Computational Modelling of the Formation and Stability of Supported Particles of Catalytic Importance

Lead Research Organisation: Cardiff University
Department Name: Chemistry

Abstract

Since modern society demands a higher quality of life base on efficient technology and clean energy, contemporary scientists focus on new materials with particular properties performing under environmental friendly conditions. Structures of less than 100 nano-meters in size present different properties from those of bulk materials. This scale has opened new research boundaries in a growing field, with wide-ranging implications. For example, current industries use nano-materials during the fabrication of a large number of everyday-products. In chemical industries these fine particles are commonly dispersed metals on support materials reducing the cost and waste yields during product manufacture. However, scientists follow primarily a ''mix and try'' approach for the synthesis because of the complexity of the formation process and stability nano-structures, which are affected by multiple parameters, such as temperature, pressure and metal precursor.
Particle performance is dependent on their size and shape. Therefore we aim to identify computationally the thermodynamic and kinetic descriptors affecting the growth and stability of metal particles supported on specific surfaces. This project will allow us to unravel the effects of the support, the metal and the size of nano-particles while considering e.g. particles shape and diffusion across the surface, which will help to understand processes such as sintering and deactivation of the catalyst under working conditions. In particular, we propose to combine a number of late transition metals with well-characterised surfaces because of their importance in industrial catalysis and the extensive experimental data available.

The first goal of this challenging task is to understand the mechanism needed to build stable clusters from where the particle will grow. We will study the particles' interaction and diffusion on the surface and the feasibility of nearby particles to agglomerate. The second major goal is to identify the parameters modifying the growth processes along particular directions leading to different particle shapes such as sheets, wires, flakes. The reactivity of these structures will also be evaluated against common molecules such as molecular oxygen and water as both are present in oxidation reactions and in energy harvesting systems. The activity towards the activation and dissociation of molecular oxygen is important for reducing industrial waste related with oxidation processes. The last goal is to combine the previous results in a kinetic model to predict a durable nano-structure with applications in industry and energy technologies.

We will carry out this investigation in an effective and reliable way by combining a range of informatics tools which provide atomic-level resolution of the nano-structures and the supporting surface with accurate details e.g. oxidation state of the metal at the interface with the support. The combinations of these computational methods will allow us to study the factors controlling nucleation, growth and the shape of the supported metallic particles. The results will be validated by our experimental partners in the Cardiff Catalysis Institute and at the UK Catalysis Hub. With the success of this innovative research, we will provide detailed understanding of the parameters controlling the sintering of supported structures leading to undesirable properties e.g. loss of catalytic performance. The knowledge derived from this research is applicable to many chemical industries and academic researchers. We will disseminate the work across a wide range of fields. Within Cardiff Catalysis Institute and the assistance provided by association with the UK Catalysis Hub, we will outreach and engage the public which will be of importance in a project on such a topical theme.

Planned Impact

The ability to design and optimise supported nano-structures will have impact in a variety of areas, from academic and industrial research to the general public. In the short term, the outcomes of this project will benefit academic researchers (as outlined in the "academic beneficiaries" section), as well as chemical industries involving nano-structures either in the product manufacture or waste management. In a longer term, the understanding of the particle formation and stability on a support will provide strong basis for the design of nano-structures with applications in a widespread range of fields such as healthcare, sustainable materials, information handling, and energy harvesting and storage, being the wide society the ultimately end-user.

The knowledge resulting from the project will have an impact on materials and catalytic scientists, who will value not only the atomic level properties of the catalyst but also the methodology and scientific techniques developed during this project. We will contribute to the development of well-defined structures on-demand, which will make a distinctive contribution to the whole domain of catalysis. Our work will align to this priority and will interact strongly with the Cardiff Catalysis Institute and the UK Catalysis Hub, which will assist with the dissemination of the work and the development of impact.

