Bond Making and Breaking Processes at Surfaces: Fundamentals of Adsorption and Catalysis

表面的成键和断裂过程：吸附和催化的基础知识

• 批准号: EP/E039782/1
• 负责人: Stephen Jenkins
• 金额: $ 318.66万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FE039782%2F1
• 关键词: Bond; Making; Breaking; Processes; Surfaces

From the platinum-rhodium catalytic converter in your car exhaust system, to the iron catalyst that turns atmospheric nitrogen into fertilizer, highly-reactive metals are key to many of the most important chemical reactions that drive the modern world. Noxious gases like carbon monoxide or nitric oxide, produced in quantity by the internal combustion engine, would naturally revert to less toxic materials in the atmosphere given enough time, but only after causing significant respiratory problems at ground level on our city streets. Similarly, simply mixing nitrogen and hydrogen at high enough pressures would eventually yield the ammonia essential for agriculture, but impossibly slowly. In each case, and in many, many others, the role of the metal catalyst is to speed up and/or re-direct the reaction, preventing environmental pollution or making important high-value chemicals out of uninteresting low-value ones. It is little wonder that the often rare metals involved, from the transition region in the centre of the periodic table, are amongst the most valuable elements in the world, nor that efforts to understand and to optimise their effects are keenly pursued.In many cases, the chemical reactions important in catalysis happen at the surfaces of solid transition metal particles. Passing molecules settle and stick upon the surface (adsorb), move around on the surface (diffuse) and eventually detach from the surface and float away (desorb); in between these basic steps, the molecules may fall apart on the surface (dissociate) or join together to make new molecules (associate). The detailed chemical interactions between the molecules and the metal surface are crucial in determining the relative rates of these five elementary types of process, meaning that each different metal, and indeed each different exposed facet of a metal crystal, may have different catalytic properties. In our work, we make sophisticated measurements of these processes on extremely well-characterised surfaces under highly-controlled conditions. By comparing these with results from our state-of-the-art theoretical calculations, we are able to build up a complete picture of the surface chemistry, and hence to predict better catalysts for future industrial and environmental use. Increasing use of novel alloys and nanostructured surfaces will be a characteristic of our planned work in this direction.The potential for our kind of fundamental surface science to make a significant impact in real-life situations is reflected in the funding we have attracted from industrial sponsors. In recent years, we have been working with Toyota on iridium-gold catalysts for removal of nitric oxide from automobile exhausts, and we have just begun a collaboration with Johnson Matthey looking at the catalytic activation of methane in the same automotive context. Meanwhile, our planned work with BP Alternative Energy is looking towards optimising the production of hydrogen for fuel cell technology, and Shell Research have just committed to work with us towards new routes for ethylene epoxidation.Looking beyond the current applications of surface catalysis, however, we are also focussing a substantial effort in the direction of so-called asymmetric catalysis. The biological molecules found in living organisms are often characterised by the fact that they are chiral, which is to say that they can exist in two inequivalent mirror-image forms. These mirror-image molecules are indistinguishable from each other by most chemical means, but can have radically different behaviour within the body; in many pharmaceutical contexts, therefore, it is vital that drugs be prepared in a pure chiral state. Our research aims to provide an efficient means to achieve this through the use of intrinsically-chiral metal surfaces, which are cut from their parent crystal in such a way as to induce chirally-selective surface chemistry.

从汽车排气系统中的铂铑催化转化器，到将大气中的氮转化为肥料的铁催化剂，高活性金属是推动现代世界发展的许多最重要化学反应的关键。如果有足够的时间，内燃机大量产生的一氧化碳或一氧化氮等有毒气体会在大气中自然地转化为毒性较小的物质，但前提是在我们城市街道的地面造成严重的呼吸系统问题。同样，在足够高的压力下简单地混合氮气和氢气最终会产生农业必需的氨，但速度极其缓慢。在每种情况下，以及在许多其他情况下，金属催化剂的作用是加速和/或重新定向反应，防止环境污染或从无趣的低价值化学品中制造重要的高价值化学品。毫不奇怪，来自元素周期表中心过渡区的稀有金属是世界上最有价值的元素之一，人们也热衷于理解和优化其效果。在许多情况下，催化中重要的化学反应发生在固体过渡金属颗粒的表面。通过的分子沉降并粘附在表面上（吸附），在表面上移动（扩散），最终从表面分离并飘走（解吸）；在这些基本步骤之间，分子可能在表面上分解（解离）或结合在一起形成新分子（缔合）。分子和金属表面之间的详细化学相互作用对于确定这五种基本类型的过程的相对速率至关重要，这意味着每种不同的金属，甚至金属晶体的每个不同的暴露面，可能具有不同的催化特性。在我们的工作中，我们在高度受控的条件下，在特性极其良好的表面上对这些过程进行复杂的测量。通过将这些结果与我们最先进的理论计算结果进行比较，我们能够全面了解表面化学，从而预测未来工业和环境用途的更好催化剂。越来越多地使用新型合金和纳米结构表面将是我们在这个方向上计划工作的一个特点。我们的基础表面科学在现实生活中产生重大影响的潜力反映在我们从工业赞助商那里吸引的资金中。近年来，我们一直与丰田合作开发铱金催化剂，用于去除汽车尾气中的一氧化氮，并且我们刚刚开始与庄信万丰合作，研究在同一汽车环境中甲烷的催化活化。与此同时，我们计划与 BP Alternative Energy 合作，旨在优化燃料电池技术的氢气生产，壳牌研究中心刚刚承诺与我们合作开发乙烯环氧化的新路线。然而，除了表面催化的当前应用之外，我们还将大量精力集中在所谓的不对称催化方向上。生物体中发现的生物分子通常具有手性的特征，也就是说它们可以以两种不等价的镜像形式存在。这些镜像分子通过大多数化学手段都无法区分，但在体内却可能具有截然不同的行为。因此，在许多制药领域，以纯手性状态制备药物至关重要。我们的研究旨在提供一种有效的方法，通过使用本质手性金属表面来实现这一目标，这些金属表面是从其母体晶体上切割下来的，从而诱导手性选择性表面化学。