Intrinsic Catalytic Structure of Gold Nanoparticles Supported on TiO₂

Abstract

Obwohl TiO2 unter Elektronenbeschuss empfindlich ist, konnte die Struktur von Au/TiO2‐Katalysatoren transmissionselektronenmikroskopisch untersucht werden. Unter Reaktionsbedingungen (CO/Luft, 100 Pa) sind die {111}‐ und {100}‐Hauptflächen der Goldnanopartikel exponiert, und die Partikel bilden eine polygonale Grenzfläche mit dem TiO2‐Träger, die durch scharfe Kanten parallel zu den 〈110〉‐Richtungen abgegrenzt wird.

Environmental transmission electron microscopy for catalyst materials using a spherical aberration corrector

“…A quantitative analysis of atomic resolution Cscorrected ETEM images can lead to derivation of the intrinsic or native structure of supported metal nanoparticulate catalysts in reaction conditions. By accumulating substantial ETEM data as a function of electron current density and electron dose, we have shown the reversible change in the structures of even the fragile Au/TiO 2 catalyst in different gas environments employing ETEM [72]. Suffice to say, a weaker electron current density and shorter observation time, or smaller electron dose is strongly needed.…”

“…More importantly, ETEM analysis has shown that this change is reversible in gas environments [71,72]. Although a change in morphology is induced with the aid of electron irradiation, changes did not occur within experimental accuracy for gold nanoparticles that were not supported on a relevant support and thus did not have catalytic activity [71].…”

“…For example, the adsorption and reaction sites of gases, especially the activation sites in which oxygen molecules dissociate or are activated even below room temperature, were not determined. Details on the Au/CeO 2 and Au/TiO 2 catalyst that we examined here were previously described in terms of catalyst chemistry by Haruta and colleagues [58,72]. It is noteworthy that Au nanoparticulate catalysts exhibit their activity over a wide range of gas pressure below atmosphere pressure.…”

“…Therefore, to confirm that a supported nanoparticle in a viewing screen of ETEM is responsible for catalytic activity, statistical analysis combined with numerical image analysis of ETEM data is mandatory before interpreting atomic resolution ETEM images. Our quantification methodology [71,72] showed how the majority of nanoparticles behave in various gas environments. Following that result, we have further ensured the reproducibility of observation on nanoparticles under atomic-resolution ETEM observation.…”

“…This is particularly true for crystalline TiO 2 , which is widely used in various applications and is known to be fragile under electron irradiation. Electron energy-loss spectroscopy (EELS) is useful for evaluating the electron irradiation effect involving point defects [72]. A quantitative analysis of atomic resolution Cscorrected ETEM images can lead to derivation of the intrinsic or native structure of supported metal nanoparticulate catalysts in reaction conditions.…”