Cerium oxide is a principal component in many heterogeneous catalytic processes. One of its key characteristics is the ability to provide or remove oxygen in chemical reactions. The different crystallographic faces of ceria present significantly different surface structures and compositions that may alter the catalytic reactivity. The structure and composition determine the availability of adsorption sites, the spacing between adsorption sites and the ability to remove O from the surface.

 

To investigate the role of surface orientation on reactivity, CeO2 films were grown with two different orientations. CeO2(100) films were grown ex situ by pulsed laser deposition on Nd-doped SrTiO3(100). The structure was characterized by RHEED, XRD and reflectometry. CeO2(111) films were grown in situ by thermal deposition of Ce metal onto Ru(0001) in an oxygen atmosphere. The structure of these films has been studied by LEED and STM. Attempts to grow CeO2(100) in situ by physical vapor deposition on Pt(100) and Pd(100) failed due to preferential growth of CeO2(111) on these supports.

 

The chemical reactivity was characterized by the adsorption and decomposition of various molecules such as methanol, water and acetaldehyde. Reaction products were monitored by TPD and surface intermediates were determined by soft x-ray photoelectron spectroscopy. In general the CeO2(100) surface was found to be more active, i.e. molecules adsorbed more readily and reacted to form new products, especially on a fully oxidized substrate. However the CeO2(100) surface was less selective with a greater propensity to produce CO, CO2 and water as products. The differences in chemical reactivity are discussed in light of possible structural terminations of the two surfaces.

 

Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy. Portions of this work were conducted at the National Synchrotron Light Source, Brookhaven National Laboratory, and Oak Ridge National Laboratory's Center for Nanophase Materials Sciences, which are sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.