Study on alkali and alkaline earths poisoning characteristics for a commercial SCR catalyst
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摘要: 在实验室条件下对选择性催化还原(SCR)商业催化剂的碱(K)和碱土(Ca)中毒进行了模拟,并采用液氮吸附、扫描电镜、能谱分析、NH3-程序升温脱附、H2-程序升温还原等方法对催化剂中毒前后的物理化学性质变化进行了表征。结果表明, K和Ca的中毒没有破坏商业中温SCR催化剂孔的基本结构,但K和Ca的中毒使催化剂的比表面积和孔容减小。K和Ca的中毒在一定程度上改变了催化剂表面钒的价态,导致了钒的还原能力减弱,同时降低催化剂表面化学吸附氧。钾中毒和钙中毒使催化剂的表面酸量降低。钾和钙中毒造成中温SCR催化剂的脱硝活性降低,并且Ca中毒造成的催化剂活性降低要明显高于K中毒。Abstract: The poisoning of a commercial selective catalytic reduction (SCR) catalysts by alkali (K) and alkaline earths (Ca) has been simulated in the laboratory. The techniques of N2 adsorption, scanning electronic microscopy, X-ray photoelectron spectroscopy, NH3-temperature program desorption, H2-temperature program reduction were used to identify the changes of physical chemical characteristics of the catalysts before and after the simulated poisoning. The results indicated that the poisoning of K and Ca did not damage the basic pore structure of the SCR catalyst, but decreased the BET surface area and pore volume. The poisoning by K and Ca changed the chemical valence state of V and decreased the reducibility of V. The poisoning by K and Ca decreased the amount of chemically adsorbed oxygen on the catalyst surface as well as acidity of the catalysts. The poisoning by K and Ca lowered the SCR activity of the catalysts and the poisoning by Ca was more serious than K.
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表 1 不同催化剂的BET分析
Table 1 BET analysis of different catalysts
Catalyst type BET surface area A/(m2·g-1) Pore volume v/(cm3·g-1) Pore diameter d/nm F-SCR 94.68 0.3130 11.908 K-SCR 71.48 0.2888 14.665 Ca-SCR 87.96 0.2915 12.306 表 2 三种催化剂中V5+和V4+的含量
Table 2 Percentage of V4+ and V5+ in three kinds of catalysts
Catalyst Percentage w/% V5+/(V5++V4+) V4+/(V5++V4+) F-SCR 93.38 6.62 K-SCR 89.37 10.63 Ca-SCR 7.48 92.52 表 3 三种催化剂中晶格氧(Oa)和化学吸附氧(Ob)所占的百分含量
Table 3 Oxygen analysis of three kinds of catalysts
F-SCR K-SCR Ca-SCR Oa /% 58.89 62.12 59.64 Ob /% 41.11 37.88 40.36 表 4 催化剂中毒后效率下降百分数
Table 4 Efficiency decrease caused by catalyst poisoning
Catalyst Decrease in efficiency /% 250℃ 300℃ 350℃ 400℃ K-SCR(K/V=1) 44.6 10.8 12.8 5.5 K-SCR(K/V=3) 60 32.4 25.6 13.3 Ca-SCR(Ca/V=1) 41.5 14.9 11.6 9.1 Ca-SCR(Ca/V=3) 64.6 48.6 36.0 63.0 -
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