【作者】 卢素红；

【导师】 刘源；

【作者基本信息】 天津大学 ， 工业催化， 2012， 博士

【摘要】 富氢气氛中CO优先氧化反应（CO-PROX）作为质子交换膜燃料电池氢源系统中氢气净化的一个重要组成部分,其反应器的“小/微型化”是近年来研究的热点。本文抓住实现富氢气氛中CO-PROX反应器“小/微型化”这一条主线对研究工作进行开展,旨在开发出高性能的新型催化剂,同时有效的缩小CO-PROX反应器的体积。向具有大孔结构的整体型聚苯乙烯（PS）模板中填充氧化铝水溶胶,得到具有大孔结构的α-Al₂O₃（M-α-Al₂O₃）,然后在其大孔壁上添加γ-Al₂O₃涂层,可以提高载体的比表面积,负载活性组分Pt和Ni后用于CO-PROX反应,在1 vol.% CO、1 vol.% O₂、50 vol.% H₂、12.5 vol.% CO₂、15 vol.% H₂O和N2平衡的反应气氛中,体积空速为16,000 h-1的条件下,当反应温度区间为140-180 oC时该催化剂能将CO出口浓度净化到100 ppm以下;该催化剂具有实现CO-PROX反应器小/微型化的潜能。以PS为大孔结构的硬模板,非离子表面活性剂三嵌段共聚物P123为介孔结构的软模板,异丙醇铝为铝源,制备了具有介孔-大孔结构的整体型氧化铝,该材料具有相互连通的大孔结构和蠕虫状的介孔结构;在具有大孔结构的整体型氧化铝的孔壁上组装介孔氧化铝,研究发现通过适当的增加介孔氧化铝的百分含量以及选择合适的焙烧温度可以得到较大的比表面积和所需尺寸的介孔结构。当介孔氧化铝的百分含量为4.4%时,以其为载体负载的Pt-Ni催化剂用于CO-PROX反应具有较好的抗H₂O和CO₂性能。以混酸H₂SO4/HNO3氧化处理后的碳纳米管为载体负载的Pt-Ni催化剂用于CO-PROX反应,在1 vol.% CO、1 vol.% O₂、50 vol.% H₂和N2平衡的反应气氛中,该催化剂具有较高的催化活性和选择性,反应气氛中12.5 vol.% CO₂的加入,对CO的转化率具有轻微的负面影响。而15 vol.% H₂O的加入使CO的转化率在100-120 oC降低,可能是由于水通过毛细管作用凝聚在碳纳米管的微孔中;当反应温度升高时,水的加入对CO的转化具有促进作用。向PS模板中填充碳纳米管-氧化铝水溶胶,制备得到了碳纳米管-氧化铝复合的具有介孔-大孔结构的整体型材料。该整体型复合材料具有相互连通的大孔结构和可调的介孔,并且碳纳米管可以均匀分散在氧化铝基体中。研究发现加入适量的CNTs以及在合适的焙烧温度条件下可以有效的提高复合材料的抗压强度以及导热系数,其中整体型复合材料5 wt.% CNT-Al₂O₃-1300-M具有很好的抗压强度和导热系数。以其为载体负载的Pt-Ni催化剂用于CO-PROX反应,在1 vol.% CO、1 vol.% O₂、50 vol.% H₂、12.5 vol.% CO₂、15 vol.% H₂O和N2平衡的反应气氛中,体积空速为10,400 h-1的条件下,在120-180 oC的温度区间内可以将CO的出口浓度降到100 ppm以下,并且该催化剂具有较好的稳定性。更多还原

【Abstract】 The preferential oxidation of CO （CO-PROX） is a requisite step of hydrogen generator process for proton exchange membrane fuel cells. Recently, the miniaturization of the CO-PROX reactor has been the focus of widespread research. This work is to develop a new catalyst with high catalytic performance for CO-PROX, as well as to meet the requirements of the miniaturization.The macroporous monolithicα-Al₂O₃ （referred to M-α-Al₂O₃） was prepared by imbibing macroporous polystyrene foams with alumina hydrosols. Addingγ-Al₂O₃ to the macroporous walls could increase the specific surface area of M-α-Al₂O₃. Using M-γ/α-Al₂O₃ as supports loaded Pt-Ni catalyst for the CO-PROX reaction. This catalyst could purify the exit concentration of CO to less than 100 ppm in the temperature range of 140-180oC in 1 vol. % CO, 1 vol. % O₂, 50 vol. % H₂, 12.5 vol.% CO₂, 15 vol.% H₂O and N2 gases with a volume space velocity of 16,000 h-1. The results show that preparing catalysts to macroporous monolithic structure is a promising way for the miniaturization of CO removing reator.The meso-macroporous monolithic alumina was fabricated via using aluminum iso-propoxide as a alumina precursor, nonionic surfactant triblock copolymer P123 as a soft template for the meso-structure and PS as a hard template for macro-structure. The prepared samples had interconnected macropores and wormhole-like mesopores. Mesoporous alumina could assemble on the macroporous walls of M-α-Al₂O₃. The specific surface area and meso-structure of sample were affected by the loading amount of mesoporous alumina. The sample with 4.4% amount of mesoporous alumina was used as support to load Pt-Ni catalyst for the CO-PROX reaction. The experimental results indicated that the prepared catalyst was well tolerant to CO₂ and H₂O.Carbon nanotubes oxidized with H₂SO4/HNO3 solution supported Pt-Ni catalysts were prepared and used for CO-PROX. The results of catalytic preformance tests showed that the prepared catalysts were very active and highly selective at low temperature in 1 vol. % CO, 1 vol. % O₂, 50 vol. % H₂ and N2 gases. Adding 12.5 vol. % of CO₂ into the feed gases had slight negative influence on CO conversion. Adding 15 vol. % of H₂O led to a little decrease of CO conversion at the temperature range of 100 to 120 oC, which was proposed to be caused by capillary wetting of water in the micro-pores of carbon nanotubes. As the reaction temperature was higher, adding water could improve CO conversion.A series of carbon nanotube （CNT）-alumina composite monoliths with meso-macroporous structures were successfully synthesized by imbibing macroporous monolithic polystyrene foams with carbon nanotube-alumina hydrosols. These composite monoliths possessed interconnected spherical macropores and adjustable mesopores of several nanometers. CNTs were uniformly dispersed throughout the alumina matrix. The mechanical strength and thermal conductivity of composite monoliths can be improved with adding appropriate amounts of CNTs and with suitable calcination temperature. The sample of 5 wt.% CNT-Al₂O₃-1300-M had good mechnical strenghth and high thermal conductivity. The Pt-Ni/CNT-Al₂O₃ monoliths exhibited high activity and selectivity. The residual concentration of CO was purified to less than 100 ppm in the temperature range of 120-180oC in 1 vol. % CO, 1 vol. % O₂, 50 vol. % H₂, 12.5 vol.% CO₂, 15 vol.% H₂O and N2 gases with a volume space velocity of 10,400 h-1. This catalyst exhibited good stability.更多还原