Creating Highly Stable Single Atom Catalysts on Porous Supports through Magnetron Sputtering

项目背景（识别问题及其重要性和与可持续性的相关性）用可持续替代品取代化石燃料的需求被认为是当今科学家面临的最紧迫的挑战之一。造成这种情况的原因有很多：化石燃料不断枯竭，它们的线性生命周期产生二氧化碳并导致全球变暖，从而产生过多的不利环境影响，如作物损失、冰盖融化和海平面上升。其中一种替代品是氢燃料，它是一种可持续的替代品，因为它具有循环经济，燃烧时只产生水。制氢是催化领域的热门话题，而金属催化剂对该反应至关重要，然而这些催化剂通常非常昂贵和稀有，例如铂。这是催化中常见的困境，有两个主要的选择：转向更可持续的金属，或增加稀有金属的活性。单原子催化剂（SACs）是一种相对较新的技术，已被证明可以极大地提高催化剂的活性，被吹捧为“下一代”催化剂。与传统负载型金属催化剂相比，该催化剂的活性得到了很大的提高，这主要得益于1个特点；增加了原子利用率。在多相催化中，只有表面原子是活跃的，表面以下的原子都被浪费了。随着金属颗粒尺寸的减小，表面原子的比例增加，因此原子的利用率也增加。这大大增加了比活性，也增加了选择性。sac提供了100%的原子利用率，因为每个原子都可用于反应，从而使催化剂金属得到最有效和可持续的利用。目前sac的主要问题是其稳定性。SACs可以很容易地浸出到溶液中或烧结产生大颗粒，这两个都是可持续催化的大问题。在此方面稳定sac是我项目的重点，并在建议的解决方案和方法中进行了讨论。合成SACs最常用的方法是通过共沉淀法和其他湿化学方法，这是一种浪费的过程。一种创新和可持续的SAC生产方法是磁控溅射，这是一种无溶剂的方法，直接将金属原子沉积到支架上，同时不产生废物。为了解决催化剂浸出和烧结的问题，必须将催化剂颗粒稳定在支架上。在我的项目中，我将通过调整金属有机框架来实现这种稳定性。可以确定的是，缺陷提供的高能位点允许催化剂更强地锚定自己，这意味着烧结和浸出的速度要慢得多。通过在mof的合成过程中引入缺陷，并通过氩气等离子体的合成后改性，我将创建具有特定控制缺陷（缺陷类型和数量）的材料。为了了解这些缺陷mof，主要使用了PXRD和TGA技术。在这些缺陷mof形成后，金属催化剂将通过磁控溅射发生金属沉积。该方法将被调整为创建<2nm的纳米团簇和sac。然后这些将被应用于制氢，其中金属原子将在每次反应后进行分析，主要是通过使用x射线光谱学技术。结果应该表明，通过引入缺陷，我们正在生产更健壮的SAC系统，可以被重用更多次，这有望成为在工业规模上引入SAC的最终目标的一步。

Project background (identification of the problem and its importance and relevance to sustainability) The need to replace fossil fuels with sustainable alternatives is understood to be one of the most pressing challenges for scientists today. There are multiple reasons for this: Fossil fuels are constantly being depleted, their linear lifecycle produces carbon dioxide and causes global warming, which produces a plethora of adverse environmental effects such as crop losses, ice cap melting and rising sea levels. One such alternative is hydrogen fuel, which is a sustainable alternative due to its circular economy and only producing water when burned. Hydrogen production is a hot topic in catalysis, and metal catalysts are crucial for this reaction, however these are often very expensive and rare, for example Platinum. This is a common predicament in catalysis, and the 2 main options are: Divert to more sustainable metals, or increase the activity of rare metal. Single atom catalysts (SACs) are a relatively new technology which has been shown to provide hugely increased activity for catalysts, touted as the 'next generation' of catalysts. The greatly improved activity compared to the classical supported metal catalysts is driven by 1 main trait; increased atom utilization. In heterogeneous catalysis only the surface atoms will be active, anything below the surface is wasted. As metal particle size decreases the proportion of atoms at the surface increases, therefore so does the atom utilisation. This yields greatly increased specific activity, as well as reported increases in selectivity. SACs provide 100% atom utilisation, as every atom is available for reaction, allowing the most effective and sustainable use of catalyst metals The main issue with SACs currently is their stability. SACs can quite easily leach into solution or sinter to create large particles, both of which are big problems for sustainable catalysis. Stabilising SACs with respect to this is the focus of my project, and is discussed in Proposed solution and methodology. The most popular method for synthesis of SACs is through co-precipiation and other wet chemistry methods, which is are wasteful processes. An innovative and sustainable method for SAC production is Magnetron sputtering, a solvent free method which directly deposits metal atoms onto a support while producing no waste. Proposed solution and methodology To address the issue of catalyst leaching and sintering, the catalyst particles must be stabilised on the support. In my project I will achieve this by tuning metal-organic frameworks to impart this stability. It is established that the high energy sites provided by defects allow for catalysts to anchor themselves more strongly, meaning that sintering and leaching occurs at a much slower rate. By introducing defects into MOFs during their synthesis and through post synthetic modification using argon plasma, I will create materials with specifically controlled defects (in both their defect type and quantity). To understand these defective MOFs, the main techniques used will be PXRD and TGA. After these defective MOFs have been created, metal deposition of metal catalyst will occur through magnetron sputtering. The methods will be tuned to create nanoclusters <2nm and SACs. These will then be applied to hydrogen production, where the metal atoms will be analysed after each reaction, primarily through the use of x-ray spectroscopy techniques. The results should show that by introducing defects, we are producing more robust SAC systems which can be re-used more times, which would hopefully be a step toward the eventual goal introduction of SACs on industrial scales.