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

本研究利用高分辨透射电子显微镜对金-金红石催化剂进行了观察，以明确其催化CO气体氧化的活性位。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。另一种可能的活化位点是纳米金颗粒的表面，金和钛原子在表面形成特定的轨道，使表面具有活性。我们观察了金红石晶体在加热、氧暴露和/或氢暴露等过程后的表面结构。此外，我们还研究了纳米金颗粒和金红石晶体在上述过程前后的形貌和界面结构。通过这样的调查，我们发现了以下几点。（1）金红石晶体的晶面结构因在氧气或氢气中加热的不同而不同。 ...更多信息 n气体。氧气使空气劈裂法制备的金红石晶体表面的（211）和（100）晶面膨胀。氢气使（110）面膨胀，（211）和（100）面收缩。氢气似乎使金红石表面缺氧，因此暴露后的表面因钛原子的偏析而粗糙。随后在氢预暴露表面上暴露氧气，表面变得更光滑以恢复其化学计量。（2）详细研究了纳米金颗粒在金红石（110）表面的吸附。为了在氧暴露后制备（110）面，我们将金红石表面暴露于1200 - 1300℃的氢气中，随后暴露于700 - 900℃的氧气中。沉积在这种氧暴露的（110）面上的纳米金颗粒不润湿衬底，具有小的接触面积。（3）在氢暴露的（110）面上沉积的纳米金颗粒与表面润湿良好。考虑到钛原子在表面的偏聚，薄的金颗粒应该与钛原子结合，甚至形成合金相。（4）在加热这样的扁平且薄的金颗粒之后，它们转变成与金红石表面具有较小接触面积的厚颗粒。综上所述，我们发现金红石表面和纳米金颗粒的结构和形貌变化是由无金原子表面和有金原子表面的氧化和还原过程引起的。钛原子在纳米金颗粒下的偏聚和留在外围的氧原子都起着积极的作用，与以前的建议不同。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