“The GCRF START grant has been an excellent opportunity to support UK and international computational research, enabling engagement with experimentalists both within and outside of the START community. Membership of the START network enables us all to benefit from the wider networks we partner with globally, bringing scientists and research closer together, no matter where we are based. I hope to continue to build on the research links forged in Europe, Africa, Australasia, and Asia.” – Dr Michael Higham, Cardiff University (UK) and UK Catalysis Hub
Addressing emissions-linked climate change using electricity produced from renewable sources can present some complex challenges. One of these is the requirement that nations construct extensive electrical infrastructures, something which may be problematic for some developing nations. On the other hand, clean and sustainably produced liquid combustible fuels can be readily adapted for use in existing infrastructures based around gasoline fuel. To this end, scientists are conducting studies combined with carbon capture technology, photocatalytic water splitting, and catalytic processes to convert methanol to hydrocarbons. The aim is to develop a “synthetic” carbon cycle that mimics nature (albeit on much faster timescale), instead of the burning of fossil fuels which takes place at a rate which far exceeds that which nature can cope with.
Dr Michael Higham is a GCRF START Postdoctoral Research Assistant (PDRA) and an Associate of the UK Catalysis Hub – a consortium of universities involved in catalysis research led by Cardiff, Bath and Manchester universities. Based at Harwell’s Research Complex in Oxfordshire and until recently, a PDRA at Cardiff University, Michael brings his expertise in computational modelling to projects that focus on developing catalytic processes for more effective clean fuel production, minimisation and valorisation of waste byproducts, and reducing harmful gaseous emissions. These projects stretch across several research networks within the UK and further afield.
Copyright and image credit: Michael Higham
The growing global interest in developing a new carbon cycle by enabling sustainable liquid combustible fuels ties in with Sustainable Development Goals (SDGs) for Energy (SDG 7) and Climate Action (SDG 3), Industry, Innovation, and Infrastructure (SDG 9). The goal of Reduced Inequalities (SDG 10) is also supported through making clean, sustainable energy more accessible to developing nations, rather than the preserve of the wealthiest countries. By enabling the development of a range of clean energy technologies (such as synthetic combustible fuels, photovoltaics, battery technologies, and others), different nations with varying economic and geographical circumstances can aim to adopt technologies suited to their needs. This links with the Goal for Sustainable Cities and Communities (SDG 11) by making sustainability an accessible and achievable goal for all.
Providing computational insights for experimental work utilising the synchrotron facilities at the UK’s national synchrotron, Diamond Light Source (Diamond), Michael works closely with Professor Sir Richard Catlow, Foreign Secretary of the Royal Society, GCRF START Co-I and Professor at the UK’s University College London (UCL) and Cardiff University. Their aim is to gain a better understanding of catalyst systems for CO2 valorisation, which is the conversion of waste pollutant gas into clean fuels for clean and affordable energy application. This research concerns improving understanding of catalytic processes on an atomic scale by using computational methods to explore catalysts for methanol synthesis and Fischer-Tropsch synthesis, which are important processes to convert CO2 (a contributor to global warming and a product of burning fossil fuels) into combustible liquid fuels.
Michael has seen several successful publications involving his work which have been made possible through the GCRF START grant. These include a detailed and exhaustive computational investigation of the mechanism of CO2 conversion to methanol over copper surfaces, published in Dalton Transactions1 in May 2020. In this work, the powerful computational tools available in Density Functional Theory (DFT) techniques were applied to investigate all possible mechanistic routes for this reaction, elucidating the elementary processes in this reaction, thus informing, and providing an investigative framework for ongoing investigations into the more complex copper / zinc oxide (Cu/ZnO)-based systems, which is more representative of industrial methanol synthesis catalysts.
