Ex SituTransmission Electron Microscopy: A Fixed-Bed Reactor Approach

Abstract

A fixed-bed reactor has been designed and constructed for ex situ transmission electron microscopy (TEM) studies of heterogeneous catalysts. The ex situ facility exposes a fully prepared TEM sample on a grid to actual process conditions (e.g., temperature, pressure, gas composition, etc.) by placing the grid at the exit section of a conventional fixed-bed reactor. A unique reactor design allows grid transfer into the electron microscope and back into the reactor again under a controlled (inert) environment, thus allowing time-resolved monitoring of catalyst morphology changes under realistic, well-controlled conditions. This facility stands completely independent of the TEM. Thus, no special TEM modifications are required and long-term ex situ studies do not impact microscope utilization. The utility of the facility is demonstrated via the oxidation of intermediate size ( approximately 20- approximately 80 nm) supported copper particles.

Deactivation and Regeneration of Commercial Type Fischer-Tropsch Co-Catalysts—A Mini-Review

“…They observed oxidation of a fraction of the smaller cobalt crystallites when supported on alumina or activated carbon, and recommended that careful crystallite size management is required for a commercial catalyst. Kliewer et al studied redox transformations of cobalt catalysts by TEM in terms of agglomeration of the metal, mixed-oxide formation with the support and reversible oxidation followed by reduction under mild hydrogen treatment [57]. They claim that reactor and TEM studies show that nanoscale Co crystallites can oxidize to CoO during commercially relevant FT synthesis conditions in spite of bulk thermodynamic data that suggest otherwise [58].…”

Methods of electron microscopy of biological and abiogenic structures in artificial gas atmospheres

“…The first attempts at creating electron microscopes with controlled pressure of the gas date back to the early 1960s [38], but their actualization did not take place until the creation of ESEM in 1980s, while cur rently variable pressure electron microscopes are heavily used for charge contrast mapping of biological samples [39] and similar tasks of biological visualiza tion [40], as well as for ultramicroscopic sample prep aration and processing of samples at a nanostructured level [41]. The second problem is somewhat more complicated because, if electron microscopy is con sidered in a reactor approximation [42], it is necessary to take into account the inevitable interaction of the gas being pumped into the chamber with the gaseous components of biological tissues, which is particularly relevant in the case of objects popular for electron microscopic visualization such as gas vacuoles of sin gle celled animals [43] or lung tissues [44], as well as in experiments on the study of the secondary structure of protein in gas vesicles [45] and applied test mea surements on gas permeable lenses [46]. Since numer ous myohistological studies and interdisciplinary bio molecular works are also conducted in electron micro scope chambers with a controlled composition of the gas [47,48], this statement can be extended to this field as well, and taking into account the catalytic character of interactions and enzymatic properties of myosin [49], this line of research can be interpreted as an analog of catalytic electron microscopic studies in a gas atmosphere [50].…”

Using Ex-situ TEM to Understand the Effect of Different Oxidative Environments on Small Metal Particle Morphology

“…The fines were dusted onto a 200 mesh, holey-alumina-coated TEM grid. The grid was transferred into a specially designed ex-situ reactor where it was treated and then moved via an inert transfer protocol into a Philips CM200F for examination [7]. Metal particles were imaged in the bright field (BF) TEM mode at an accelerating voltage of 200 kV, and areas of interest were "mapped" so that the same metal particles could be re-examined subsequent to each reactor treatment.…”