Studies of supported metal catalysts using high resolution secondary electron imaging in a STEM

Abstract

An additional technique for use in the characterization of catalysts by electron microscopy is presented. High resolution secondary electron images obtained in a VG HB501 scanning transmission electron microscope have been used to study the surface topography of catalysts consisting of small metal particles on high surface area carbon supports. Surface features down to nanometre dimensions can be seen, allowing the examination of micropores in the support as well as larger pore structures. The results are compared with pore size distributions determined by gas adsorption methods, and are shown to yield valuable additional information. In addition, the method in principle allows examination of the locations of small metal catalyst particles on the support.

Effects of a forming process on the properties and structure of RANEY®-Ni catalysts for the hydrogenation of 1,4-butenediol

“…The corresponding hysteresis loops are type H3, and the morphology may be a sheet structure. 24 Fig. 3(a) depicts the N 2 adsorption-desorption isotherms of the Ni-Al alloys.…”

Contrast of Highly Dispersed Metal Nanoparticles in High-resolution Secondary Electron and Backscattered Electron Images of Supported Metal Catalysts

“…High-resolution SE imaging of heterogeneous catalyst samples was first demonstrated with 100 keV electrons in the STEM (Imeson, 1987;Liu andCowley, 1987, 1990a). The increased emission of secondary electrons from small, heavy-element particles is partially attributed to the local increase in the stopping power of high-energy electrons.…”

“…Several factors can contribute to the visibility of heavy-element metal particles supported on low atomic-number (Z) materials. At high electron energies, as in STEM, the increased stopping power in a small particle of high-Z material can result in emitting more secondary electrons, thus giving a bright material contrast (Imeson 1987;Liu andCowley, 1987, 1990a;Darji and Howie, 1997). However, if a small metal particle is embedded inside the support, the contrast of the particle may depend on the size of the particle, the energy of the incident electrons, and the distance between the particle and electron entrance surface of the support.…”

SEM—past, present and future

“…Cowley, 1982;Milne, 1987) with the advantage that the reflected electrons do not have to be focused and also EELS and microdiffraction analysis can be performed (Howie & Milne, 1985). Surface imaging of small particles has also been done in the STEM, for example high resolution (1 nm) secondary electron images of catalyst particles (Imeson, 1987).…”