Structure and reactivity of titanium-platinum and titanium oxide-platinum interfaces

Pt supported on TiO₂ is famous as the first catalyst that revealed the “strong-metal support interaction” (SMSI) in methanation and methanol production from CO+H₂. It was observed that the amount of CO and H₂ that chemisorbed onto the Pt/TiO₂ surface under high-temperature reducing conditions was significantly diminished.; Studies here were designed to help understand SMSI in Pt/TiO₂ catalysts at an atomic level. Our approach was to create model systems by preparing ordered Ti/Pt(111) and Ti/Pt(100) alloys and studying CO and H ₂ chemisorption on these surfaces. Further, we investigated how oxidizing these alloy surfaces could lead to formation of ordered TiO_x structures on Pt(100) and Pt(111). These studies will help lay the ground work for atomic level design of surfaces with desirable properties. In these studies, we utilized several surface analytical techniques.; Composition and structure were characterized by alkali ion scattering spectroscopy (ALISS), X-ray photoelectron diffraction (XPD), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). Reactivity was probed by examining the chemisorption behavior using temperature programmed desorption (TPD).; We found that for both the Ti/Pt(111)-(2 x 2) and Ti/Pt(100)-c(2 x 2) alloys, the top surface is composed of pure Pt, with 25% Ti and 50% Ti in the second layer of each, respectively. Alloying with Ti reduces the reactivity of Pt for adsorbing CO and H₂. XPS revealed a chemical shift in the Ti/Pt(100)-c(2 x 2) alloy for the Ti 2p peak of 1.5 eV to higher binding energy than that of a thick Ti film. XPS also showed that the Ti 2p peak from the Ti/Pt(111)-p(2 x 2) is shifted by 1.4 eV to higher binding energy than that of a thick Ti film, thus indicating a strong electronic interaction due to alloying.; Oxidizing a Ti/Pt(100)-c(2 x 2) surface alloy with O₂, O ₃, or NO₂, produced ordered TiO_x structures on Pt(100) surfaces. A rich diversity of structures could be created using different annealing temperatures and Ti coverages. In the case of a Ti/Pt(111)-p(2 x 2) surface alloy, we found that NO₂ provided a sufficient oxygen coverage on the surface at room temperature to form TiO_x on Pt(111), but O₂ did not.