SCR脱硝过程中NH4HSO4（(NH4)2SO4））形成与分解机理研究

论文总字数：30507字

摘 要

目前工业上主要采用的是选择性催化还原法（SCR）去除烟气中氮氧化物。本文主要针对SCR脱硝反应硫酸（氢）铵的形成和分解的机理进行研究。本文利用XRF、XRD等分析方法，对催化剂的各项性质进行了测定和表征。利用烟气分析、热重分析、傅里叶原位红外分析手段针对硫酸（氢）铵的形成和分解路径进行分析和推断。认为SCR反应机理是在250℃左右气相的氮氧化物与吸附态的氨气形成中间物种VONH₄ ，再生成氮气和水。ABS的形成机理是首先SO₂吸附在钒基催化剂表面V==O活性位形成中间物种VOSO₄，SO₂也被氧化为SO₃，再与VONH₄反应生成硫酸氢铵。纯ABS的分解步骤是在450℃一步形成H₂O、NH₃和SO₂，而V₂O₅/TiO2催化剂提高了ABS分解的温度窗口。类似的，纯AS的热分解过程分为三步，依次释放氨气、H₂O和SO₂，而负载在催化剂使分解的温度区间增大，氨气的脱除提前而SO₂的释放延缓。探究气相组成对ABS的沉积影响发现，一氧化氮、氨气由于占据活性位点，提高了二氧化硫在钒基催化剂表面的氧化温度窗口，与二氧化硫之间存在竞争吸附。而氧气的存在则通过对三价钒离子的重氧化作用，促进金属硫酸盐向三氧化硫的转化。而硫酸氢铵（ABS）沉积吸附在催化剂表面，覆盖住催化剂表面五氧化二钒的活性点位，对二氧化硫的吸附氧化起抑制作用。

关键词:选择性催化还原（SCR）；硫酸铵盐；形成；分解；机理

Study on the formation and decomposition mechanism of NH₄HSO₄ ((NH₄) ₂SO₄) in the process of SCR denitrification

by Zha rong

Supervised by. FAN Hong-mei

YANG Lin-jun

Abstract: This paper starting from the widely used method in the industry at present: the selective catalytic reduction method, aims at the side reaction of generating NH₄HSO₄ product and summarizes the mechanism and the influencing factors of the formation and decomposition of ABS, as well as the formation of metal sulfate in the catalyst active center in the previous study. This paper mainly uses flue gas analysis, thermal gravimetric analysis and in situ Fourier infrared analysis to speculate the path of the formation and decomposition of ABS and AS and to explore the factors that influence the reaction. The catalysts are characterized by XRF, XRD and other methods. The research is of great significance on the control of ammonium sulfate and the normal function of the SCR reaction system. The reaction mechanism of SCR is that the nitrogen oxides of gas phase reacts with the NH₃ of the adsorbed state ，forming an active intermediate at about 250 degrees C , and then forms the nitrogen and water. The formation mechanism of NH₄HSO₄ is that at first SO₂ adsorbs on the surface of vanadium based catalyst to form the intermediate product of metal sulfate（VOSO₄）when SO₂ also be oxidized to SO₃, and then SO₃ reacts with ammonia to produce ammonium hydrogen sulfate. The pure NH₄HSO₄ decomposes to H₂O, NH₃ and SO₂ at 450 degrees C, while the V₂O₅/TiO₂ catalyst increasing the temperature window of ABS decomposition. Similarly, the pure AS thermal decomposition process is divided into three steps, followed by the release of ammonia, H₂O and SO₂, but when loading on the catalyst the temperature range increases, advancing the removal of ammonia and postponing the release of SO₂. Researching on the influence of gas phase composition on the sedimentation of NH₄HSO₄, we finds that nitric oxide and ammonia occupies the active sites , improving the oxidation temperature window of the sulfur dioxide on vanadium catalyst surface, and has competitive adsorption behavior with sulfur dioxide. While by re oxidizing tetravalent vanadium ions, the existence of oxygen transforms metal sulfate sulfur oxidation to SO₃. Ammonium hydrogen sulfate (ABS) is deposited on the surface of the catalyst, covering the active site of pentad vanadium oxide on the surface of the catalyst, and inhibits the adsorption and oxidation of sulfur dioxide .

Key words: Selective catalytic reduction (SCR); ammonium sulfate; formation; decomposition；mechanism

目 录

SCR脱硝过程中NH₄HSO₄（(NH₄)₂SO₄））形成与分解机理研究 6

1 、绪 论 6

1.1研究背景及意义 6

1.2 SCR脱硝中AS（ABS）产生与分解机理的研究现状 7

1.2.1 SCR脱硝机理研究现状 7

1.2.2 脱硝过程中二氧化硫催化氧化机理研究现状 9

1.2.3 SCR脱硝过程中硫酸(氢)铵形成与分解机理研究进展 10

1.2.4 SCR脱硝过程中硫酸(氢)铵形成与分解的影响因素 11

1.2.5 SCR脱硝过程中硫酸(氢)铵生成控制措施 13

1.3 催化剂活性中心硫酸盐化研究进展 14

1.3.1 金属硫酸盐生成机理 14

1.3.2 金属硫酸盐生成的影响因素 14

1.4 本文研究内容和方法 14

1.5 本章小结 14

2、试验系统与方法 16

2.1 引言 16

2.2 实验装置与试剂 16

2.2.1实验装置系统 16

2.2.2实验试剂 17

2.3 试验仪器和设备 17

2.3.1烟气分析仪 17

2.3.2热重分析仪 17

2.3.3傅立叶原位红外光谱仪 17

2.4 催化剂样品的制备方法 18

2.4.1 新鲜催化剂样品制备 18

2.4.2 负载硫酸铵盐催化剂样品制备 18

2.5 催化剂样品的表征 19

2.5.1 BET比表面积测定 19

2.5.2 XRF分析 19

2.5.3 XRD分析 19

2.6 本章小结 20

3、 SCR脱硝中催化剂表面NH₄HSO₄（(NH₄)₂SO₄））形成机理研究 21

3.1催化剂样品制备及试验方法 21

3.1.1 负载型催化剂样品的制备 21

3.1.2 试验方法 21

3.2 NH₄HSO₄（(NH₄)₂SO₄））形成的原位红外实验 21

3.2.1 氧气对二氧化硫催化氧化反应影响的试验 21

3.2.2 SO₂ O₂→NH₃暂态原位红外实验 22

3.2.3 NH₃ O₂ SO₂稳态实验 23

3.2.4 NO对NH₄HSO₄生成及分解的影响 24

3.3 催化剂表面NH₄HSO₄（(NH₄)₂SO₄））形成路径推测 26

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