Shedding light on, and corroborating macro-scale observations – collaborations in the UK and Australia
Additionally, Michael has contributed to a joint publication with experimental colleagues from the UK’s Catalysis Hub team, the University of New South Wales (UNSW), and RMIT University, Australia, investigating thermo- and photo-catalytic processes in CO2 conversion to methanol over alumina (Al2O3) supported Cu/ZnO catalysts. Published in Nature Communications2 (March 2020), this research explores a synergistic mechanism (i.e. involving active participation of both the Cu and ZnO components of the catalyst, rather than ZnO merely acting as an inert support material) for CO2 conversion taking place at the Cu/ZnO interface, with DFT calculations being applied to assist the rationalisation of experimental valence band spectra, which can provide useful insights into the electronic structure of catalyst materials and potentially explain observed catalytic activity.
Further computational investigations have been conducted to better understand the role of reconstruction of polar ZnO surfaces in determining the morphology of supported Cu clusters, employing unbiased Monte Carlo global optimisation techniques to obtain the most stable structures for small Cu clusters supported on stable ZnO surfaces, which will enable subsequent studies to model elementary surface processes using surface models that are realistic and representative of typical Cu/ZnO catalysts. The work was published in October 2020 in the Journal of Materials Chemistry A3.
Through an ongoing collaboration with Dr Michael Stamatakis (University College London), Michael is busy extending the work published in the Dalton Transactions paper by conducting kinetic Monte Carlo simulations (which rely on random sampling of a probability distribution obtained from the previously conducted calculations published in the Dalton Transactions paper, in order to elucidate macroscopic kinetic behaviour based on atomistic simulations) for the metallic Cu systems investigated previously to obtain novel insights into the impact of reaction conditions, such as temperature and pressure, on the reaction mechanism and product distribution.
Furthermore, additional ongoing collaborations with Dr Rosa Arrigo (University of Salford) and Dr Matthew Quesne (Cardiff University) are exploring the mechanism of the electrocatalytic reduction of CO2 over bimetallic Cu/Zn systems, with computational insights supporting experimental in situ X-ray absorption spectroscopy studies undertaken at the Diamond synchrotron. It is intended that both collaborations will result in high-impact publications in leading, internationally recognised journals.
UK-Africa partnerships and atomic scale perspectives
“As long as there is funding for us to do research, we are going to build collaborations, and this provides a great deal of added value. By bringing African and UK researchers together, there is a greater opportunity for UK, European and African research networks to overlap and integrate. As we have seen from several successful collaborations, this is the wider impact of the GCRF START grant.”
Dr Michael Higham, UK Catalysis Hub and Cardiff University
Through the START network, Michael works with colleagues in Africa on studies ranging from investigating adsorption induced magnetisation changes in nickel catalysts, to research into bimetallic catalysts for CO2 hydrogenation of environmental and industrial importance. Using computer simulations and modelling to shed light on, and corroborate macro-scale observations in actual experiments, atomic scale information is possible that might otherwise be difficult to measure in situ.
One example is the experimental results from Michael’s collaboration with Professor Michael Claeys Dominic De Oliveira at UCT’s Centre for Catalysis and South Africa’s DST-NRF Centre of Excellence in Catalysis – c*Change. This collaboration began in 2019 during Michael’s GCRF START grant-funded secondment to UCT. The project explores the effect of adsorption on magnetisation of Ni surfaces and will be featured in a manuscript the team are preparing for submission in the coming months. The overarching aim is to use computational work to valorise the new techniques in Dominic’s experimental work using UCT’s Centre for Catalysis’ unique in situ magnetometer – a tool that few other institutions have access to. This work is important because it demonstrates how changes in magnetisation of catalyst nanoparticles can vary under real reactionary conditions such as high pressure and high temperature and is a good way to see what is happening on the catalyst’s surface in a way that allows the reproduction of industrial conditions.
“When it comes to computational aspects of chemistry, one has to spend a great deal of time looking at how we might model catalyst surfaces and think about what questions to ask as these are complex, multi component systems” says Michael. “We can test hypotheses for explanations of observed real-world behaviour, and on the flipside, we can use what we already know about well-studied systems to examine new, novel materials, and therefore help to direct future experimental studies.”
