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

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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.