Ti/CeOx(111) interfaces studied by XPS and STM

Low coverage of Ti was deposited on the well-ordered CeOx(111) (1.5 < x < 2) thin films grown on Ru(0001) by physical vapor deposition at room temperature. The structure and interaction of Ti/ceria interfaces were investigated with X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) techniques under ultrahigh vacuum conditions. XPS data indicate that the deposition of Ti on both oxidized and reduced ceria surfaces causes the partial reduction of Ce from + 4 to + 3 state. Ti is formally in the + 4 state. STM data show the formation of small atomic-like titania features at 300 K, which coalesce to form chain structures upon heating. It is demonstrated in the study that the deposition of Ti can form mixed metal oxides at the interface and modify both electronic and structural properties of the ceria support. The structural study of Ti/ceria interfaces can be a key for understanding the higher catalytic activity of the Ti–CeOx mixed oxide catalysts as compared with the individual pure oxides.