Although our research is based on a solid base of fundamental understanding of the design, synthesis and performance of new catalytic materials, the outcomes will be of commercial interest related with the necessity of optimised particles for specific applications. For example, mono-dispersed nano-structures and their stability are areas of great strategic importance to the chemical industry with the potential for fostering long-term industrial engagement. Indeed, given progress with the science proposed, we anticipate subsequent stages involving the design of efficient devices, their scale-up and testing in direct collaboration with industrial users.

In the long-term, the proposed research programme will also assist the energy and environmental security. This ultimate goal will be achieved by enabling the development of novel technology devices with potential applications for improving energy harvesting and waste reduction.

The development of technical expertise during the project will impact on scientists in a variety of fields, as well as benefit the PI's, PDRA and PhD career development.
 
Description We have found a methodology to predict the morphology of small-medium Au nanoparticles on MgO, graphite and CeO2, which was the main objective of the project. We have also found a very weak interaction of Au and C, medium interaction on MgO and strong interaction with CeO2. It this interaction that defines the morphology of the particles, i.e. flat and pyramid. Indeed, on MgO and C, the Au structures are flat while on CeO2 is a pyramid in agreement with the cohesive/adhesion energies ratio. Ostwald ripening has been also studied and found not strong barriers in absence of stabilisers on MgO and C supports.
Exploitation Route We are preparing further proposals, this time in full collaboration with experimentalists, to study the effect on the particles morphology interacting with gas and liquid under reaction conditions. This will have an important impact in industries employing nanocatalysts as it will help to determine their lifetime.
Sectors Chemicals,Energy,Environment

 
Description Computational Modelling of the Formation and Stability of Supported Particles of Catalytic Importance
Amount € 2,500 (EUR)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 02/2018 
End 05/2018
 
Description HPC-Europa3 Student Exchange with Genoa University 
Organisation University of Genoa
Department Department of Chemistry and Industrial Chemistry
Country Italy 
Sector Academic/University 
PI Contribution A PhD student from my group visited Prof Riccardo Ferrando for almost 3 months funded by the HPC-Europa3. We established a collaboration where we provide DFT studies on metallic nanoparticles of realistic size.
Collaborator Contribution The PhD student developed skill in interatomic potentials by simulating supported nanostructures, in line with her thesis, under the supervision of a worldwide expert on the topic.
Impact Publication under preparation
Start Year 2018
 
Description Understanding Sintering of Co-based Catalyst for Syngas Reaction into Chemicals 
Organisation University of Cape Town
Department Department of Chemical Engineering
Country South Africa 
Sector Academic/University 
PI Contribution During the Fischer-Tropsch reaction, many species and phases may be formed and catalyse the process, among them the Co oxides have been detected experimentally. As part of this collaboration, we have developed a unique setup to model metallic Co and Co oxides structures implemented in standard periodic DFT simulations. It provides accurate results on the electronic structure and mechanical properties of Co, CoO and Co3O4.
Collaborator Contribution Our experimental partners at Cape Town University have provided the detailed characterisation of the supported structures, for instance, the fcc phase of metallic Co instead of the most stable hcp crystal structure at macroscopic levels. They have also studied the change of magnetic phase (from metallic Co to Co oxides) along the FT reaction which helped us to investigate the phase transitions (work in progress).
Impact We have participated in several outreach events and this work has been presented. Publication in preparation.
Start Year 2017
 
Description Invited Lectures 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I held invited talks in Xiamen (China) and Queretaro (Mexico) in the departments of Chemistry. The titles are "Accelerating Catalytic Process Understanding using Computer Simulations" and "Global Faculty Week" respectively.
Year(s) Of Engagement Activity 2017
 
Description Seminars / Lectures 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Study participants or study members
Results and Impact I have promoted research taking place in my group in seminars and lectures to a specialised public. The duration of the talks depended on the length of the workshop there were a follow up with questions and answers.
Year(s) Of Engagement Activity 2017