【作者】 付名利；

【导师】 叶代启；

【作者基本信息】 华南理工大学 ， 环境工程， 2010， 博士

【摘要】 催化燃烧技术是碳烟去除的一个解决途径,也面临着挑战。其一,柴油车排气中含有一定浓度的SO₂;其二,柴油车排气温度常常低于300-400℃;其三,碳烟的催化燃烧是固-固-气反应,碳烟与催化剂需要良好接触。故催化剂的耐硫中毒性能、低温活性及氧传递能力对碳烟氧化十分重要。论文选用MOx-CeO₂体系（M-Ce-O,M=Fe、Cu、Zn、Co、Ni和Mn）重点是CuO-CeO₂,在程序升温氧化（TPO）反应气氛中引入SO₂,考察SO₂存在下催化剂作用机理。使用XRD、BET、FTIR、H2-TPR、O₂-TPD、NH3-IR以及XPS等表征方法,研究活性影响因素。主要是研究催化剂表面积累硫物种及其对催化剂的表面特性如氧物种、氧化还原对等的作用,以及这种作用对催化活性的影响。主要研究结果与结论如下:（I）对MOx-CeO₂重点是CuO-CeO₂氧化碳烟的活性因子的研究。CeO₂中加入过渡金属氧化物TMO（transient metal oxides）后,由于TM如Cu与Ce之间相互作用形成固溶体,如CeO₂中添加Cu可形成Cu_z²⁺Ce_1-z4+O_2-z²-□z;且一般会伴随着比表面积稍微升高,平均晶粒尺寸减少;固溶体形成意味着更多氧空位（储氧容量OSC）、活性物种如氧物种与氧化还原对Ce4+-O₂--Cu+以及固体表面酸的产生。这些对提高催化剂的活性都有利,本文统称之为活性因子。如共沉淀法（CP）制备的MOx-CeO₂活性顺序为Ni2O3-CeO₂>MnO₂-CeO₂> CuO-CeO₂>Fe2O3-CeO₂>CeO₂>CoO-CeO₂>ZnO-CeO₂,归因于Ni、Mn、Cu及Fe可与Ce作用形成M-Ce-O固溶体,产生更多氧空位和氧物种（可由H2消耗量THC反映）。另如共沉淀法制备的CuO-CeO₂相比于单一的CuO或CeO₂具有更高的活性,也是这些活性因子的作用。再如柠檬酸络合燃烧法（CA）制备的CuO-CeO₂活性排序为Cu0.05Ce0.95>Cu0.2Ce0.8> Cu0.6Ce0.4≈Cu0.8Ce0.2>Cu0.4Ce0.6>CuO,以及Cu0.05Ce0.95-CA活性优于Cu0.05Ce0.95-CP,仍然是归因于上述活性因子的缘故。（II）对SO₂-活性因子-催化剂活性关系的研究。反应气氛中引入SO₂后,其浓度达到一定程度时,会在催化剂表面积累硫物种包括SO₂及其衍生物硫酸盐SO42-、亚硫酸盐SO32-等;可能改变上述包括Ce4+-O₂--Mx+如Ce4+-O₂--Cu+对子以及固体酸在内的活性因子,进而影响活性。如0.03%的SO₂使共沉淀法制备的Fe-Ce-O、Ni-Ce-O和Mn-Ce-O的活性下降,却促进Cu-Ce-O和Co-Ce-O活性,对Zn-Ce-O和CeO₂活性影响不大。另如在0-0.1%浓度范围内,FTIR、BET、NH3-IR以及XPS共同揭示低于0.03%的SO₂在Cu50Ce50（CP）表面生成的SO32-和SO42-累积量低,催化剂Br?nsted酸度提高,净结果是催化活性增强;当SO₂浓度超过0.03%后,SO32-和SO42-累积增加,阻塞了催化剂表面的活性位,活性才降低。再如较低浓度SO₂（0.02%）气氛中Cu_0.05Ce_0.95（CA）活性得到促进,原因是催化剂表面Ce4+增加,超氧O₂-增加,即Ce-O-Cu(Ce⁴⁺-O₂^--Cu⁺)增加。在较高浓度SO₂（0.03%）条件下,Cu_0.05Ce_0.95（CA）晶格氧O₂-和超氧O₂-可能共同转化为O-,后者很可能是硫酸盐。还有,引入0%-0.04%SO₂后,Cu_0.05Ce_0.95-CP/CA活性改变的转折点分别为0.03%与0.02%SO₂,相应FTIR谱图中都在¹385 cm-1处出峰,对应着固溶体表面存在Ce⁴⁺-O₂^--Cu⁺氧化还原对,即催化氧化碳烟的活性位,故对应最佳活性。高浓度（0.04%）SO₂引入后,Cu_0.05Ce_0.95-CA/CP表面都发现硫酸盐在内的硫物种,故活性下降。综上,（i）相比于单一的CeO₂,M’Ox-CeO₂（M’=Ni, Mn,Cu, Fe）如CuO-CeO₂活性更高,主要是因为形成了固溶体,如CuO复合CeO₂生成的Cu_z²⁺Ce_1-z⁴⁺O_2-z^2-□_z;固溶体有利于生成更多氧空位、活性氧物种以及氧化还原对等活性因子。（ii）引入的SO₂通过改变上述活性因子,进而影响活性。一方面可能通过增强催化剂表面固体酸性而促进活性;更重要的是,随着SO₂浓度的升高,在催化剂表面可能积累越来越多包括硫酸盐在内的硫物种,以及减少了表面活性物种如活性氧物种和氧化还原对的含量,抑制了催化剂氧的迁移能力,从而降低了催化剂的活性。总之,催化剂活性受SO₂影响取决于活性因子与硫物种累积量的综合作用。（iii）超氧O₂^-在Cu_0.05Ce_0.95-CP/CA氧化碳烟中的作用是重要的;但用Ce⁴⁺/Ce³⁺比率比活性氧物种O*(O₂^-、O^-和O^2-)能更好的解释催化剂的氧化还原性能。更多还原

【Abstract】 The catalytic combustion technology is a solution for soot abatement and it also presents challenges. Firstly, SO₂ emission from fuel is still a problem for diesel engine; Secondly, the exhaust temperature is always below 300-400℃; Thirdly, the solid-solid-gas reaction type of soot combustion via catalyst, requires a good contact between soot and catalyst. Therefore, the sulfur tolerance, activity at lower temperatures, and oxygen mobility of catalysts play important roles in soot oxidation. As promosing catalysts system, MOx-CeO₂ （M-Ce-O, M=Fe, Cu, Zn, Co, Ni and Mn）, with the emphasis