Ammonia synthesis revisited: Moving towards the limits of catalysis

Single atom catalysis (SAC) is an exciting, growing field of research which has attracted considerable attention over the last decade. While the field is in its relative infancy, single atom catalysts have been observed to hold a plethora of advantageous characteristics. Aside from an inherent decrease in degree of saturation which can result in higher activity, moving towards smaller catalyst systems results in a shift from the continuous energy bands present in bulk metals, to discrete energy levels in single atoms or small clusters. This change facilitates a range of unique electronic and geometric structures which possess distinct, size-dependent properties relative to the bulk material which have the potential to be exploited for applications such as catalysis, if the relationship between cluster-size and activity can be understood and controlled.



In fact, a number of studies have reported distinct catalytic pathways observed for SACs in comparison to their nanoparticle counterparts, with some displaying enhanced activities and selectivities. This enhancement has been attributed to factors including a higher degree of unsaturation, quantum size effects, significant support-metal interactions and access to different quantum states and configurations. With each of these aspects imparting the possibility of tuneability, SACs provide an opportunity to revisit the optimisation of reactions from a completely new perspective and toolkit.

The Haber-Bosch Process (HBP) is arguably the most famous catalytic reaction, which is estimated to account for 1% of the world's energy usage, because of the harsh operating conditions required. Despite 100 years having passed since the invention of the HBP and substantial research efforts, the ammonia synthesis industry remains dominated by the historic iron catalyst with operating conditions mirroring those described in Haber's Nobel lecture in 1920.

This presents the perfect opportunity to revisit ammonia synthesis from a new lens. Single atom and small cluster catalysts have the potential to give rise to alternative reaction pathways which could allow us to synthesise ammonia at much milder conditions and higher metal utilisation efficiency thus, significantly increasing the sustainability of this essential industrial process.

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.