“We are going to focus initially on the impact of hydrogen and water species (H, O, OH, and H2O), on the surface magnetisation as Dominic already has plenty of experimental results for this from UCT’s in-situ magnetometer,” Michael adds. “The magnetometer is a really unique bit of kit and is a world’s first4. I also envisage a similar investigation looking at C-containing species relevant for Fischer-Tropsch synthesis, which we intend to result in an additional publication once we have enough experimental data. I am running a couple of additional calculations and writing my contribution to the manuscript in the coming weeks. Early indications show that there are changes in the magnetisation when conditions are varied.”
“If we can understand what is causing those changes in magnetisation, then we can investigate various species present on the catalyst’s surface, which is where the computational aspect comes in,” Michael explains. “I can look at the sort of species we might expect and test lots of different species on those surfaces and see what the calculations might suggest. Once we understand these, we can use this approach for other catalytic systems.”
Another example of UK-Africa collaboration is Michael’s work with Dr Mohamed Fadlalla and Christopher Mullins (UCT ‘s Centre of Catalysis and c*Change) on bimetallic alloy catalysts for methanol synthesis and conversion. This work also involves another UK group of catalysis researchers led by GCRF START Co-I, Dr Peter Wells from the University of Southampton’s Chemistry Department in the UK.
“In early December 2019, our team from the University of Cape Town and Southampton University visited the Diamond Light Source synchrotron and used the B18 beamline to study the influence of substituents in the ferrite structure on the reduction behaviour and carbon dioxide hydrogenation reaction to valuable products (e.g., fuels),” Mohamed Fadlalla says. “The next step is Michael’s computational work to help us to calculate certain insights from the results such as how the catalyst looks and how the reactant is interacting with the catalyst.”
The computational calculations will examine the catalytic product distributions which provide detailed insights into possible explanations for observed catalyst selectivity, as Michael explains below,
“Through modelling adsorption energies, activation energies and reaction energies we hope to shed light on what happens on the catalyst’s surface. We want to compare the observed, experimental data with the calculations. Mohamed has been doing a lot of very good experimental work. I hope to get more involved once they are in a position for me to complement their experimental work with my computational input, should they need my assistance.”
Michael adds,
“These partnerships are important for the African and the UK research communities, not least for knowledge exchange in the search for sustainable, clean energy sources to tackle climate change. What we have seen in our interactions with our African colleagues is that they do great science and innovation on a far lower budget than most developed countries despite facing greater funding challenges than we generally do. Their expertise is world-class, and we should therefore be supporting these groups and collaborating closely with them so that the benefit from such excellent research has international as well as local impact.”
Commenting on the collaboration with Michael Higham and START, Prof. Michael Claeys, Director of c*Change said,
“Computational experts like Dr Michael Higham can predict how certain catalysts perform and we can try to confirm that with our techniques which is a reciprocal learning process. This expertise informs us, and we inform them through the results which is something a single group can’t do because very specific expertise is needed. Collaborating provides some of the most powerful learning opportunities which really shape your people.”
Developing mentoring skills and teaming up with ‘virtual’ visiting students in Germany and Singapore
Michael Higham has also teamed up with ‘virtual’ visiting students David Jurado (in Germany) and Yong Rui Poh (in Singapore) – collaborations which have worked well despite the challenges posed by the Covid-19 pandemic and remote working. Michael reports that both students have been “performing excellently”, which is promising not only due to the science but also because this is the first time Michael has mentored and supervised students. Although both students started with little experience of computational work, they have gained experience and have many interesting results5. David was able to send his calculations remotely from Germany and Yong Rui Poh could log onto UK super computers from the other side of the world without leaving Singapore. They are currently working on determining transition states for some processes, but once this is complete, should be ready to write up the manuscripts. It is hoped, given the breadth and detail of this work, that two manuscripts will be submitted.
