Thermodynamic Evolution of Cerium Oxide Nanoparticle Morphology Using Carbon Dioxide

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 favour enhanced cube-like morphologies.

Role of Low-Coordinated Ce in Hydride Formation and Selective Hydrogenation Reactions on CeO2 Surfaces

“…Hutter et al 58 obtained an adsorption energy of 0.31 eV for CO 2 on the CeO 2 (111) surface, which is much lower than the adsorption energy of 1.48 eV that we calculated for the CO 2 on the CeO 2 (223)-Ce-t surface. Molinari and Parker et al 59 obtained an adsorption energy of 0.5 eV for CO 2 at CeO 2 (111), which is relatively close to that reported by Hutter et al 58 These results indicated the important role of the low-coordinated Ce in stabilizing the adsorbed CO 2 , which was also noted by the recent studies at various other CeO 2 facets. 59 The calculated adsorption energy of H 2 on the CeO 2 (223)-Cet surface is 0.10 eV (Figure 7).…”

DFT + U Study of Strain-Engineered CO2 Reduction on a CeO2–x (111) Facet

“…The energy diagram for the reaction path under strain can be seen in Figure , where it is seen that the strain affects the vacancy formation energy to the greatest extent and the transition state to a less extent and the adsorbed CO with no large Ce 3+ , while the adsorbed CO 2 – has one Ce 3+ and the energy change caused by strain is approximately half that of the oxygen vacancy. It should be noted that at the elevated temperatures in SOEC cells, we find that CO 2 adsorbed as CO 3 2– is unstable on reduced CeO 2 (111) in agreement with Symington et al…”

“…The most favorable adsorption of CO 2 on the CeO 2 (111) surface is to a surface oxygen to form tridentate carbonate with an adsorption energy of −0.17 eV on the reduced surface. The atomic structure of tridentate carbonate is shown as state (3b) in Figure .…”

Effects of high-temperature CeO2 calcination on the activity of Pt/CeO2 catalysts for oxidation of unburned hydrocarbon fuels

“…[19][20][21][22] There are two possible reasons for the much lower surface carbonate concentration on CeO 2 (800): (1) the high temperature calcination (800 °C for 10 h) decreases the amount of surface defects; (2) CeO 2 (800) predominantly exposes the (111) facet which is much less favorable for CO 2 adsorption in comparison to the (100) and ( 110) facets. 23 The lower surface defect density on the high temperature treated sample was further confirmed by XPS. Fig.…”