【作者】 陈鸿庆；

【导师】 彭峰；

【作者基本信息】 华南理工大学 ， 工业催化， 2010， 博士

【摘要】 乙醇自热重整（ATRE）制氢效率高、选择性好,在便携式氢源方面有着广泛的应用前景。但自热反应高温、复杂,必须开发高效实用的催化剂及反应器。本文优化筛选了乙醇自热制氢催化剂材料。在最佳组分催化剂Ir/La₂O₃上对Ir-La相互作用进行了研究,发现了Ir的原位分散效应,指出了进一步提高催化剂性能的思路和方法。在此基础上,本文合成了结构型Ir/La₂O₃催化剂并在微型反应器中进行了ATRE制氢研究。采用Fluent模拟和实验相结合的方法对微型反应器内原料优化分布进行了研究,以进一步提高制氢性能。采用自燃烧的方法制备了钙钛矿型的LaMnO₃,LaFeO₃,LaCoO₃和LaNiO₃氧化物并用于ATRE制氢反应。还原LaNiO₃获得的负载在La₂O₃上的高度分散的Ni具有最高的ATRE反应性能。它有助于促进乙醇脱氢,乙醇、乙醛分解、甲烷重整和水汽变换反应。通过对还原LaNiO₃和浸渍方法获得的Ni/La₂O₃的对比研究表明前者能够提高Ni的分散,从而提高了反应的活性和稳定性。鉴于Ni催化剂具有较差的稳定性,本文以贵金属（Ir、Ru、Rh和Pd）为活性组分,以氧化物（γ-Al₂O₃、CeO₂、ZrO₂和La₂O₃）为载体制备了贵金属型催化剂并进行了乙醇自热/氧化重整制氢研究。氧化镧具有相当高的ATRE反应活性,是ATRE催化剂的良好功能载体。Ir/La₂O₃能够避免甲烷的形成,具有良好的ATRE选择性和稳定性,值得作为目标催化剂并用于进一步的研究。以氧化蒸气重整乙醇为模型体系,对Ir-La相互作用进行了研究。在反应过程中,La₂O₃能够转变形成六方的La₂O₂CO₃,还原过的Ir能够与La₂O₂CO₃反应形成Ir掺杂的La₂O₂CO₃。反应过程中这种复合物动态的形成和分解,释放出高度活性的Ir纳米颗粒,防止了Ir/La₂O₃催化剂的烧结,并在一定的温度范围内推动Ir的自发分散。采用超声辅助的浸渍方法可以显著的提高Ir的初始分散度,增强Ir的原位分散效应。Ir负载量为9 wt%的Ir/La₂O₃催化剂在650℃经过长达100 h的OSRE反应没有显示出任何失活现象,用过催化剂中Ir的粒径只有3.2 nm。采用泡沫陶瓷（Al₂O₃、SiC和ZrO₂）制备了结构型Ir/La₂O₃催化剂并进行了ATRE反应制氢研究。泡沫材料对反应性能有重要影响。在ZrO₂泡沫上,Ir/La₂O₃催化剂具有最好的ATRE制氢性能。催化层中La的含量对Ir初始分散度具有显著影响。对用过催化剂的Ir粒径研究表明负载在ZrO₂上的Ir/La₂O₃催化剂仍然保留了良好的原位分散效应。对微型反应器的研究表明ATRE对原料的响应时间为90 s,1 mol乙醇可以获得3.1 mol的氢气,微型反应器也具有良好的启动、反应稳定性能。采用实验与Fluent模拟相结合的方法对微型反应器内原料的分布以及ATRE性能进行了系统研究。不采用分布器则原料集中于催化剂的中心区域,降低了催化剂利用效率以及反应器性能。模拟结果表明微反内使用半径为7 mm的半球分布器最为合理。实验结果表明半球形分布器具有最好的原料分布效果,微反的ATRE反应性能也最好,观测到的催化剂底表面的最大温差只有21℃。在空速1.6×105 1/h下,原料的转化率达到91 %,相应的氢气选择性为74.1 %,平均从1 mol乙醇中可以获得3.3 mol氢气,产品气中氢气的流量达到0.58m3/h,可以供大约1100 W的燃料电池使用。这些结果对于设计高效微型自热重整制氢反应器具有很高的指导意义。更多还原

