Atmospheric electron

Baker pioneered direct measurements of the onset of particle mobility on substrates using controlled atmosphere electron microscopy (17). He has pointed out the close relationship between the onset of particle motion as determined in his studies and the Tammann temperature (18). It is important to establish whether melting temperature decreases monotonically with particle size as indicated by the data of Buffat and Borel (7) or is equal to the Tammann temperature as hypothesized by Baker (18). 

Controlled atmosphere electron microscopy was used to directly follow the formation of carbonaceous deposits on supported ruthenium particles during reaction with acetylene (ref. 73). Under these conditions the major type of deposit was filamentous carbon, and its growth characteristics were found to depend on the nature of the support, specimen pre-treatment conditions, and the reaction temperature. When the reaction was performed on a graphite support the filaments were produced by the... 

A combination of controlled atmosphere electron microscopy and flow reactor techniques have been used to investigate the influence of hydrogen sulfide on the catalytic activity of cobalt. Changes in the behavior of cobalt were monitored by the use of probe reactions which are sensitive to the chemical nature of the catalyst surface. These included graphite gasification in oxygen and hydrogen, and carbon deposition from decomposition of hydrocarbons. 

Approaches and Methods to Study Thermal Stability of Model-Su[yoiled Catalysts. - A number of techniques can be applied to the investigation of model-supported catalysts. They include TEM, controlled atmosphere electron microscopy (CAEM), temperature-programmed... 

Among the established instrumental methods for determining metal dispersion, electron microscopy appears to be finding increasing favour and recent advances include the application of high-resolution and controlled-atmosphere electron microscopy to supported metal catalysts (Section 3). Recently, attempts have been made to estimate crystallite size from XPS intensities EXAFS also promises a still more complete description of the... 

Instrumental techniques successfully applied to investigation of model supported catalysts include TEM, CAEM (controlled-atmosphere electron microscopy), TPD, EXAFS, AES, XPS, STM, XRD, and Mdssbauer Spectroscopy. Analytical HRTEM and same area studies have demonstrated great promise for advancing mechanistic knowledge in this area of science. 

Figure 8. Model of the transformations observed for tungsten oxide on an alumina film by controlled atmosphere electron microscopy.

Analytical (examples include single particles in the atmosphere, electron-capture detector, use of synchrotrons for aqueous systems, increased time resolution for atmospheric measurements)... 

Recently, controlled atmosphere electron microscopy (CAEM) or in situ TEM has allowed in situ observation of gas-solid reactions at a resolution of about 25 A. The principal feature of the technique is that a relatively high gas pressure is obtained at the specimen while preserving the low pressure needed for operation of the microscope. Various types of cell and differentially pumped systems have been described (164). The applications of CAEM to catalysis have been reviewed with special emphasis on carbon deposition, carbon gasification, and sintering studies (165). 

As far as the growth mechanism of CNFs is concerned, pioneering works by Lobo et al. [33] and Baker and co-workers [34] were based on two different techniques, allowing the process to be monitored continuously a microbalance reactor [33] and controlled-atmosphere electron microscopy [34]. The former technique allowed for detailed kinetic measurements, from which a mechanism was proposed that involved the detachment of metal particles from the support, carbon growing beneath these particles and pushing them away from the surface. Observations of Baker have clearly confirmed this mechanism. These early studies [33-36] mark three important steps after hydrocarbon decomposition... 

---