Speaker
Description
We will consider the case of cerium dioxide, an important material in water gas shift reactions, three-way catalysis, soot oxidation, and enzyme mimetic activity (nanozymes). In such catalytic applications, the performance of the catalyst is dependent on the morphology of the nanoparticle. Control of size and morphology of nanoparticles is therefore key for the design of energy and catalytic materials as it significantly affects the surface composition, reactivity and selectivity. As different surfaces show different catalytic activity, the nanoparticles should be shaped to express those surfaces with enhanced activity. Although synthesis can achieve selective control, a key challenge is to identify strategies to enhance the expression of catalytically active surfaces and to prevent their disappearance over many catalytic cycles. Here, we use density functional theory to predict the surface composition and energetics of cerium dioxide {111}, {110} and {100} surfaces in the presence of water, carbon dioxide and hydrogen peroxide. We found that there is a strong chemical adsorption of all species. Whereas water and hydrogen peroxide display dissociative adsorption, carbon dioxide forms surface carbonates. The strength of the adsorption is surface dependent, and generally it follows the order {100} > {110} > {111}. Using a thermodynamic strategy, we then calculate the surface free energy of adsorbed surfaces as a function of external conditions. This allows us to predict changes in the equilibrium nanoparticle morphology following changes from octahedral, truncated octahedral and cuboidal shapes as a function of temperature, water and oxygen partial pressure.