【Abstract】 Autothermal Reforming （ATRE） process has attracted much attention as it offers advantages on efficiency for hydrogen production and less dependence on additional power sources. However, effective catalyst and reactor should be required as the ATRE reaction is complex, and requires high temperature （500⁸00℃）. The materials for synthesizing the ATRE catalyst were investigated carefully, the result Ir/La₂O₃ was high active and stable for ATRE reaction for hydrogen and Ir-La interaction during the reaction was studied systemically. An in situ dispersion effect of Ir on La₂O₂CO₃ support was observed, and an upgrade Ir/La₂O₃ base on this effect was obtained. Subsequently, an active and selective Ir-La structured catalyst was synthesized. The reactants distribution on the catalyst surface and its influences on the ATRE performances were investigated and optimized.LaMnO₃, LaFeO₃, LaCoO₃ and LaNiO₃ perovskite oxides were prepared using combustion method for the autothermal reforming of ethanol （ATRE）. The perovskite-type oxides can catalyze the ATRE reaction with a moderate activity. Well dispersed Ni particles supported on lanthanum oxide species were obtained by reducing the LaNiO₃ sample. It favors the dehydrogenation, decomposition of ethanol/acetaldehyde, methane reforming and water gas shift reactions, thus leads to good activity and H2 selectivity in ATRE reaction. A comparison between LaNiO₃ derived and impregnated Ni/La₂O₃ shows that the LaNiO₃ derived sample favored the dispersion of Ni, which increased the activity and the resistance to coke deposition.Hydrogen was produced over noble metal （Ir, Ru, Rh, Pd） catalysts supported on various oxides, includingγ-Al₂O₃, CeO₂, ZrO₂ and La₂O₃, via the autothermal reforming reaction of ethanol （ATRE） and oxidation reforming reaction of ethanol （OSRE）. It was discovered that lanthana alone have considerable activity for the ATRE reaction, which can be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La₂O₃ can prevent the formation of methane. ATRE reaction can be carried out over La₂O₃-supported catalysts （Ir/La₂O₃） with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limitation under autothermal condition. The results presented in this paper indicate that Ir/La₂O₃ can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.La₂O₃ supported Ir catalyst was prepared by wetness impregnation method for the oxidative steam reforming of ethanol （OSRE）. La₂O₃ would transform into hexagonal La₂O₂CO₃ during OSRE, which suppress coking effectively. Reduced Ir metal can interplay with La₂O₂CO₃ to form Ir doped La₂O₂CO₃. It dynamically forms and decomposes to release active Ir nanoparticles, thereby prevent the catalyst from sintering and afford high dispersion of Ir/La₂O₃ catalysts at elevated temperatures. By introducing ultrasonic during the preparation of catalyst, the surface Ir concentration was significantly improved, while the in situ dispersion effect inhibited Ir from sintering. The Ir/La₂O₃ catalyst by the ultrasonic assistant impregnation method is highly active and stable for the OSRE reaction, on which the Ir crystallite size was maintained at 3.2 nm after 100 h on stream at 650℃and metal loading high up to 9 wt%.An ethanol autothermal reforming micro-reformer was constructed to produce hydrogen for polymer electrolyte membrane fuel cells （PEMFCs）, in which an Ir/La₂O₃ catalyst supported on ceramic foams was employed. To optimize the performance of micro-reformer, the effect of ceramic foam materials, including Al₂O₃, SiC and ZrO₂ foams, on the catalytic property was investigated in details from the aspects of activity, selectivity and stability. It was found that the ZrO₂ foam was the most suitable material to support the Ir/La₂O₃ catalyst. The La content in the catalyst layer influences the Ir dispersion greatly. The in situ dispersion effect of Ir on La oxide support worked well. The in situ dispersion effect improved the ethanol reforming activity, selectivity and stability significantly. Based on this, an Ir-La/ZrO₂ structured catalyst was synthesized to catalyze the ATRE reaction for hydrogen production in the micro-reformer. The outlet temperature distribution, product gas composition and reaction stability were investigated systematically. A reagent corresponding time of ⁹0 s was obtained in this micro-reformer. It produced 3.1 mol H2 per mol ethanol, and showed nice stability for reaction start-up and stable reaction. The distribution of reagents on the surface of catalyst and its influences on the ATRE performances were investigated by the Fluent simulation and the experiment. The reagents passed though the center of the catalyst without any obvious diffusion since the distributor was absent in the reactor. According to simulating results, by fixing a distributor in the entrance of the reactor, the uneven distribution of reagents on the surface of the catalyst was depressed. Hemisphere with a diameter of 14mm as distributor showed the most promising distribution performance. The experiment results showed that the conversion of ethanol and selectivity to hydrogen were improved greatly by this hemisphere distributor. The largest difference in temperature obtained on the outlet of the catalyst was only 21oC. At lower space velocity （GHSV=8.4×10⁴ 1/h）, the distribution performance of hemisphere （14mm） observed by experiment data fit well with that from fluent simulation. Improving the GHSV further, the agreement between the two was unsatisfactory probably due to the error during the fabrication of the reactor. However, the micro-reformer with hemisphere （14mm） distributor can convert 91% ethanol with a hydrogen selectivity of 74.1% at GHSV=1.6×105 1/h under ATRE reaction condition. It produced 3.3 mol H₂ per mol ethanol, with a hydrogen flow rate of ⁰.58m³/h, which can feed fuel cells to produce power at 1100 W level. These results are helpful for the rational design and fabrication of micro-reformers for PEMFCs.更多还原