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选择性催化还原(SCR)是目前去除氮氧化物最有效的方法之一.V_2O_5/TiO_2催化剂被广泛应用于氨法选择性还原氮氧化物(NH_3-SCR)反应,但该催化剂存在工作温度高(300–400℃)及SO_2氧化率高引起设备腐蚀和管路堵塞等问题,开发低温SCR催化剂具有重要意义.过渡金属氧化物(如Fe_2O_3,MnO_x和CuO等)催化剂用于低温SCR先后见诸文献报道,但这些催化剂在SO_2和H_2O存在下易失活.近年来柱撑黏土(PILC)引起科学家广泛关注,Yang等首次将V_2O_5/TiO_2-PILC催化剂应用于NH_3-SCR反应,发现其催化活性高于传统V_2O_5/TiO_2催化剂.柱撑黏土基催化剂在NH_3-SCR反应中也显示出良好抗硫性能,但V_2O_5/TiO_2-PILC催化剂的抗硫机理至今尚未见深入研究.因此我们制备了一系列V_2O_5/TiO_2-PILC催化剂,采用原位漫反射红外等方法详细研究了其抗硫性能较好的原因.首先采用离子交换法制备出TiO_2-PILC载体,之后采用浸渍法制备了不同钒含量(质量分数x/%=0,3,4,5)的xV_2O_5/TiO_2-PILC催化剂.同时,制备了传统V_2O_5/TiO_2和V2O5-MoO_3/TiO_2催化剂作为对比.活性评价结果显示,4V/TiO_2-PILC催化剂具有最高的催化活性,其催化性能与传统钒钛催化剂相当.在160℃时,NO转化率可达80%以上.同时,4V/TiO_2-PILC催化剂还具有较宽的反应温度窗口,在260–500℃范围内,NO转化率保持在90%以上.向反应体系中加入0.05%SO_2和10%H_2O后,在低温(160℃以下)时所有催化剂的反应活性都有一定提高,可能是由于SO_2的加入提高了催化剂的表面酸性.继续升高温度,4V/TiO_2和4V6Mo/TiO_2催化剂活性均明显下降,而4V/TiO_2-PILC催化剂的活性则未出现明显下降.原位漫反射红外光谱结果显示,SO_2在三种催化剂表面的吸附以表面硫酸盐或亚硫酸盐物种以及离子态SO_4~(2–)物种形式存在,而在4V/TiO_2-PILC催化剂表面离子态SO_4~(2–)物种的量最少.X射线光电子能谱及O_2程序升温脱附结果显示,在4V/TiO_2-PILC催化剂上,表面吸附氧(Oads)的量最少.综合上述分析可以得出,在SO_2气氛下,离子态SO_4~(2–)物种在SCR催化剂表面的累积可能是导致其失活的主要原因,而离子态SO_4~(2–)物种的形成可能与催化剂表面吸附氧的量有关.
Selective catalytic reduction (SCR) is one of the most effective methods to remove nitrogen oxides currently.V_2O_5 / TiO_2 catalysts are widely used in the selective reduction of nitrogen oxides (NH_3-SCR) by ammonia method, but the catalysts have high operating temperature (300-400 ℃) and high SO 2 oxidation rate lead to equipment corrosion and pipeline blockage, the development of low temperature SCR catalyst is of great significance.Transition metal oxides (such as Fe_2O_3, MnO_x and CuO) However, these catalysts are easily deactivated in the presence of SO 2 and H 2 O. In recent years, Pillars Clay (PILC) has drawn the attention of scientists. For the first time, Yang et al. Applied the V 2 O 5 / TiO 2 -PLC catalyst to NH 3-SCR reaction and found its catalytic activity Pillared clay-based catalysts also showed good sulfur resistance in NH 3-SCR reaction, but the mechanism of sulfur resistance of V 2 O 5 / TiO 2 -PLC catalysts has not been further studied so far, we have prepared a series of V_2O_5 / TiO_2-PILC catalyst, in-situ diffuse reflectance infrared method was used to study the reason of its good sulfur resistance.Firstly, TiO_2-PILC carrier was prepared by ion exchange method, The XV_2O_5 / TiO_2-PILC catalysts with different vanadium content (mass fraction x /% = 0, 3, 4, 5) were prepared by the stain method and the conventional V 2 O 5 / TiO 2 and V 2 O 5 -MoO 3 / TiO 2 catalysts were prepared for comparison. The results show that the 4V / TiO_2-PILC catalyst has the highest catalytic activity and the catalytic performance is comparable to that of the conventional vanadium-titanium catalyst, and the NO conversion reaches more than 80% at 160 ℃ .At the same time, the 4V / The wide reaction temperature window maintains the NO conversion above 90% in the range of 260-500 ° C. The reactivity of all catalysts at low temperatures (up to 160 ° C) with 0.05% SO 2 and 10% H 2 O added to the reaction system , Which may be attributed to the increase of the surface acidity of the catalyst due to the addition of SO 2. The activity of 4V / TiO 2 and 4V6Mo / TiO 2 catalysts decreased obviously while the temperature continued to increase, while the activity of 4V / TiO 2 -PLC catalyst did not decrease significantly The results of in-situ diffuse reflectance infrared spectroscopy showed that the adsorption of SO 2 on the three catalyst surfaces was in the form of surface sulfate or sulfite species and SO 4 2- species in the ionic state, while that on the surface of 4V / TiO 2 -PLC catalyst State SO_4 ~ (2-) the least amount of species. X-ray The results of electron spectroscopy and O 2 temperature-programmed desorption showed that the amount of Oads on the surface of 4V / TiO_2-PILC catalyst was the least. Based on the above analysis, it can be concluded that in SO_2 atmosphere, the ionic state of SO_4 ~ (2- The accumulation of species on the surface of SCR catalyst may be the main reason for its deactivation, while the formation of ionic SO 4 2- species may be related to the amount of oxygen adsorbed on the catalyst surface.