The drive to design new materials with surprising capabilities is a fast-moving frontier of research – and computers are well-established as a crucial tool in accelerating progress.
The TOUCAN collaboration, including SES members King’s College London, the University of Oxford and University College London, has shown how modelling & simulation can aid the design of nanoscale catalysts capable of speeding up key chemical reactions used in a range of industrial processes.
Harnessing the skills of researchers such as Dr Francesca Baletto of King’s, TOUCAN has taken the first steps on a journey that could see industry develop remarkable new catalysts made from metal-alloy nanoparticles – and help deliver big advances in the development of low-temperature fuel cells, CO2 storage and other vital fields.
The nano-world is a curious place. At scales of less than 100 billionths of a metre – the realm of single molecules and atoms – materials can do unexpected things. Platinum is a good example. Magnetism isn’t normally one of its properties, yet nanoparticles of platinum are magnetic.
Such behaviour is of particular interest to industry. Take, for example, alloys made from nanoparticles of two or more metals. The fact that these ‘nano-alloys’ exhibit different physical and chemical properties from the same materials at a larger scale makes them prime candidates to act as innovative, improved industrial catalysts. But relying on physical experiments to explore countless configurations and their capabilities, and identify promising candidate alloys, poses huge challenges from a time/budget perspective.
“Modelling & simulation offers a much less resource-hungry way of studying potential nano-alloys, their intrinsic properties and how their shape and structure affect their behaviour,” says Francesca Baletto, who works in the Theory & Simulation of Condensed Matter Group at King’s. “The TOUCAN team set out to use such tools to identify ‘magic’ nanoparticles with surprising properties and develop a deeper understanding of them, as an initial step towards the ultimate Holy Grail: developing the equivalent of a genome of a nanocatalyst, a template that would enable industry to design nanocatalysts fast and efficiently.”
A 5-year EPSRC-funded initiative involving the Universities of Birmingham and Cambridge as well as the SES members, TOUCAN (Towards an Understanding of Catalysis on Nano-alloys) has provided a foundation for future use of computational tools in designing and investigating the catalytic capabilities of nano-alloys made from two metals (e.g. platinum/nickel, platinum/gold, platinum/copper, silver/platinum, silver/gold) that can be tailored to particular needs.
Studying Structures, Predicting Properties
Drawing on the distinctive expertise of five institutions with different specialisms, TOUCAN has been hugely strengthened by the exchange of views, ideas and, in some cases, personnel among the collaborators. “I’ve worked particularly closely with colleagues from Birmingham and Cambridge,” Dr Baletto says. “But the entire TOUCAN team has worked towards a common goal: understanding complex nanoscale systems and predicting how their composition, geometry and size can be altered to change their properties and affect the reactions these catalyse. For instance, what exactly are the electrons in the nano-alloy doing, what are the implications in terms of how the nano-alloy behaves and how can we maximise the benefits of this for a specific application?”
Dr Baletto’s contribution has revolved around using modelling software such as LODiS to study metallic nanoparticles’ structural stability and to simulate physical processes such as melting and nucleation (the process whereby molecules in a liquid or gaseous state start to turn into a solid). “Sometimes, a nanoparticle’s geometry can change due to external factors such as temperature or pressure,” she explains. “That may even happen without any change from one state (solid, liquid or gas) into another. Understanding these processes is fundamental to exploiting metallic nanoparticles as catalysts, especially as they could be subjected to extreme conditions in industrial processes.”
Her work has shown, for instance, that the magnetism of clusters of platinum nanoparticles depends significantly on the particles’ shape. “Stretching a nanoparticle can make it more magnetic, while compressing it can reduce its magnetism,” says Dr Baletto. “Similarly, changing a nanoparticle’s structure can substantially affect, positively or negatively, its ability to adsorb molecular oxygen. Modelling & simulation can provide the accurate insights we need to penetrate questions like these.”
A Platform for Progress
The ability to predict promising nanocatalysts for specific applications is exactly what industry needs to aid its quest to optimise processes such as the breaking down of molecular oxygen and its ability to form water when reduced, a key step in the use of low-temperature fuel cells to meet energy needs in the decades ahead. Similarly, processes designed to break down methane (CH4) into carbon and hydrogen will be crucial to the continuing evolution of a thriving biomass industry, which will also play a central part in the greener energy landscape of tomorrow.
So as TOUCAN draws to its conclusion – and with key results already disseminated to the international catalysis community at a wrap-up workshop organised by the project team at the end of 2016 – what next?
“We need to generate awareness about how modelling & simulation can be a game-changer in the sphere of catalyst research, enabling us to elucidate the relationship between shape and properties.”
– Dr Francesca Baletto, King’s College London
“Over the next couple of years, we’ll be looking to collaborate with experimentalists in academia and involve at least one major British multinational chemicals company as we take things forward,” Francesca Baletto explains. “As well as sharing the insights we’ve achieved, we need to generate awareness about how modelling & simulation can be a game-changer in the sphere of catalyst research, enabling us to elucidate the relationship between shape and properties. Our hope and expectation is that, within four or five years, we can begin to see this research reaping real benefits – with real-world benefits, in the shape of significantly more efficient industrial processes, following not too far behind.”
Dr Francesca Baletto
King’s College London
- G.G. Asara, L.O. Paz-Borbon and F. Baletto (2016). “Get in Touch and Keep in Contact”: Interface Effect on the Oxygen Reduction Reaction (ORR) Activity for Supported PtNi Nanoparticles. ACS Catal. 6 (7), pp.4388-4393.
- J.B.A. Davis, F. Baletto and R.L. Johnston (2015). The Effect of Dispersion Correction on the Adsorption of CO on Metallic Nanoparticles. J. Phys. Chem. A 119 (37), pp.9703-9709.
- A.L. Gould, K. Rossi, C.R.A. Catlow, F. Baletto and A.J. Logsdail (2016). Controlling Structural Transitions in AuAg Nanoparticles through Precise Compositional Design. J. Phys. Chem. Lett., 7 (21), pp.4414-4419.
- Di Paola, R. D’Agosta and F. Baletto (2016). Geometrical Effects on the Magnetic Properties of Nanoparticles. Nano Letters 16, pp.2885-2889.
- Rossi and F. Baletto (2017). The Effect of Chemical Ordering and Lattice Mismatch on Structural Transitions in Phase Segregating Nanoalloys. Phys. Chem. Chem. Phys. 348, pp.11057-11063.
Pt-clusters of 13 atoms embedded in a zeolite pore. Two distinct shapes show a different total magnetisation, from 2 to 8 Bohr magneton, and a characteristic spin density difference, more spherical for high magnetisation. The latter can be exploited for magnetic storage.
Oxygen adsorption on PtNi clusters. The picture illustrates the variety of active sites seen by an oxygen molecule. The complexity of the surface sites available for an adsorbate is well reproduced by a generalised coordination number.