Thermodynamic Evolution of Cerium Oxide Nanoparticle Morphology Using Carbon Dioxide
Adam R. Symington, Robert M. Harker, Mark T. Storr, Marco Molinari, Stephen C. Parker
Abstract
Surface morphology is known to affect catalytic activity, as some surfaces show greater activity than others. One of the key challenges is to identify strategies to enhance the expression of such surfaces and also to prevent their disappearance over time. Here, we apply density functional theory to the catalytic material CeO2 to predict the effect of adsorbed CO2 on the morphology of the material as a function of temperature and pressure. We predict that CO2 adsorbs as surface carbonates and that the magnitude of the adsorption energy is surface dependent, following the order {100} > {110} > {111}. We show that this difference leads to selective thermodynamic enhancement of {100} surfaces as a function of CO2 partial pressure and temperature. Finally, we show how the calculated surface free energies as a function of external conditions can be deployed to predict changes in the equilibrium particle morphology. These include the prediction that ceria nanoparticles prepared in the presence of supercritical CO2 will favor enhanced cubelike morphologies.