Surface-dependent oxidation of H2 on CeO2 surfaces

In this study, ceria nanoparticles with well-defined surface states were synthesized in order to enable the study of different ceria surfaces, independently. Ceria nanocubes were shown to expose only (1 0 0) surfaces, ceria nanooctahedra only (1 1 1) surfaces, and ceria nanorods are more complex, with at least 50% of (1 1 0) surfaces, as shown by high-resolution transmission electron microscopy. Temperature-programmed reduction (TPR) by hydrogen performed on these powders shows the following order of reaction temperatures: cubes < rods < octahedra. Moreover, activation energies associated with the first surface reduction in each sample show a similar trend. Ceria (1 0 0) surface is the most reactive toward hydrogen oxidation, while (1 1 1) surface is the less reactive, and (1 1 0) surface has likely an intermediate behavior. These results confirm that hydrogen oxidation is highly surface-dependent and that a strong attention must be paid to the surface state of the catalyst in these devices.