of CuO-CeO₂, were selected to study the mechanism of soot oxidation with the presence of SO₂ in TPO atmosphere. The characterization techniques including XRD, BET, FTIR, H2-TPR, O₂-TPD, NH3-IR and XPS, were applied to explore the activity-affecting factors. For example, the sulfur species deposited on catalyst surface, especially its effect on surface properties including oxygen species, redox couple, thus affecting activity, were investigated. The results and conclusions are as follows:（I）The study on the activity factors for MOx-CeO₂ emphasically for CuO-CeO₂ towards soot oxidation. It was found that the addition of TMO（transient metal oxides） into CeO₂ could cause the formation of solid solution due to the interaction of TMO and ceria, such as Cuz²⁺Ce1-z4+O₂-z2-□z in the case of copper incorporated into ceria; A slight increase of specific surface area（SSA） and decrease of the average crystalline size were observed; The presence of solid solution could lead to the generation of more oxygen vacancies（oxygen storage capacity, OSC）, active species such as oxygen species and Ce4+-O₂--Cu+ redox couple, as well as solid surface acid. The improvement of catalytic activity could benefit from all of those parameters, generally called as activity factors. The activity sequence of MOx-CeO₂ prepared with coprecipitation method（CP） was Ni2O3-CeO₂>MnO₂-CeO₂>CuO-CeO₂>Fe2O3-CeO₂>CeO₂> CoO-CeO₂>ZnO-CeO₂.The addition of Ni, Mn, Cu and Fe could cause the formation of solid solution of M-Ce-O, thus more oxygen vacancies and oxygen species（according to the total hydrogen consumption, THC） are generated. Another example is the superiority at activity for CuO-CeO₂（CP） compared with CuO-only or CeO₂–only catalyst, due to the effect of those above activity factors. Additional examples are CuO-CeO₂（CA） with the activity order of Cu0.05Ce0.95>Cu0.2Ce0.8>Cu0.6Ce0.4≈Cu0.8Ce0.2>Cu0.4Ce0.6>CuO, and the superiroty of the activity of Cu0.05Ce0.95-CA compared with that of Cu0.05Ce0.95-CP. These differences were also resulted from those above activity factors.（II）The study on the correlation of SO₂-activity factors-catalytic activity for soot oxidation. It was found that the concentration of SO₂ in TPO atmosphere increasing to some level could resulted in the deposition of sulfur species on catalyst surface, SO₂, SO42- and SO32-, included; accompanied by the variation of the activity factors, such as Ce⁴⁺-O₂^--M^x+ especially Ce⁴⁺-O₂^--Cu⁺ redox couple, and solid acidity; thus affecting the activity. For example, 0.03%SO₂ could deactivate coprecipitation synthesized Fe-Ce-O, Ni-Ce-O and Mn-Ce-O, however it could enhance the activity of Cu-Ce-O and Co-Ce-O, and no significant effect of SO₂ on Zn-Ce-O or CeO₂ was observed. As another example, FTIR, BET, NH3-IR and