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Hydrogen production and purification for fuel cell applications.

机译：用于燃料电池应用的氢气生产和提纯。

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The increased utilization of proton-exchange membrane (PEM) fuel cells as an alternative to internal combustion engines is expected to increase the demand for hydrogen, which is used as the energy source in these systems. Currently, production of hydrogen for fuel cells is primarily achieved via steam reforming, partial oxidation or autothermal reforming of natural gas, or steam reforming of methanol. However, in all of these processes CO is a by-product that must be subsequently removed due to its adverse effects on the Pt-based electrocatalysts of the PEM fuel cell. Our efforts have focused on production of CO-free hydrogen via catalytic decomposition of hydrocarbons and purification of H2 via the preferential oxidation of CO.; The catalytic decomposition of hydrocarbons is an attractive alternative for the production of H2. Previous studies utilizing methane have shown that this approach can indeed produce CO-free hydrogen, with filamentous carbon formed as the by-product and deposited on the catalyst. We have further extended this approach to the decomposition of ethane. In addition to hydrogen and filamentous carbon however, methane is also formed in this case as a by-product. Studies conducted at different temperatures and space velocities suggest that hydrogen is the primary product while methane is formed in a secondary step. Ni/SiO2 catalysts are active for ethane decomposition at temperatures above 500°C. Although the yield of hydrogen increases with temperature, the catalyst deactivation rate also accelerates at higher temperatures.; The preferential oxidation of CO is currently used for the purification of CO-contaminated hydrogen streams due to its efficiency and simplicity. Conventional Pt catalysts used for this reaction have been shown to effectively remove CO, but have limited selectivity (i.e., substantial amounts of H 2 also react with O2). Our work focused on alternative catalytic materials, such as Ru and bimetallic Ru-based catalysts (Pt-Ru, Ru-Sn). We have investigated the effects of various synthetic parameters (namely, supports, pretreatment conditions and precursors) on the performance of supported Ru catalysts. Kinetic results indicate that use of a nitrate precursor, SiO 2 support and a direct H2 treatment results in a highly dispersed catalyst that is active and selective towards CO. The results of extensive characterization studies indicate that a combination of particle size and residual precursor anion poisoning effects are responsible for the observed performance differences.; Bimetallic Ru-Sn catalysts were also examined. Fresh catalyst exhibit lower activity for the preferential oxidation of CO as compared to fresh monometallic Ru. However, the activity of these bimetallic catalysts can be improved significantly by aging under reaction conditions, eventually becoming higher than that of monometallic Ru. By conducting a series of kinetic measurements following treatments with different components of the reacting gas mixture, we were able to deconvolute the effect of the different components and demonstrate that the observed improvement in activity is caused by the interaction of CO and H2O with the catalyst.
机译：质子交换膜（PEM）燃料电池作为内燃机的替代品，其利用率的提高有望增加对氢的需求，氢在这些系统中被用作能源。当前，用于燃料电池的氢的生产主要通过蒸汽重整，天然气的部分氧化或自热重整或甲醇的蒸汽重整来实现。但是，在所有这些过程中，CO是一种副产物，由于其对PEM燃料电池的Pt基电催化剂的不利影响，随后必须除去。我们的工作集中在通过碳氢化合物的催化分解生产无CO的氢气，以及通过CO的优先氧化来提纯H2。烃的催化分解是生产H2的有吸引力的替代方法。先前利用甲烷的研究表明，这种方法确实可以产生无CO的氢气，而丝状碳则作为副产物形成并沉积在催化剂上。我们将这种方法进一步扩展到乙烷的分解。然而，除了氢和丝状碳之外，在这种情况下还形成甲烷作为副产物。在不同温度和空速下进行的研究表明，氢是主要产物，而甲烷是在第二步中形成的。 Ni / SiO2催化剂在高于500°C的温度下对乙烷分解具有活性。尽管氢的产率随温度增加，但催化剂的失活速率在较高温度下也加速。由于CO的优先级和效率，目前优先使用CO的氧化来纯化被CO污染的氢气流。已显示用于该反应的常规Pt催化剂可有效除去CO，但选择性有限（即，大量的H 2也与O 2反应）。我们的工作集中在替代性催化材料上，例如Ru和双金属Ru基催化剂（Pt-Ru，Ru-Sn）。我们已经研究了各种合成参数（即载体，预处理条件和前体）对负载型Ru催化剂性能的影响。动力学结果表明，使用硝酸盐前体，SiO 2载体和直接的H2处理可导致高度分散的催化剂，该催化剂对CO具有活性和选择性。广泛的表征研究结果表明，粒径和残留前体阴离子中毒的组合效果是造成观察到的性能差异的原因。还研究了双金属Ru-Sn催化剂。与新鲜的单金属Ru相比，新鲜的催化剂对优先氧化CO表现出较低的活性。但是，这些双金属催化剂的活性可以通过在反应条件下老化而显着提高，最终变得高于单金属Ru。通过在反应气体混合物的不同成分进行处理之后进行一系列动力学测量，我们能够对不同成分的影响进行反卷积，并证明所观察到的活性提高是由CO和H2O与催化剂的相互作用引起的。

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