Influence of Zn in the iron ore sintering flue gas on the removal of NOx and dioxins by V2O5–WO3/TiO2 catalyst
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摘要: V2O5?WO3/TiO2（VWTi）催化劑可以同時脫除鐵礦燒結煙氣中的NOx和二噁英，但復雜的煙氣成分會導致催化劑失活。本文采用浸漬法對VWTi 催化劑進行ZnCl2、ZnO和ZnSO4中毒實驗。模擬燒結煙氣條件，研究了在VWTi催化劑表面負載不同形態Zn對其同時脫除NOx和二噁英（以氯苯作為模擬物）性能的影響，分析了中毒前后催化劑表面活性物質的理化性質，并對中毒催化劑開展了再生實驗。結果表明：不同Zn物種對VWTi催化劑同時脫除NOx和氯苯（CB）均具有失活作用。Zn物種會引起催化劑表面顆粒輕微團聚，表面酸性位點數量減少，表面V的還原性減弱，表面化學吸附氧比例，以及V5+和V4+的物質的量比值降低。再生實驗結果表明：酸洗可以在一定程度上恢復中毒催化劑的催化活性，但水洗不能恢復中毒催化劑的活性。研究發現Zn鹽中毒作用機理為：Zn2+與催化劑表面酸性位點V=O和V?OH反應形成V?O?Zn，對NH3與CB的吸附產生不利影響，造成催化劑中毒失活，ZnSO4中的
${\rm{SO}}_4^{2-} $ 可以為NH3和CB的吸附轉化提供新的酸性位點，減輕中毒效果，ZnCl2中的Cl?會在反應后產生副產物HCl，造成催化劑表面更多活性位點中毒，加深中毒效果。-
關鍵詞:
- V2O5–WO3/TiO2 /
- Zn物種 /
- 中毒 /
- NOx /
- 二噁英
Abstract: Iron ore sintering is a process in which fuel, flux, and iron ore powders are mixed and sintered into a block under incomplete melting conditions. The flue gas from iron ore sintering process is one of the largest sources of nitrogen oxide (NOx) and dioxin emissions in industries. The V2O5–WO3/TiO2 (VWTi) catalyst can simultaneously remove NOx and dioxins, but the presence of the complex flue gas results in the deactivation of the catalysts. In response to this challenge, this study carried out experiments for ZnCl2, ZnO, and ZnSO4 poisoning over the VWTi catalyst via wet impregnation method. The effects of the different Zn species on the simultaneous removal of NOx and dioxins (chlorobenzene was used as the simulant for dioxins) by the VWTi catalyst were studied under simulated conditions of the iron ore sintering flue gas. The surface physicochemical properties of the fresh and poisoned catalysts were characterized to reveal the deactivation mechanism, and the regeneration experiments of the poisoned catalysts were investigated. Results showed that deactivation through catalytic denitrification and chlorobenzene (CB) catalytic degradation processes could be observed in different Zn-containing catalysts. The poisoning effect was more obvious with the increase of Zn content, and the effects of deactivation were as follows: ZnCl2>ZnO>ZnSO4. Results from physical and chemical analyses indicated that Zn species had a significant influence on the chemical environment of the active substances on the surface of the catalysts. Zn species caused a slight agglomeration of particles on the surface of the catalysts, a decrease in the number of surface acid sites, a reduction in the reducibility of surface V species, and a decrease in the chemisorbed oxygen ratio and the molar ratio of n(V5+)/n(V4+). The regeneration experiments confirmed that employing the dilute sulfuric acid solution washing method was effective for recovering the catalytic activity, whereas the water washing method failed to restore the catalytic activity. The mechanism of Zn salt poisoning is as follows: Zn2+ reacts with the acid sites V=O and V?OH on the surface of the catalyst to form V?O?Zn, which adversely affects the adsorption of NH3 and CB, resulting in the catalyst poisoning and deactivation. The${\rm{SO}}_4^{2-} $ in ZnSO4 provides a new acidic site for the adsorption and transformation of NH3 and CB alleviating the poisoning effect. The Cl? in ZnCl2 produces HCl as a by-product after the reaction, resulting in more active sites poisoning on the surface of the catalyst and deepening the poisoning effect.-
