【作者】 张慧丽；

【导师】 李文翠；

【作者基本信息】 大连理工大学 ， 化学工艺， 2010， 硕士

【摘要】 纳米金催化剂由于优异的低温CO氧化性能在燃料电池、CO防毒面具、CO2激光器及汽车尾气处理器等许多领域具有广泛的应用前景,但是Au催化剂制备的重复性和应用过程中的稳定性问题限制了它的工业应用。研究者发现除了Au活性组分的尺寸和形貌外,载体的种类和微结构对催化剂活性的影响也不容忽视。因此本文工作主要集中研究载体作用。我们选择活性载体CeO2、MnO2以及高稳定性载体SiO2,构建复合氧化物,希望设计出高活性和高稳定性的金催化剂。本文首先考察了还原性载体CeO2和MnO2结构对金催化CO氧化的影响,然后制备了MxNy/SiO2复合氧化物,通过沉积沉淀法制备了Au/MxNy/SiO2催化剂。通过对催化剂结构和催化性能的表征,研究载体对金催化活性的影响。论文第一部分采用初湿浸渍法将CeO2引入到不同微结构的SiO2表面,以制备复合氧化物载体,然后以氯金酸为前体通过沉积沉淀法制备Au/CeO2/SiO2催化剂。通过XRD、氮气物理吸附和TEM等表征了Au/CeO2/SiO2的结构和活性组分的分散状态,通过TPR,HR-TEM,原位DRIFTS等表征揭示了Au/CeO2/SiO2可能的反应机制。多级孔道结构的HMS,保证了Au和CeO2纳米颗粒的均匀分散和相互作用,Au/CeO2/HMS表现了最优的催化活性和较好的稳定性。提高CeO2的含量可得到分散均匀的小尺寸纳米金颗粒,因而催化剂活性提高。Au/CeO2/SiO2的催化行为与Au／CeO2相似。第二部分水热条件下合成了α、β和γ-MnO2,并通过XRD、氮气物理吸附和SEM等表征其结构。采用(NH4)2S2O8为前体,合成了α、β和γ-MnO2,晶型较好的前提下,其横向尺寸的减小有利于CO的转化。α、β和γ-MnO2的催化活性顺序为γ>α>β-MnO2,负载金后,Au-α、γ-MnO2的低温CO氧化能力优于Au-β-MnO2,但Au-β-MnO2完全转化能力强。以KMnO4为前体合成的α-MnO2,负载金之后催化活性明显优于(NH4)2S2O8为前体合成的α-MnO2o第三部分通过浸渍和原位的方式引入MnO2制备Au/MnO2/SiO2催化剂。Au/Mn2O3/SiO2表现了比Au/MnO2/SiO2更优的CO氧化能力。在SBA-15中原位引入棒状MnO2修饰其惰性表面,负载金后Au/MnO2/SBA-15催化活性明显增强。在HMS中原位引入横向尺寸在2-4 nm的枝状MnO2,负载金后,Au/MnO2/HMS催化CO氧化能力也显著增强。综上所述,本文将以还原性氧化物为载体的高活性金催化剂负载至稳定性较好的SiO2表面。Au/MxNy/Si02与Au/SiO2相比催化活性显著提高,与Au/MxNy相比其稳定性也得到增强,因而基本实现了将高催化活性和稳定性相结合的设想。更多还原

【Abstract】 Gold catalysts have potential to be widely used in many fileds such as hydrogen fuel cells, CO gas masks, enclosed CO2 lasers and automobile exhaust processors due to their high activities at low-temperature for CO oxidation. However, the industrial application would be limited for the unsatisfied synthesis repeatability and catalytic stability of active gold catalysts. Besides the morphology and size of the gold nanoparticles, the support is another key factor that influences the catalytic activity. Therefore, the work in this text would concentrate on the effect of support, the active supports of CeO2, MnO2 and silica with high stability were selected to construct composite supports. The gold catalysts with high activity and good stability would be obtained.Firstly, the influences of CeO2 and MnO2 structures on the gold catalysis were evaluated for CO oxidation. Then the composite Au/MxNy/SiO2 catalysts were synthesized with the deposition-precipitation method. The effects of supports were investigated from characterizations of the structures and catalytic abilities of catalysts.In the first part, ceria was introduced with the incipient wetness impreagnation method to modify the silica surface; Au/CeO2/SiO2 catalysts were obtained by a traditional deposition-precipitation method with the hydrochloroauric acid as the precursor. The dispersion of active gold and ceira sites were characterized by XRD, N2 physi-adsorption, TEM et al, and the possible mechanism insights were obtained from TPR, HR-TEM and in situ DRIFTS. HMS with hierachical pores ensured the homogeneous dispersion and the interaction betweem gold and ceria nanoparticles, so it achieved the best catalytic activity and good stability. The silica supports with high ceria content guarantee the small gold nanoparticles with a high dispersion, and the composite catalysts worked much like Au/CeO2.In the second part,α,βandγ-MnO2 were synthesized with a hydrothermal method. A good crystalline and small transverse size was benefical for the CO oxidation from XRD and SEM characterizations. The catalytic activity orders of MnO2 obtained from (NH4)2S2O8was:γ>α>β-MnO2, the order changed after the deposition of gold colloids, at the low temperature range, Au-a-MnO2 and Au-y-MnO2 showed the better activity while Au-β-MnO2 fristly completely converted CO to CO2. The Au/a-MnO2 with the support synthesized from KMnO4 has higher activity than that with (NH4)2S2O8.In the third part, Au/MnO2/SiO2 were synthesized with different methods, MnO2 was introduced by the incipient wetness impregnation or in situ method. Au/Mn2O3/SiO2 had a better ability than Au/MnO2/SiO2 on CO conversion. Nano-rod MnO2 were introduced to the surface of SBA-15 by the in situ method, the composite gold catalysts obtained an improved catalytic activity for CO oxidation. Branchlike nano-MnO2 with the small size were dispersed uniformLy on the HMS with the in situ method, after gold nanoparticles were deposited on MnO2/HMS, the enhanced catalytic activity was obtained on Au/MnO2/HMS.Inconclusion, active gold catalysts with the reductive oxides as the support were deposited on silica. The composite catalyst Au/MxNy/SiO2 showed an improved activity compared to Au/SiO2, and achieved an enhanced stability compared to Au/MxNy.更多还原