/TiO2, V2p; (E) 3Cr3V6W/TiO2, Cr2p.

Table 2 Binding energies and surface atomic concentrations of O, Cr and V for the prepared catalysts determined from deconvoluted XPS spectra*

Catalyst	E_b/eV						Surface atomic concentration			V⁵⁺/V⁴⁺	O_β/O_α	Cr⁶⁺/Cr³⁺
Catalyst	V₂_p		Cr₂_p		O₁_s		O	V	Cr	V⁵⁺/V⁴⁺	O_β/O_α	Cr⁶⁺/Cr³⁺
3V6W/TiO₂	516.4	517.1	—	—	530.0	531.6	13.52	1.00	—	1.401	0.127
3Cr3V6W/TiO₂	516.4	517.1	575.8	579.5	529.9	531.4	16.06	0.91	1.09	0.312	0.425	0.230

Fig.6 In situ DRIFTs spectra of catalysts(A) 3V6W/TiO2 adsorbed NH3 in 1%NH3-N2 and desorbed in N2; (B) 3Cr3V6W/TiO2 adsorbed NH3 in 1%NH3-N2 and desorbed in N2; (C) 3V6W/TiO2 adsorbed NH3 in 1%NH3-N2 then reacted in 0.1%NO+5%O2/N2; (D) 3Cr3V6W/TiO2 adsorption in 1%NH3-N2 then reacted in 0.1%NO+5%O2-N2.

Fig.7 UV-Vis spectra of catalysts(A) 200—800 nm; (B) 350—800 nm(3V6W/TiO2 sample as background). a. 3V6W/TiO2;b. 1Cr3V6W/TiO2; c. 3Cr3V6W/TiO2; d. 5Cr3V6W/TiO2; e. 7Cr3V6W/TiO2; f. 9Cr3V6W/TiO2.

Fig.8 NH3-SCR activity(A), N2 selective(B) and SO2 resistance(C) of catalystsa. 1Cr3V6W/TiO2; b. 3Cr3V6W/TiO2; c. 3V6W/TiO2; d. 5Cr3V6W/TiO2; e. 7Cr3V6W/TiO2; f. 9Cr3V6W/TiO2.

Fig.9 Cr promoting dehydrogenation of NH3 under E-R mechanism

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Cr负载V₂O₅-WO₃/TiO₂催化剂的低温NH₃-SCR脱硝活性

Low Temperature NH₃-SCR Activity of Cr Doped V₂O₅-WO₃/TiO₂ Catalyst^†

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