Key words:
- V2O5–WO3/TiO2 /
- Zn species /
- poisoning /
- NOx /
- dioxin
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圖 2 新鮮催化劑與Zn2+中毒催化劑的脫硝活性（a）和CB降解率（b）
Figure 2. Denitrification (a) and chlorobenzene degradation (b) of activity of fresh and Zn2+-poisoned catalysts
圖 3 新鮮催化劑和Zn2+中毒催化劑XRD圖譜
Figure 3. X-ray diffraction spectra of fresh and Zn2+-poisoned catalysts
圖 4 新鮮催化劑和Zn2+中毒催化劑N2吸附曲線
Figure 4. N2 adsorption curves of fresh and Zn2+-poisoned catalysts
圖 5 （a）Fresh catalyst，（b）ZC2，（c）ZO2 and （d）ZS2 的掃描電鏡圖譜
Figure 5. Scanning electron microscopy images of (a) fresh (b) ZC2, (c) ZO2, and (d) ZS2 catalysts
圖 6 新鮮催化劑和Zn2+中毒催化劑NH3?TPD圖譜
Figure 6. NH3?TPD profiles of fresh and Zn2+-poisoned catalysts
圖 7 新鮮催化劑和Zn2+中毒催化劑H2?TPR圖譜
Figure 7. H2?TPR profiles of fresh and Zn2+?poisoned catalysts
圖 8 不同催化劑O1s XPS圖譜
Figure 8. X-ray photoelectron spectroscopy (XPS) spectra of O1s in different catalysts
圖 10 新鮮催化劑和Zn2+中毒催化劑拉曼光譜圖
Figure 10. Raman spectra of fresh and Zn2+-poisoned catalysts
圖 11 再生催化劑脫硝（a）和CB降解活性（b）
Figure 11. Denitrification activity (a) and CB degradation activity (b) of the regenerated catalysts
圖 12 WVTi催化劑 ZnO、ZnCl2 和 ZnSO4中毒機理圖
Figure 12. Schematic of the mechanism of poisoning of the WVTi catalyst by ZnO, ZnCl2, and ZnSO4
表 1 新鮮催化劑和Zn2+中毒催化劑的BET表面積、孔容積和孔徑
Table 1. Brunauer–Emmett–Teller surface area, pore volume, and pore size of fresh and Zn2+-poisoned catalysts
Samples Surface area / (m2·g?1) Pore volume / (cm3·g?1) Pore size / nm Fresh 38.25 0.185 19.38 ZC2 37.35 0.179 19.19 ZO2 37.44 0.181 19.39 ZS2 33.26 0.172 20.45 
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表 2 新鮮催化劑和Zn2+中毒催化劑V XPS結果
Table 2. X-ray photoelectron spectroscopy results of V in fresh and Zn2+-poisoned catalysts
V2p3/2 Fresh ZC2 ZO2 ZS2 Ebv/eV ω/% Ebv/eV ω/% Ebv/eV ω/% Ebv/eV ω/% V3+ 515.3 6.22 515.4 8.25 515.2 7.14 515.4 5.88 V4+ 516.5 31.56 516.5 40.36 516.5 38.09 516.4 35.29 V5+ 517.4 62.21 517.2 51.37 517.3 54.76 517.1 58.82 V5+/V4+ 1.97 1.27 1.43 1.67
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表 3 中毒催化劑再生前后XRF結果
Table 3. X-ray fluorescence results of the poisoned catalysts, before and after regeneration
% Samples Mass content of different elements/% Ti Si Al W S V Ca Zn Fresh 42.43 6.11 2.00 2.11 0.84 1.08 1.37 — ZC2 41.8 5.66 1.88 2.05 0.969 1.07 1.35 1.03 ZC2?W 43.41 5.89 1.91 2.14 0.314 1.08 1.20 0.78 ZC2?A 44.87 5.95 1.75 2.17 0.32 0.75 1.18 0.06 ZO2 42.44 5.80 1.91 2.06 0.756 1.08 1.35 1.27 ZO2?W 43.62 5.86 1.94 2.14 0.305 1.08 1.22 0.98 ZO2?A 44.68 5.91 1.73 2.22 0.31 0.77 1.20 0.05
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