Observation of quantum effect of catalyst activity of Gold Nanoisland / MO_x

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In this research we studied gold-rutile catalyst has been observed by high-resolution transmission electron microscopy to clarify the active site of the catalysis on oxidation of CO gas. In previous studies, two active sites have been proposed. One is the periphery of the nano-gold particle and rutile substrate, where the oxygen atoms on the rutile substrate react dominantly with CO molecule. Another proposal for the activation site is the surface of nano-gold particle, on which gold and titanium atom forming specific orbitals make active the surface. We observed surface structures of rutile crystals after such procedures as heating, oxygen exposure and/or hydrogen exposure. Furthermore, we studied morphologies and interface structures of nano-gole particle and rutile crystal before and after the procedures described above. Through such investigations, we found to followings.(1)Rutile crystal has different facet strcutures, depending on the heating procedure in oxygen gas or in hydroge … More n gas. Oxygen gas expands (211) and (100) facets of the rutile crystalline surface that was prepared by air cleavge. Hydrogen gas expands (110) facet, the (211) and (100) facets being shrank. The hydrogen gas seems to make the rutile surface oxygen deficient, so that the surfaces after exposure were roughened by segregation of the titanium atoms. Subsequent exposure of oxygen gas on the hydrogen pre-exposed surface, the surface became smoother to restore its stoichiometry.(2)Adsorption of nano-gold particles on (110) rutile surface was studied in detaile. To prepare the (110) facet after oxygen exposure, we exposed the rutile surface to hydrogen gas at 1200 - 1300℃ and to oxygen gas at 700 - 900℃ subsequently. Nano-gold particles deposited on such oxygen-exposed-(110) facet did not wet to the substrate, having a little contact area.(3)Nano-gold particles deposited on the hydrogen-exposed-(110) facet wet well with the surface. Taking into segregation of titanium atoms on the surface account, the thin gold particles supposed to bond with titanium atoms or even to form alloy phase.(4)After heating such flat and thin gold particles, they were transformed into thick particles with less contact area with the rutile surface. Such morphology change is supposed to be oxidation of the rutile surface during the heating procedure.In summary, we found structure and morphology variation of the rutile surface and/or nano-gold particles, being caused by oxidation and reduction procedures of the surface without gold atom and with gold atom. Both titanium atom segregation under nano-gold particle and oxygen atom remaining at the periphery play active, in different way from previous proposals. Less