Synthesis, Characterisation, and MD Investigation of the Mechanical and Catalytic Properties of Ceria Nanocubes and Ceria-Aerogel Nanocomposites

Nanoceria has become a widely used component in catalysis due to its unprecedented ability for oxidation/reduction. Irreversible deformation however plagues the operation of these materials, extinguishing their catalytic properties, and therefore they need protecting from harsh operating conditions. Furthermore, particle agglomeration can cause loss of catalytic activity. Here, two solutions to protecting nanoceria are presented, utilising both experiment analysis and atomistic molecular dynamic (MD) modelling. In particular how the use of sacrificial materials can protect a ceria nanocube, allowing stress of 40 GPa, in comparison to 2.5 GPa unprotected, before plastic deformation occurs, and how encapsulating ceria nanocubes in an aerogel matrix can prevent aggregation, retaining catalytic activity, and also act as a sacrificial material to prevent mechanical wear.

A ceria nanocube synthesis was optimised and Lanthanum introduced as a dopant with the aim of improving the catalytic activity of the ceria nanocubes by promoting the formation of oxygen vacancies (Chapter 3). The resulting nanoparticles were encapsulated in an aerogel host matrix, forming nanocomposites, with the aim of preventing aggregation. L3 edge HERFD-XANES was used to investigate the oxidation/reduction ability of the ceria nanocubes and nanocomposites under different operating temperatures (Chapter 4). This presented improved catalytic performance in ceria nanoparticles dispersed in an aerogel matrix, with further improvement indicated with the presence of a La-dopant.

An amorphisation-recrystallisation technique was employed for the atomistic MD investigation of sacrificial barriers (Chapter 5), which was further developed to include temperature variations, compression rate, and a calculated dynamic surface area (Chapter 6). This demonstrated that sacrificial barriers can allow for higher applied stress in a system before plastic deformation occurs, preserving the structural integrity. Dynamic surface area calculations presented stress-strain data in high concordance with experiment, whereas increased system temperature presented a reduction of measured stress, and compression rate variation presented further clarity of individual deformation events.

Furthermore, a new technique for the MD simulation of SiO2 aerogel was developed (Chapter 7), where a seed and cluster growth method was employed to form the aerogel, then uniaxial force was applied to investigate the resulting mechanical properties.