硫掺杂铈基催化剂的制备及其脱硝性能的研究

发布时间：2018-03-13 22:32

本文选题：NH_3选择性催化还原　切入点：铈基催化剂　出处：《南京理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：氮氧化物(NO_x)是大气污染的主要污染源之一。铈基催化剂在选择性催化还原NO_x展现了良好的性能。然而在水汽和SO_2存在的情况下其脱硝活性严重地受到了抑制。本文采用沉淀法制备PS-NCLS、Cu-Ce(S)等铈基催化剂。分别通过SO_2预处理和加入硫酸盐前驱体两种方法对催化剂进行硫元素掺杂改性以提高其抗水抗硫性能。采用X射线衍射(XRD)、透射电镜(TEM)、X射线光电子能谱(XPS)、程序升温脱附(TPD)、傅里叶变换红外(FTIR)、原位漫反射红外(in situ DRIFTS)、热重(TG)等分析测试方法对催化剂的结构和形貌、反应机理和改性的作用等进行了研究。在固定床反应器测试了催化剂的脱硝活性及抗水抗硫性能。对于PS-NCLS催化剂,La~(3+)掺杂进CeO_2萤石晶格中导致了晶胞的膨胀,产生了更多的晶格缺陷并提升了晶格氧的流动性。Ni~(2+)在催化剂表面富集,形成了新的Lewis酸性位。硫酸化处理增加了催化剂中Ce~(3+)和化学吸附氧的比例,并提升了晶格氧的流动性。通过硫酸化处理,催化剂保留了多数Lewis酸性位并生成了新的Bronsted酸性位。提出了缩核模型来解释催化剂的硫酸化过程。此外,原位漫反射红外实验证实了硫酸化处理后催化剂上NH_3-SCR反应主要遵循L-H机理。硫酸化处理后的PS-NCLS催化剂在水汽和SO_2共存条件下保留了良好的NO吸附性,并增加了 NH_3的吸附性。这些结果阐述了Ni和La的引入以及硫酸化处理对催化剂的脱硝活性和抗水抗硫性能的提升具有重要的作用。对于Cu-Ce(S)催化剂,随着Cu掺杂量的增加,Cu-Ce固溶体中掺杂的Cu~(2+)趋于饱和,CuO相开始出现并分散在催化剂表面。较低的Cu掺杂量具有较高的Ce~(3+)比例,导致了催化剂较强的Lewis酸性。化学吸附氧的比例随着Cu掺杂量的增加而增加。Cu-Ce(S)催化剂中的SO_4~(2-)增强了催化剂的Bronsted酸性。在水汽和SO_2共存情况下,催化剂表面出现了亚硫酸铵盐和硫酸铵盐的沉积,而掺杂的Cu抑制了铵盐的沉积现象。3%Cu-Ce(S)催化剂比CeO_2催化剂具有更宽的温度窗口、更好的的中低温脱硝活性和抗水抗硫性能。
[Abstract]:No _ x) is one of the main pollution sources of air pollution. Cerium based catalyst shows good performance in selective catalytic reduction of NO_x. However, the denitrification activity is severely inhibited in the presence of water vapor and SO_2. Cerium-based catalysts such as PS-NCLS- Cu-CeS-) were prepared by precipitation method. The catalysts were modified by SO_2 pretreatment and sulphate precursor respectively in order to improve their water resistance and sulfur resistance. X-ray diffraction (XRD) and permeation were used to improve the water resistance and sulfur resistance of the catalysts. The structure and morphology of the catalyst were studied by means of X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), Fourier transform infrared spectroscopy (FTIR), in situ diffuse reflectance infrared spectroscopy (DIR) in situ, thermogravimetry (TG), etc. The mechanism of the reaction and the effect of modification were studied. The denitrification activity and water resistance to sulfur of the catalyst were tested in a fixed bed reactor. For the PS-NCLS catalyst, Lajian3) doping into the CeO_2 fluorite lattice resulted in the expansion of the unit cell. More lattice defects were produced and the mobility of lattice oxygen was enhanced. Ni2) was enriched on the surface of the catalyst to form a new acidic site of Lewis. Sulfation treatment increased the ratio of Ce~(3) and chemisorbed oxygen in the catalyst. The mobility of lattice oxygen was enhanced. Through sulfation treatment, the catalyst retained most of the acidic sites of Lewis and formed a new acidic site of Bronsted. A shrinking nucleation model was proposed to explain the sulfation process of the catalyst. In situ diffuse reflectance infrared (DIR) experiments confirmed that the NH_3-SCR reaction on the sulfated catalyst mainly followed the L-H mechanism. The sulfated PS-NCLS catalyst retained good no adsorption under the condition of coexistence of water vapor and SO_2. The results show that the introduction of Ni and La and the sulfation treatment play an important role in the denitrification activity of the catalyst and the improvement of water resistance to sulfur. With the increase of Cu doping amount, the Cu~(2 doped in Cu-Ce solid solution tends to appear in saturated CuO phase and disperse on the surface of the catalyst. The lower Cu doping content has a higher Ce~(3) ratio. The ratio of chemisorbed oxygen to oxygen increased with the increase of Cu doping content. The SO4C _ 2) enhanced the Bronsted acidity of the catalyst. Under the condition of the coexistence of water vapor and SO_2, the acidity of the catalyst was enhanced. The deposition of ammonium sulfite and ammonium sulfate appeared on the surface of the catalyst, while Cu doping inhibited the deposition of ammonium salt. 3Cu-CeS) catalyst had wider temperature window, better denitrification activity and water resistance to sulfur than CeO_2 catalyst.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;X701

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