Catalysis for the Climate Change Challenge: Iron-based alloys as catalysts for CO2 Hydrogenation

“Climate change is a global challenge that does not respect national borders. It is an issue that requires solutions that need to be coordinated at the international level to help developing countries move toward a low-carbon economy.” UN Sustainable Development Goal 13 

The UN Climate Panel (IPCC) calls for the elimination and reversal of CO₂ emissions to the atmosphere as a matter of urgency to avoid potentially “catastrophic climate change”. One of the main barriers to this, however, is the large amount of readily available energy in the form of fossil fuels, which is currently hard to compete with using alternative or renewable sources, particularly on the African continent.  

Closing the carbon cycle and CO₂ hydrogenation 

Carbon dioxide capture, utilisation and storage are some of the options cited by the IPCC in order to achieve “the deep emissions reductions required in energy-intensive industries to limit global warming to 1.5°C” (IPCC, 2018).  

To tackle this challenge, researchers Dr Mohamed Fadlalla and Chris Mullins from the University of Cape Town’s Centre of Catalysis are investigating CO₂ hydrogenation reactions in the simultaneous sequestration of CO₂ and provision of readily available fuel. Their project is made possible via the GCRF START and access to the UK’s national synchrotron light source, Diamond. 

“We are looking to close the cycle of CO₂ using hydrogen from renewable energies to produce fuels that could be used in transportation or energy generation. The latter would also produce CO₂ which we would then convert to fuels,” explains Chris Mullins, a Master’s student working on the project. “These fuels, often referred to as ‘e-fuels’ or ‘power fuels’, may play an important role in future de-fossilisation, particularly in the aviation industry where high density fuels are required.” 

Dr Fadlalla and Chris Mullins are exploring the direct and indirect hydrogenation routes of CO₂. The latter makes use of a synthesis gas (CO + H₂) which can be derived via a reverse water gas shift reaction, which is then converted using the Fischer-Tropsch reaction (a series of chemical reactions that involve the conversion of hydrogen and carbon monoxide into liquid hydrocarbons by using a catalyst). 

Investigating iron-based bimetallic catalysts 

The bottleneck in making the hydrocarbon fuels process viable, however, is the choice of catalysts to facilitate this process. The current iron catalysts are inefficient and prone to forming undesirable by-products.  

Recently, it has been found that a combination of iron with other metals greatly enhances their effectiveness as catalysts for CO₂ hydrogenation, although the mechanisms which lead to this enhanced performance remain unknown^[1].  

The aim of the scientists is to identify the parameters of iron-based bimetallic catalysts which lead to enhanced CO₂ hydrogenation performance, as Dr Fadlalla explains,   

“Intelligent design of catalytic material for the conversion of starting materials to key products, with high activity and selectivity, is of great importance. To establish the catalyst structure correlation with activity and selectivity, fundamental understanding of the catalytic material is needed and how it performs under ‘in situ’ conditions.” 

If it can be established what properties of these catalysts lead to better performance, Dr Fadlalla says,  later iterations of catalyst development could follow a targeted-design approach (where desirable catalytic properties are engineered), significantly speeding up the process of finding viable catalysts, 

 “A key area of investigation is the effect of alloying in these materials on performance. This is also one of the most challenging phenomena to study using laboratory equipment due to limitations of the available characterisation methods. Multiple in situ characterisation techniques are needed, including synchrotron radiation which is where our experiments at Diamond are invaluable.” 

In situ characterisation through state-of-the-art synchrotron techniques 

Access to synchrotron radiation methods made possible through START and Diamond, plays a pivotal role in offering techniques that can provide resolution far beyond that available using laboratory-scale equipment, as well as world-leading expertise and collaborations.  

The UCT researchers visited Diamond in early December 2019 together with collaborating scientists from Southampton University².  Using Diamond’s B18 beamline, they were able to study the influence of substituents in the ferrite structure on the reduction behavior and carbon dioxide hydrogenation reaction to valuable products (e.g. fuels) and achieved all the planned experiments.  

 “In situ tests involve creating the conditions the catalysts would operate in to examine how they would be affected by the environment,” explainsProfessor Michael Claeys, who heads up UCT’s Centre of Catalysis and South Africa’s DST-NRF Centre of Excellence in Catalysis, c*change. “We need to extend the lifetime of the catalyst for as long as we can, as cost effectively and efficiently as we can. Therefore, a lot of what we do is about understanding: why my catalyst behaves as it does? Why is this catalyst more active than another one? Why is it more selective? The Diamond synchrotron makes answering these questions possible.” 

More about the collaborations on this project 

START cements the existing collaboration between Dr Fadlalla and Chris Mullins’ research group under Professor Michael Claeys, together with UK based collaborators, including START Co-I, Dr Peter Wells, Dr Khaled Mohammed and Dr Donato Decarolis of Southampton University. This collaboration played a key role in carrying out the synchrotron-based experiments and data analysis for the investigating CO₂ hydrogenation project.  

The research includes collaboration with Dr Michael Higham from Richard Catlow’s group at Cardiff University’s Catalysis Institute, who recently visited UCT on secondment funded by GCRF_START and is assisting with theoretical aspects of the research through computational chemistry calculations on the catalytic systems used.  

Related articles: https://start-project.org/2020/04/24/new-collaboration-opportunities-for-computational-insights-into-catalysis/