美国威斯康星大学麦迪逊分校（UniversityofWisconsin-Madison）化学与生物工程学教授ManosMavrikakis和马里兰大学（UniversityofMaryland）化学与生物化学教授Bryan Eichhorn近日在《自然—材料学》网络版上发表的论文中描述了一种新型催化剂。它由被一层或两层铂原子包围的钌纳米颗粒组成，是一种高效的室温催化剂，可显著改善关键的氢纯化反应，从而获取更多的氢用于燃料电池的供能。目前，全世界大多数氢的供应来自于化石燃料，这个过程称作重整。科学家相信，燃料电池不久就能通过由可再生能源得到的氢来进行发电。这个过程的重要一步称为PROX反应，它是氢进入燃料电池前，利用催化剂去除其中的CO。CO的存在是燃料电池实际应用的一个主要障碍，因为它毒化了燃料电池反应中昂贵的铂催化剂。
质子交换膜燃料电池能够替代应用于运输工具中的其它电池，它通过利用多孔碳电极进行发电，电极中含有被固体聚合物分开的铂催化剂。氢燃料进入电池的一极，氧进入另一极，铂催化剂促使氢分子中产生质子，这些质子穿过膜与另一极的氧发生反应，结果产生电以及副产品水和热。传统的钌、铂催化剂结合必须达到70℃才能发生PROX反应，但相同的元素以核壳纳米颗粒结构结合后，能够使反应在室温下就发生。催化剂活化反应物以及得到产物的温度越低，节约的能量就越多。产生这种室温反应的原因有两个，首先是催化剂的核壳结构，与单纯的铂催化剂相比，这种特别的结构核成分能够使表面吸收较少的CO，给氧进入并发生反应留下空间。另一个原因是新的反应机理，利用氢原子结合氧分子并生成氢过氧基，这样很容易生成氧原子。氧原子与CO结合生成二氧化碳CO2，这样留下更多的氢分子供给燃料电池。这项突破对于发展燃料电池技术有着重要意义，甚至对催化剂本身的发展也会产生重大影响。（科学网）
生物谷推荐原始出处：
Nature Materials 7, 333 - 338 (2008)
Published online: 16 March 2008 | doi:10.1038/nmat2156
Subject Categories: Catalytic materials | Materials for energy | Nanoscale materials
Ru–Pt core–shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen
Selim Alayoglu1, Anand U. Nilekar2, Manos Mavrikakis2 & Bryan Eichhorn1
Abstract
Most of the world's hydrogen supply is currently obtained by reforming hydrocarbons. 'Reformate' hydrogen contains significant quantities of CO that poison current hydrogen fuel-cell devices. Catalysts are needed to remove CO from hydrogen through selective oxidation. Here, we report first-principles-guided synthesis of a nanoparticle catalyst comprising a Ru core covered with an approximately 1–2-monolayer-thick shell of Pt atoms. The distinct catalytic properties of these well-characterized core–shell nanoparticles were demonstrated for preferential CO oxidation in hydrogen feeds and subsequent hydrogen light-off. For H2 streams containing 1,000 p.p.m. CO, H2 light-off is complete by 30 °C, which is significantly better than for traditional PtRu nano-alloys (85 °C), monometallic mixtures of nanoparticles (93 °C) and pure Pt particles (170 °C). Density functional theory studies suggest that the enhanced catalytic activity for the core–shell nanoparticle originates from a combination of an increased availability of CO-free Pt surface sites on the Ru@Pt nanoparticles and a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.
