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

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.

This CDT will deliver impact aligned to the following agendas:

People
A2P will provide over 60 PhD graduates with the skill sets required to deliver innovative sustainable products and processes into the UK chemicals manufacturing industry. A2P will inspire and develop leaders who will:
- understand the needs of industrial end-users;
- embed sustainability across a range of sectors; and
- catalyse the transition to a more productive and resilient UK economy.

Economy
A2P will promote a step change towards a circular economy that embraces resilience and efficiency in terms of atoms and energy. The benefits of adopting more sustainable design principles and smarter production are clear. For example, the global production of active pharmaceutical ingredients (APIs) has been estimated at 65,000-100,000 tonnes per annum. The scale of associated waste is > 10 million tonnes per annum with a disposal cost of more than £15 billion. Consequently, even a modest efficiency increase by applying new, more sustainable chemical processes would deliver substantial economic savings and environmental wins. A2P will seek and deliver systematic gains across all sectors of the chemicals manufacturing industry. Our goals of providing cross-scale training in chemical sciences with economic and life- cycle awareness will drive uptake of sustainable best practice in UK industry, leading to improved economic competitiveness.

Knowledge
This CDT will deliver significant new knowledge in the development of more sustainable processes and products. It will integrate the philosophy of sustainability with catalysis, synthetic methodology, process engineering, and scale-up. Critical concepts such as energy/resource efficiency, life cycle analysis, recycling, and sustainability metrics will become seamlessly joined to what is considered a 'normal' approach to new molecular products. This knowledge and experience will be shared through publications, conferences and other engagement activities. A2P partners will provide efficient routes to market ensuring the efficient translation and transferal of new technologies is realised, ensuring impact is achieved.

Society
The chemistry-using industries manufacture a rich portfolio of products that are critical in maintaining a high quality of life in the UK. A2P will provide highly trained people and new knowledge to develop smarter, better products, whilst increasing the efficiency and sustainability of chemicals manufacture.
To amplify the impacts of our CDT, effective public engagement and technology transfer will become crucially important. As a general comment, 'sustainability' styled research is often regarded in a positive light by society, however, the science that underpins its effective implementation is often poorly appreciated. The University of Nottingham has developed an effective communication portfolio (with dedicated outreach staff) to tackle this issue. In addition to more traditional routes of scientific communication and dissemination, A2P will develop a portfolio of engagement and outreach activities including blogs, webpages, public outreach events, and contribution of material to our award-winning YouTube channel, www.periodicvideos.com.

A2P will build on our successful Sustainable Chemicals and Processes Industry Forum (SCIF), which will provide entry to networks with a wide range of chemical science end-users (spanning multinationals through to speciality SMEs), policy makers and regulators. We will share new scientific developments and best practice with leaders in these areas, to help realise the full impact of our CDT. Annual showcase events will provide a forum where knowledge may be disseminated to partners, we will broaden these events to include participants from thematically linked CDTs from across the UK, we will build on our track record of delivering hi-impact inter-CDT events with complementary centres hosted by the Universities of Bath and Bristol.