Metal Nanoclusters as Heterogeneous Catalysts in Flow Reactors

Metal nanoclusters (MNCs) are metal atom clusters with diameters smaller than 2.0 nm, and can be composed of a single or multiple metals. MNCs show promise as heterogeneous catalysts, where the clusters are deposited on a support or encapsulated. These catalysts achieve the high surface area of traditional homogeneous catalysts exhibiting high activity and selectivity, whilst retaining the stability and separation ease of heterogeneous catalysts. Such characteristics can enable performance that is not achievable using nanoparticle or single atom catalysts. MNC catalysts also drastically reduce the amount of metal required for catalysis which is beneficial for rare or expensive metals and highly desirable from a sustainability perspective.

To date, MNCs have generally been synthesised using wet chemistry methods which require multiple steps, produce waste and are not scalable, preventing commercial application. One preparation technique that can overcome these issues is magnetron sputtering. This physical process can disperse planar metal clusters directly onto supports in a single step, with a high level of control over metal loading and cluster size. Unlike wet chemistry methods, the process does not produce any chemical waste which is crucial as it becomes more important to reduce the impact of chemical research on the environment. The use of magnetron sputtering will also enable MNC heterogeneous catalysts to be generated at a scale and throughput that does not limit their research.

In parallel to this, heterogeneous catalysis in flow is a growing field and presents huge potential to improve existing chemical processes as well as develop new and more sustainable chemistry. Commonly, packed bed reactors are used, however these can have limitations with respect to mixing, heat transfer and control over the flow of the reaction mixture. As a result, many novel reactor systems have been developed such as 3D-printed inserts and vortex devices.

Proposed solution and methodology

In this project, the two emerging sustainable technologies will be bridged together; MNCs will be fabricated by magnetron sputtering, and then used as heterogeneous catalysts in liquid flow. To the best of our knowledge, MNC catalysts have not yet been demonstrated in liquid flow, and it is not known which flow reactor approach would be best to harness their unique properties. This is a challenging question because specifics of MNC fabrication will be different for different flow reactor technologies. This project is set to establish MNC catalyst behaviour and performance in flow which is critically important for industrial challenges related to the sustainable use of transition metals for heterogeneous catalysis of flow processes.

To achieve this step change a multidisciplinary approach is required. Heterogeneous MNC catalyst systems will be characterised through imaging and spectroscopy to understand their behaviour. Reaction outputs including product conversion, product purity and reaction rate will be analysed to understand catalyst performance. Carrying out the reactions in a variety of flow reactors will help to understand how different support types and reaction conditions impact this behaviour and performance. Initially, Palladium MNCs will be investigated with hydrogenation as a model reaction.

By the end of the project we aim to have developed a new generation of high performing and sustainable heterogeneous catalysts for liquid flow with potential for application to industrially important reactions.

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.