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

在本研究中，我们对金红石催化剂进行了高分辨率的电子显微镜观察，以明确该催化剂对CO气体氧化的活性中心。在以前的研究中，已经提出了两个活性位点。一个是纳米金颗粒和金红石衬底的外围，金红石衬底上的氧原子主要与CO分子反应。另一种激活位置是纳米金颗粒的表面，在其上形成特定轨道的金和钛原子使表面活跃。我们观察了金红石晶体经过加热、氧气暴露和/或氢气暴露等过程后的表面结构。此外，我们还研究了纳米Gole颗粒和金红石晶体在上述过程前后的形貌和界面结构。通过这些研究，我们发现：(1)金红石晶体在氧气和氢气…中的加热过程不同，具有不同的小面结构。更多的氮气。氧气使空气解理法制备的金红石晶面(211)和(100)晶面膨胀。氢气使(110)晶面膨胀，(211)和(100)晶面收缩。氢气似乎使金红石表面缺氧，从而使暴露后的表面因钛原子的偏析而变得粗糙。随后在氢气预暴露的表面上暴露氧气，表面变得更加光滑，恢复了其化学计量比。(2)详细研究了纳米金颗粒在(110)金红石表面的吸附。为了在氧气暴露后制备(110)面，我们将金红石表面暴露在1200-1300℃的氢气中和700-900℃的氧气中。在这样的曝氧-(110)面上沉积的纳米金颗粒没有湿到衬底上，有很小的接触面积。(3)沉积在氢暴露-(110)面上的纳米金颗粒与表面湿润良好。考虑到钛原子在表面的偏聚，较薄的金颗粒可能与钛原子结合，甚至形成合金相。(4)将这种扁平而薄的金颗粒加热后，会转变成与金红石表面接触面积较小的粗颗粒。综上所述，我们发现金红石表面和/或纳米金颗粒的结构和形貌的变化是由于无金原子表面和有金原子表面的氧化还原过程引起的。钛原子在纳米金颗粒下的偏析和保留在外围的氧原子都起到了活性作用，这与以前的说法不同。较少

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