Direct evidence for the instability and deactivation of mixed-oxide systems: Influence of surface segregation and subsurface diffusion
Please cite this item using this persistent URLhttp://hdl.handle.net/11693/21715
Journal of Physical Chemistry C
- Research Paper 
In the current contribution, we provide a direct demonstration of the thermally induced surface structural transformations of an alkaline-earth oxide/transition metal oxide interface that is detrimental to the essential catalytic functionality of such mixed-oxide systems toward particular reactants. The BaO x/TiO 2/Pt(111) surface was chosen as a model interfacial system where the enrichment of the surface elemental composition with Ti atoms and the facile diffusion of Ba atoms into the underlying TiO 2 matrix within 523-873 K leads to the formation of perovskite type surface species (BaTiO 3/Ba 2TiO 4/Ba xTi yO z). At elevated temperatures (T > 973 K), excessive surface segregation of Ti atoms results in an exclusively TiO 2/TiO x-terminated surface which is almost free of Ba species. Although the freshly prepared BaO x/TiO 2/Pt(111) surface can strongly adsorb ubiquitous catalytic adsorbates such as NO 2 and CO 2, a thermally deactivated surface at T > 973 K practically loses all of its NO 2/CO 2 adsorption capacity due to the deficiency of surface BaO x domains. © 2011 American Chemical Society.