Study of the catalytic denitrification activity of a modified steelmaking sludge catalyst
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摘要: 選擇性催化還原技術是工業煙氣脫硝技術中最常用的煙氣脫硝方法。但催化劑的制備過程較為復雜，并且制備成本較高。本文以鋼鐵企業在生產過程中產生的煉鋼污泥作為原料，采用焙燒改性、硫酸改性和硫酸–焙燒改性三種不同方法對其進行處理，制備了一種用于選擇性催化還原氮氧化物的新型催化劑。采用比表面積分析法（BET）、掃描電鏡分析（SEM）、X射線衍射分析（XRD）、X射線熒光光譜分析（XRF）和NH3程序升溫脫附分析（NH3-TPD）等表征手段，對改性前后煉鋼污泥催化劑物理化學性質的變化進行分析研究。結果表明：催化劑的主要活性組分為Fe、Mn、V、Ti；焙燒改性對催化劑活性具有一定的提升效果，可以使催化劑中的Fe3O4轉化為具有更好脫硝活性的α-Fe2O3；硫酸改性后的催化劑具有優異的催化活性，300 °C時可以達到88.5%的脫硝效率；硫酸改性改變了催化劑表面形貌，減小了晶粒尺寸，生成了大量的硫酸鹽物種，給催化劑表面提供了更多酸性位點，從而促進催化性能的提升。該研究為低成本脫硝催化劑的開發提供了基礎，促進了冶金工業的清潔生產。Abstract: The most commonly used method for industrial flue gas denitrification is selective catalytic reduction (SCR). However, the catalyst preparation is complex and expensive. The iron and steel industry produces large amounts of waste containing metal oxides that can be used as active catalytic components for SCR of nitrogen oxides. In this study, a novel catalyst for SCR of nitrogen oxides was prepared by roasting, sulfuric acid, and sulfuric acid-roasting modification of steelmaking sludge, which is used as the raw material. The physical and chemical properties of the catalysts from steelmaking sludge before and after modification were analyzed using Brunauer-Emmett-Teller analysis, scanning electron microscopy, X-ray diffraction, X-ray fluorescence, and temperature-programmed desorption of ammonia. It has been revealed that Fe, Mn, V, and Ti are the main active groups of the catalyst. Calcination can transform Fe3O4 to α-Fe2O3 with better denitrification activity, thus improving the catalyst reactivity. A high calcination temperature can cause a collapse of the pore structure of the catalyst, thereby decreasing the surface area and active sites and ultimately reducing the catalytic activity. The catalyst modified at the optimum calcination temperature of 400 °C has the highest catalytic activity at 350 °C and a denitrification efficiency of 57.6%. The sulfuric acid-modified catalyst has excellent catalytic activity. Sulfuric acid impregnation changes the surface morphology of the catalyst, reduces the grain size, generates numerous sulfate species, provides more acidic sites on the catalyst surface, and promotes catalyst performance. The 9 mol·L?1 sulfuric acid-modified catalyst has the highest denitrification efficiency at 300 °C. Compared with the unmodified catalyst, the denitrification efficiency significantly increased from 22.9% to 88.5%. Conversely, a denitrification efficiency of 72.9% is measured for the catalyst modified by sulfuric acid and roasting modification, which is lower than that of the sulfuric acid-modified catalyst at 300 °C. This may be explained by the fact that sulfuric acid and roasting modification causes not only structural changes in the catalyst but also the decomposition of the generated sulfate species, thereby leading to catalytic efficiency reduction. This work shows a feasible preparation of a low-cost SCR catalyst for denitrification by roasting and acid modification using steelmaking sludge as the raw material, provides a theoretical basis for developing low-cost denitrification catalysts using metallurgical solid wastes and promotes clean production in the metallurgical industry.
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圖 2 焙燒改性SS催化劑的脫硝性能
Figure 2. Denitrification performance of the SS catalysts modified by roasting
圖 3 硫酸改性SS催化劑的脫硝性能
Figure 3. Denitrification performance of the SS catalysts modified by sulfuric acid
圖 4 不同改性方式對SS催化劑脫硝性能的影響
Figure 4. Effect of different modification methods on denitration denitrification performance of the SS catalysts
圖 5 SS催化劑在200～450 °C時將NO氧化為NO2的轉化率
Figure 5. Conversion rates of the SS catalysts to oxidize NO to NO2 at 200–450 °C
圖 6 催化劑掃描電鏡分析譜圖. (a)SS; (b)SS-C-600; (c)SS-A-5; (d)SS-A-C
Figure 6. SEM analysis spectrum of catalysts: (a)SS; (b)SS-C-600; (c)SS-A-5; (d)SS-A-C
圖 7 (a)催化劑的氮氣吸附–脫附等溫線；(b)基于BJH法計算的孔徑分布
Figure 7. (a) Nitrogen adsorption–desorption isotherms of the catalysts; (b) pore size distributions calculated using the BJH method
圖 10 (a)SS催化劑隨時間變化NOx的吸附情況；(b) SS催化劑隨溫度變化NOx的脫附情況
Figure 10. (a) NOx adsorption of the SS catalysts with time; (b) NOx desorption of SS catalysts with temperature
表 1 催化劑元素分析結果（質量分數）
Table 1. Elemental analysis of the catalysts
% Sample Fe2O3 CaO MgO SiO2 ZnO Al2O3 MnO TiO2 V2O5 SOx Sum SS 69.84 19.42 4.16 1.53 1.20 0.56 0.27 0.13 0.11 0.56 97.78 SS-C-600 67.37 18.53 7.23 1.80 0.98 0.74 0.25 0.11 0.10 0.74 97.85 SS-A-5 58.70 15.29 3.32 1.25 0.86 0.40 0.23 0.12 0.10 18.24 98.50 SS-A-C 58.72 16.51 3.06 1.27 0.94 0.45 0.21 0.11 0.09 16.85 98.21 
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表 2 催化劑的BET分析結果
Table 2. BET analysis results of the catalysts
Sample SBET/(m2·g–1) Pore volume/(cm3·g–1) Pore size/nm SS 21 0.063181 11.946 SS-C-600 6 0.046535 32.981 SS-A-5 12 0.055125 18.165 SS-A-C 11 0.07672 26.777
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表 3 催化劑的NH3脫附量（基于峰面積計算）
Table 3. NH3 desorption amounts of catalysts (based on peak area calculation)
Sample Weak acid sites (a.u.) Medium strong and strong
acid sites (a.u.)Total (a.u.) SS 86.87 241.82 328.69 SS-C-600 84.89 145.73 230.62 SS-A-5 113.08 284.70 397.78 SS-A-C 96.92 176.18 273.10
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