XPS reveal that the low amount of SO₄^2-/SO₃^2- on the surface of Cu50Ce50（CP）, with the increase of Br?nsted acidity, result in the accelerated catalytic activity; >0.03%SO₂ could lead to the growth of the amount of SO₄^2-/SO₃^2-, causing the contamination of the active sites and deactivate the catalyst. An additional example was that the activity of Cu0.05Ce0.95（CA） was promoted with the presence of lower concentration of SO₂（0.02%）. This activity enhancement was ascribed to the increase of the amount of surface Ce4+ and superoxide（O₂-）, or due to the enrichment of Ce-O-Cu（Ce4+-O₂--Cu+） from these two kinds of species. In the case of higher concentration of SO₂（0.03%）, lattice oxygen（O₂-） and O₂- transformed to O-, the latter was probably presence in sulfates. Moreover, in the range of 0%-0.04%SO₂, the turning points of activity for Cu0.05Ce0.95-CP and Cu0.05Ce0.95-CA were 0.03% and 0.02%SO₂, respectively. The signals for both two Cu0.05Ce0.95 catalysts at ¹385 cm-1 in FTIR, were assigned as Ce4+-O₂--Cu+ redox couples on the surface of solid, responsible for the active sites of these two catalysts, corresponding to the highest activities. In the case of higher concentration of SO₂（0.04%）, sulfur species including sulfates were found on the surface of Cu0.05Ce0.95-CP and Cu0.05Ce0.95-CA, followed with the inhibition of catalytic activity.As mentioned above, （i）the formation of solid solution in M’Ox-CeO₂（M’=Ni, Mn,Cu, Fe）, such as Cuy²⁺Ce1-y4+O₂-y2-□y in the case of CeO₂ corporated with CuO, caused their higher catalytic activities towards soot oxidation when compared to CeO₂-only. The formation of solid solution could favor the generation of more activity factors including oxygen vacancies, acitive oxygen species, and redox couple. （ii） The above activity factors varied due to the introduction of SO₂, thus affecting the activity. On one hand, the activity could be promoted resulting from the surface solid acid due to the presence of SO₂. The more important is that more sulfur species including sulfates are deposited with the increase of SO₂, followed with the decrease of the amount of surface species such as active oxygen species and redox couple,thus inhibited the oxygen mobility of catalyst and deactivated the catalytic activity. Generally, the effect of SO₂ on the activity of catalysts is determined by the combined action of the so-called active factors and the deposited sulfur species observed in this paper.（iii） In the case of the study of Cu_0.05Ce_0.95-CP/CA, superoxide O₂^- was found to play an important role in soot oxidation, moreover, for the description and interpretation of the redox properties of these two catalysts, the ratio of Ce4+/Ce3+ could be more reliable than active oxygen species O*( O₂^-、O^- and O_<sup>2-).更多还原