“David has completed his Master’s thesis and will remain as a PhD student in Prof. Ingo Krossing’s group at the University of Freiburg, Germany,” Michael explains. “We intend to continue to work with David and Ingo on David’s Doctoral research, with David having prepared an ambitious proposal for his PhD studies. Meanwhile, Yong Rui has concluded his studies at the National University of Singapore and will begin his PhD studies at University of California, San Diego, USA, with the potential for more collaboration in the future.
Commenting on what he has learnt from this collaboration, Michael says,
“This has been a positive and rewarding experience for me and shows how remote collaborations can be very fruitful. Thinking about follow on opportunities for START, I would be very happy to work with students at African universities in a similar way. If there is a reliable internet and a computer terminal, there is no reason why I couldn’t also assist and mentor students in Africa.”
Michael is now embarking on a new postdoctoral appointment with Prof. Sir Richard Catlow’s group at UCL working in collaboration with Prof. Justin Hargreaves (University of Glasgow) to investigate transition metal nitride catalysts for ammonia synthesis. He will remain based largely at the Catalysis Hub at Harwell, and whilst this involves some new projects, he fully intends for there to be continuity between his current work and START collaborations.
“We have put a lot of groundwork into our collaborations through START. Although the funding for these is currently uncertain, we will always do research with the best people for the projects we work on through the Catalysis Hub and others. Prof. Claeys’ group in Cape Town is an excellent group. Whatever happens, I see no reason why we wouldn’t continue these collaborations. They are some of the best in the field!”
“In closing,” Michael adds, “I want to thank Professor Richard Catlow who has been incredible to work with through the START network, not only as an eminent scientist but also as demonstrating the importance of networking which I have benefitted a great deal from and learnt from. I have, myself, had access to Richard’s very large network of researchers who I would otherwise have not had contact with.”
Professor Sir Richard Catlow comments,
“Michael’s work, while exploring exciting fundamental scientific problems is contributing to the key challenges which must be met if we are to achieve the goal of global sustainability. His projects, which are typical of the whole START community, also illustrate how modern science is a global activity bringing together scientists at all career stages and with complementary skill sets. The GCRF START initiative can be proud of what it has achieved.”
Footnotes
1 Mechanism of CO2 conversion to methanol over Cu(110) and Cu(100) surfaces. M. D. Higham, M. G. Quesne and C. R. A. Catlow, Dalton Trans., 2020, 49, 8478 DOI: 10.1039/D0DT00754D
2 Xie, B., Wong, R.J., Tan, T.H. et al. Synergistic ultraviolet and visible light photo-activation enables intensified low-temperature methanol synthesis over copper/zinc oxide/alumina. Nat Commun 11, 1615 (2020). https://doi.org/10.1038/s41467-020-15445-z
3 Morphology of Cu clusters supported on reconstructed polar ZnO (0001) and (000) Surfaces. M. D. Higham, D. Mora-Fonz, A. A. Sokol, S. M. Woodley and C. R. A. Catlow, J. Mater. Chem. A, 2020, 8, 22840 DOI: 10.1039/D0TA08351H
4 The in situ magnetometer can analyse ferromagnetic materials under actual operating conditions, including high temperature and pressure (500°C, 50 bar) with the ability to control gas and/or liquid flows through the material. This makes it an indispensable tool for advanced research and industrial catalytic process optimisation.
5 David has focused more on the CO2 hydrogenation mechanism via HCOO*, COOH*, HCOOH*, H2COO* and OCH2OH*, whereas Yong Rui has been looking at CO2 dissociation, and subsequent hydrogenation of the resulting CO* to HCO*, HCOH*, and H2CO*, as well as the processes that are common to both mechanisms (namely H2CO* hydrogenation to either CH2OH* or CH3O*, and the subsequent hydrogenation of these two species to give the product, methanol).