Growth and Reactivity of CeO2(100) Thin Films

CHEN, TSUNG-LIANG; CALAZA, FLORENCIA C.; OVERBURY, STEVEN H.; BIEGALSKI, MICHAEL D.; CHRISTEN, HANS M.

Albuquerque, NM

Simposio; Avs 57th International Symposium and Exhibition; 2010

Amercian Vacuum Society

4:00pm AC+TF-MoA7 (Oral - Co-author) AC+TF-MoA7 (Oral - Co-author) 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 methanol and 2-propanol. Reaction products were monitored by TPD and surface intermediates were determined by soft x-ray photoelectron spectroscopy and infrared spectroscopy. Both of these alcohols readily chemisorbed on either surface in UHV. The decomposition of methanol was less selective on CeO2(100) than on CeO2(111) with CO and H2 resulting even from a fully oxidized surface. Water was also produced as on CeO2(111), and the CeO2(100) surface could be reduced by exposure to methanol at 700 K. Unlike on reduced CeOX(111), methanol adsorption on reduced CeOX(100) produced only a small increase in reactivity and inhibited formaldehyde formation. 2-propanol produced primarily propene and water with a small amount of acetone.