Abstract:

At present, the problem of high CO concentration in the flue gas emission occurs during the flexible peaking process of coal-fired power plants, which affects the denitrification performance of the vanadium-titanium catalyst in the denitrification system. In this study, vanadium-titanium catalysts and Sb-modified vanadium-titanium catalysts were prepared by ultrasonic impregnation, and the effect of CO on the NH₃-SCR denitrification performance of vanadium-titanium catalysts was investigated, while the mechanism of Sb-modification in improving the anti-CO poisoning performance of vanadium-titanium catalysts was also explored. The catalyst samples were characterized and analyzed by N₂ adsorption and desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and in-situ infrared diffuse reflection (in-situ DRIFT). The results showed that the presence of CO deteriorated the NH₃-SCR denitrification performance of the 2.5V/Ti catalysts, while the Sb modification could improve it by weakening the inhibitory effect of CO. With the introduction of CO, the V⁵⁺ and O_α contents on the surface of 2.5V/Ti catalyst were decreased, which inhibited the NH₃-SCR reaction on the catalyst surface. CO would compete with NH₃ and NO for adsorption on the surface of the 2.5V/Ti catalyst, thus inhibiting the adsorption of NH₃ and the formation of NH₂ intermediates. Meanwhile, because of the presence of CO, surface active bidentate and bridge nitrate production was limited and the reactions between bidentate nitrate and NH₃ as well as NH₃(L) and NO+O₂ were slowed down, which inhibited the NH₃-SCR denitrification performance of the 2.5V/Ti catalysts. The Sb modification significantly increased the O_α content on the catalyst surface and weakened the effect of CO on the V⁵⁺ content on the V-3Sb/Ti catalyst surface through a redox cycle of 2V⁴⁺+Sb⁵⁺$\stackrel{}{\rightleftharpoons }$2V⁵⁺+Sb³⁺. In addition, the Sb modification promoted the formation of SCR reactive species on the catalyst surface and improved the reactivity of NH₃(L) on the surface of the V-3Sb/Ti catalysts in the presence of CO, and thus, the V-3Sb/Ti catalysts exhibited excellent NH₃-SCR performance and better resistance to CO poisoning.

Key words: coal combustion, flue gas, carbon monoxide, SCR, catalyst, Sb modification

摘要：

目前，在燃煤电厂灵活调峰过程中会出现烟气中CO浓度排放过高问题，这会对脱硝系统中钒钛催化剂氨气选择性催化还原（NH₃-SCR）脱硝性能造成影响。本文采用超声浸渍法制备钒钛催化剂及Sb改性钒钛催化剂，研究了CO对钒钛催化剂NH₃-SCR脱硝性能的影响，同时探究了Sb改性对提高钒钛催化剂抗CO中毒机理，通过N₂吸脱附、X射线衍射（XRD）、X射线光电子能谱（XPS）及原位红外漫反射（in-situ DRIFT）等方法对催化剂样品进行了表征分析。结果表明：CO的存在会抑制2.5V/Ti催化剂的NH₃-SCR脱硝活性，Sb改性可以提高催化剂的NH₃-SCR脱硝性能并减弱CO对催化剂脱硝活性的抑制作用。一方面，CO通入后使得2.5V/Ti催化剂表面V⁵⁺和O_α含量减少，抑制了催化剂表面NH₃-SCR反应进行；另一方面，CO会在2.5V/Ti催化剂表面与NH₃和NO产生竞争吸附，抑制催化剂表面NH₃的吸附以及NH₂中间产物的形成，减少表面活性双齿型硝酸盐和桥式硝酸盐的生成并且减缓双齿型硝酸盐和NH₃以及NH₃(L)和NO+O₂的反应，从而抑制了催化剂NH₃-SCR脱硝活性。Sb改性显著增加了催化剂表面O_α的含量，并通过2V⁴⁺+Sb⁵⁺$\stackrel{}{\rightleftharpoons }$2V⁵⁺+Sb³⁺这一氧化还原循环减弱了CO对V-3Sb/Ti催化剂表面V⁵⁺含量的影响。此外，Sb改性还促进了催化剂表面SCR反应活性物种的生成，提高了CO存在时V-3Sb/Ti催化剂表面NH₃（L）的反应性，因此V-3Sb/Ti催化剂表现出优异的NH₃-SCR性能和更好的抗CO中毒特性。

关键词: 煤燃烧, 烟道气, 一氧化碳, 选择性催化还原, 催化剂, 锑改性