工业窑炉烟气氧含量对钒钛系催化剂NH_(3)-SCR脱硝反应的影响

Influence of oxygen content in industrial kiln flue gas on NH_(3)-SCR denitration reaction of vanadium-titanium catalysts

目前,工业窑炉主要采用钒钛系SCR催化剂对烟气中氮氧化物(NO_(x))进行控制,然而工业窑炉部分工序烟气O_(2)含量高,且高O_(2)含量对SCR反应过程的机理影响尚不明确。因此,实验研究了烟气中不同O_(2)含量下钒钛催化剂的脱硝活性,并采用多种表征方法系统分析了O_(2)含量对催化剂物理化学结构的影响;同时结合原位红外技术,进一步揭示了不同O_(2)含量下钒钛催化剂SCR脱硝反应机理。研究表明:在150~400℃的反应温度下,较高O_(2)含量可一定程度提高催化剂的低温脱硝效率,钒负载量增加可使催化剂脱硝活性温度窗口扩展且向低温区移动;催化剂在不同O_(2)含量条件下经过NH_(3)-SCR脱硝反应后,其物理结构变化不明显,反应过程中较高的O_(2)含量可促进催化剂表面酸循环和氧化还原循环,加速SCR脱硝反应;较高O_(2)含量使得SCR反应过程活性中间体NH_(3)(L)和NH^(+)_(4)(B)消耗加快,促进桥型硝酸盐物种的形成,从而提高其SCR脱硝活性。

Currently,industrial kilns mainly use vanadium-titanium-based SCR catalysts to control nitrogen oxides(NO_(x))in flue gas.However,the flue gas generated from industrial kilns contains high oxygen content,and the mechanism in the effect of high O_(2) content on the SCR reaction process over vanadium-titanium catalyst is still unclear.Therefore,the denitration activity of vanadium-titanium catalysts under different O_(2) contents was experimentally studied.The effects of different O_(2) contents on the physical and chemical structure of vanadium titanium catalysts were systematically analyzed by various characterization methods.At the same time,combined with the in-situ infrared technology,the mechanism of SCR denitration reaction of vanadium-titanium catalysts with different O_(2) contents was further revealed.The results show that high O_(2) content can improve the low temperature denitration efficiency of vanadium-titanium catalysts to a certain extent at the reaction temperature of 150-400℃.The increase of the vanadium loading can make the denitration activity temperature window expanding and moving to the low temperature region.After the catalyst undergoes NH_(3)-SCR denitration reaction under different O_(2) content conditions,its physical structure almost unchanged.Higher O_(2) content during the reaction can accelerate the SCR denitration reaction by promoting the acid cycle and redox cycle on the catalyst surface.The active intermediates NH_(3)(L)and NH^(+)_(4)(B)are consumed faster in the SCR reaction process at higher O_(2) content,and high O_(2) content can promote the formation of nitrate species and activate the bridge nitrates,thereby enhancing SCR denitration activity of the vanadium-titanium catalyst.