Modification of active sites on YSZ(111) by yttria segregation

The surface properties of YSZ (111) have been investigated by X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), temperature programmed desorption (TPD) of adsorbed formate, and computational studies using the ReaxFF reactive force field approach. XPS and computer simulations showed enrichment of the surface with yttria. STM studies indicated that a high density of step edges are readily formed with ∼35% of the surface sites located at steps. Step edges are identified as the primary adsorption sites for formate. The formate oxidizes in a dehydration reaction producing carbon monoxide and water at ∼600 K. This is contrasted to the reaction of formate on pure zirconia where formate reacts by both dehydration and dehydrogenation reactions. This shift in the selectivity between pure zirconia and yttria-doped zirconia is attributed to the modification of the active step edge sites by yttria segregation. Therefore, the modification of active sites by minority species in a mixed oxide can control the chemical surface functionality.