Atomic resolution ETEM

VIII.B.2. Atomic-Resolution ETEM of Butane Oxidation. 203... 

Fig. 14. Schematic of the basic geometry of the aperture system and objective lens pole pieces incorporating radial holes for differential pumping system in the novel atomic resolution-ETEM design of Gai and Boyes (85-90) to probe catalysis at the atomic level.

Fig. 15. (a) Novel atomic resolution-ETEM (87) and (b) schematic of various components for imaging, chemical analysis and diffraction under catalyst operating conditions. 

The design of in situ atomic-resolution environmental cell TEM under controlled reaction conditions pioneered by Gai and Boyes (87,89) has been adopted by commercial TEM manufacturers, and latter versions of this in situ instrument have been installed in a number of laboratories. In situ atomic resolution-ETEM data demonstrated by Gai et al. (85-90) have now been reproduced by researchers in laboratories using commercial instruments examples include investigations of promoted ruthenium and copper catalysts in various gas environments (93) and detailed investigations of Ziegler-Natta catalysts (94). 

Fig. 20. (a) Active sites observed by in situ atomic-resolution ETEM structural modification of VPO in n-butane along (201) indicates the presence of in-plane anion vacancies (active sites in the butane oxidation) between vanadyl octahedra and phosphate tetrahedra. (b) Projection of (010) VPO (top) and generation of anion vacancies along (201) in n-butane. V and P are denoted. Bottom model of novel glide shear mechanism for butane oxidation catalysis the atom arrowed (e.g., front layer) moves to the vacant site leading to the structure shown at the bottom. 

Recent advances in in situ atomic-resolution ETEM for probing gas-catalyst reactions at the atomic level... 

Dynamic atomic-resolution ETEM and diffraction studies provide fundamental insights into the catalyst precursor transformation mechanism. The studies reveal that the temperature regimes are critical to the formation of active catalysts. They show that the nature of the VHPO -> VPO transformation is topotac-tic. Topotaxy is defined as the conversion of a single crystal to a pseudomorph... 

Strong metal-support interactions (SMSI) and electronic structures In situ atomic resolution ETEM... 

Figure 5.13. In situ atomic-resolution ETEM image of Pt/titania catalyst (a) finely dispersed Pt particles (b) in situ real-time dynamic activation in hydrogen imaged at 300 C. The 0.23 nm (111) atomic lattice spacings are clearly resolved in the Pt metal particle, P and (c) the same particle imaged at 450 C, also in H2. SMSI deactivation with a growth of a Ti-oxide overlayer (C), and the development of nanoscale single-crystal clusters of Pt, with atomic resolution (arrowed). (After Gai 1998.)...

Figure 5.27. Nanocatalysts of Ru/Ti02 (a) HR LVSEM image iUustrating the uniform distribution of Ru (arrowed) on the support surface (b) atomic structure of Ru/Ti02 in atomic-resolution ETEM at room temperature. The Ru is in single-crystal clusters in (001) (Ru is hexagonal a = 0.27 nm, c = 0.428 nm) and titania exhibits primarily (010) and (110). (After Gai et al 2000.)...

---