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NOx是造成城市灰霾天气、光化学烟雾、大气酸沉降等一系列环境问题的根源之一[1]。SCR技术是工业上应用最为广泛的烟气脱硝技术[2]。低温SCR装置可置于除尘或脱硫装置之后而不加热烟气,使脱硝系统具有较低能耗且易于改装到锅炉烟气净化系统中[3]。另外,由于非电力行业工业窑炉排烟温度低,难以直接使用电力行业成熟的高温SCR脱硝工艺控制NOx的排放,而选择性非催化还原(selective non-catalytic reduction ,SNCR)氮氧化物净化效率较低,难以满足排放标准。因此,低温SCR脱硝技术将成为该领域主要脱硝工艺[4]。催化剂是制约低温SCR脱硝技术发展的核心问题,其活性直接影响SCR系统的整体效果[5]。锰铈系催化剂表现出Mn、Ce两种金属的性质,具有良好的低温SCR脱硝活性[6-7],是低温SCR催化剂领域热点,如催Mn-Ce/ASC[8]、Mn-Ce/ATP[9]、MnOx-CeO2 -Al2O3[10]和Ce-Mn/TiO2[11]等。
不同制备方法对催化剂的物理性质和化学性质均有不同影响。贺丽芳等[12]采用浸渍法、氨水共沉淀法和机械混合法制备了Mn-Ce/ZSM-5催化剂,并测试其脱硝性能。结果表明,采用氨水共沉淀法制备的Mn-Ce/ZSM-5催化剂显示出优越的SCR催化活性,不仅低温催化活性好、反应温度窗口宽,且热稳定性好。廖伟平等[13]采用浸渍法、沉淀沉积法及新型共沉淀法制得Mn-Ce/TiO2脱硝催化剂。结果表明,新型共沉淀法制备的Mn-Ce/TiO2催化剂有更高的低温活性。因此,催化剂制备方法不仅影响催化剂性能,且影响催化剂成本。
基于此,拟采用常用的3种催化剂制备方法——共沉淀法、浸渍法、溶胶凝胶法来制备Mn-Ce/TiO2,对比3种方法制备出催化剂的结构特点和活性,并分析制备过程和成本,以对比出催化剂的最佳制备方法,以期为锰基低温脱硝催化剂的制备提供参考。
3种制备方法对Mn-Ce/TiO2催化剂的性能影响及成本分析
Performance comparison and cost analysis of Mn-Ce/TiO2 catalyst made by different preparation methods
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摘要: 制备方法对催化剂的性能和成本有重要影响。选择共沉淀法、浸渍法和溶胶凝胶法制备Mn-Ce/TiO2催化剂,在90~220 ℃对比测试不同方法制得催化剂样品的低温SCR性能,利用BET、SEM、XRD、FT-IR、H2-TPR和NH3-TPD分析样品的物理化学性质,并对3种方法的实验室制备过程进行成本分析。结果表明:共沉淀法和浸渍法制备的催化剂低温SCR性能均较好,在反应温度为150 ℃的条件下,催化剂的脱硝效率达到100%;制备方法不仅会影响催化剂的比表面积、表面形貌,还会对催化剂的氧化还原能力和表面酸性位产生影响;成本由低到高依次为浸渍法、溶胶凝胶法、共沉淀法。3种方法制得同样质量的催化剂时,采用浸渍法所消耗的药剂最少,而且浸渍法制备过程最短,操作最简单。本研究可为锰基低温脱硝催化剂的制备提供参考。
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关键词:
- 低温SCR /
- Mn-Ce/TiO2 /
- 制备方法 /
- 催化剂性能 /
- 成本分析
Abstract: The preparation method has important influence on the performance and cost of the catalyst. Mn-Ce/TiO2 catalysts were prepared by co-precipitation method, impregnation method and sol-gel method, and the low-temperature SCR performances of the catalysts were tested at 90~220 ℃. The physical and chemical properties of the catalyst samples were analyzed by BET, SEM, XRD, FT-IR, H2-TPR and NH3-TPD. And the cost analysis of the catalysts prepared by the three methods was carried out. The results showed that the performances of the catalysts prepared by the co-precipitation method and the impregnation method both were better, and the dnirification efficiencies of the catalysts reached 100% at the reaction temperature of 150 ℃. The preparation method would not only affect the specific surface area and surface morphology of the catalyst, but also affect the redox capacity and surface acidity of the catalyst. The cost of the three methods from low to high was impregnation method, sol-gel method, coprecipitation method. When the three methods were used to prepare catalysts of the same quality , the impregnation method consumed the least amount of reagents, the impregnation method took the shortest time and the operation of which was the simplest.-
Key words:
- low-temperature SCR /
- Mn-Ce/TiO2 /
- preparation method /
- catalyst performance /
- cost analysis
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表 1 不同制备方法的催化剂的比表面积、孔容及平均孔径
Table 1. Specific surface area, pore volume and average pore size of the catalysts prepared by different methods
催化剂种类 比表面积/
(m2·g−1)微孔体积/
(cm3·g−1)平均孔径/
nmMn-Ce/TiO2(C) 80 0.44 22.19 Mn-Ce/TiO2(I) 74 0.85 46.19 Mn-Ce/TiO2(S) 78 1.58 81.40 表 2 不同制备方法的综合对比
Table 2. Comprehensive comparison of different preparation methods
制备方法 成本/元 制备过程 NO 转化率(90~220℃) 浸渍法 2.70 常温浸渍12 h+烘干12 h+焙烧500 ℃ 3 h 90℃,其NO转化率45%;120 ℃,NO转化率83%;
150 ℃以上,NO转化率100%。共沉淀法 32.11 水浴加热搅拌0.5 h+老化3 h+过滤洗涤2 h+
烘干12 h+焙烧500℃ 3 h。90 ℃,其NO转化率60%;120 ℃,NO转化率93%;
150 ℃以上,NO转化率100%。最优溶胶凝胶法 9.78 磁力搅拌器3 h+老化12~24 h+烘干12 h+焙烧500℃ 5 h 180 ℃,NO转化率69%;220 ℃,NO转化率91%。 -
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