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

项目背景(查明问题及其对可持续性的重要性和相关性)用可持续的替代品取代化石燃料的必要性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是多方面的：化石燃料不断被耗尽，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，如农作物损失、冰盖融化和海平面上升。氢燃料就是这样一种替代燃料，由于其循环经济，它是一种可持续的替代燃料，而且只有在燃烧时才会产生水。制氢是催化领域的一个热点问题，而金属催化剂是催化反应的关键，然而这些催化剂往往非常昂贵且稀有，例如铂。这是催化领域常见的困境，两个主要选择是：转向更可持续的金属，或者增加稀有金属的活性。单原子催化剂(SACS)是一项相对较新的技术，已被证明可以极大地提高被吹捧为“下一代”催化剂的催化剂的活性。与传统的负载型金属催化剂相比，催化剂的活性大大提高是由一个主要特征驱动的：提高原子利用率。在多相催化中，只有表面原子才是活性的，表面以下的任何东西都会被浪费。随着金属颗粒尺寸的减小，表面原子的比例增加，原子利用率也随之增加。这大大提高了比活性，并报告了选择性的增加。SACS提供100%的原子利用率，因为每个原子都可用于反应，从而允许最有效和可持续地使用催化剂金属目前SACS的主要问题是它们的稳定性。SACS可以很容易地浸出到溶液中或烧结成大颗粒，这两者都是可持续催化的大问题。与此相关的稳定SACS是我的项目的重点，并在提出的解决方案和方法中进行了讨论。目前最常用的合成SACS的方法是共沉淀法和其他湿化学法，这些方法都是浪费的过程。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载体上，而不产生任何废物。提出的解决方案和方法解决了催化剂的淋滤和烧结问题，催化剂颗粒必须稳定在载体上。在我的项目中，我将通过调整金属有机框架来实现这一点，以赋予这种稳定性。事实证明，缺陷提供的高能中心使催化剂能够更牢固地自我锚定，这意味着烧结和浸出发生的速度要慢得多。通过在合成过程中将缺陷引入MOF，并通过使用Ar等离子体进行合成后修饰，我将创建具有特定控制缺陷的材料(在缺陷类型和数量方面)。为了了解这些有缺陷的MOF，将使用的主要技术是PXRD和TGA。在这些有缺陷的MOF产生后，通过磁控溅射将发生金属催化剂的金属沉积。这些方法将被调整，以创建纳米团簇&lt；2 nm和SACS。然后，这些将被应用于氢气生产，在每次反应后，将主要通过使用x射线光谱分析技术来分析金属原子。结果应该表明，通过引入缺陷，我们正在生产更强大的SAC系统，可以重复使用更多次，这有望朝着最终将SAC引入工业规模的目标迈出一步。

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.