Electron microscopy in catalysis

Transmission electron microscopy is one of the most often used techniques for the characterization of catalysts. Determination of particle sizes or of distributions therein has become a matter of routine, although it rests of course on the assumptions that the size of the imaged particle is truly proportional to the size of the actual particle and that the detection probability is the same for all particles, independently of their dimensions. In situ studies of catalysts are of special interest and are possible by coupling the instrument to an external reactor. After evacuation of the reactor, the catalyst can be transferred directly into the analysis position without seeing air [17-19J. Numerous applications of electron microscopy in catalysis have been described in the literature, and several excellent reviews are available [2-6],... 

Gai, P.L., and Boyes, E.D., Electron Microscopy in Heterogeneous Catalysis. Insitute of Physics Publishing, Bristol, UK, 2003. 

P.L. Gai, E.D. Boyes, Electron Microscopy in Heterogeneous Catalysis, Institute of Physics Pubhshing, Bristol and Philadelphia (2003). 

The key role of electron microscopy in the discovery of novel reaction mechanisms in selective oxidation catalysis... 

The introduction in catalysis of bimetallic formulations created an important area of application of microanalysis in transmission electron microscopy. In particular, with selective hydrogenation and postcombustion catalysts, where the metallic particle sizes are several nanometres, the STEM can be used to determine the composition particle by particle and thus confirm the success of the preparation. Figure 9.16 shows the analysis of individual particles in a bimetallic preparation. It is easy to detect the existence of genuinely bimetallic particles and others containing only platinum. It should, however, be noted that this analysis, obtained on a few nanometer sized particles, concerns only a very small quantity of the catalyst (in the present case approximately 10" g of metal ). As we have noted, it is dangerous to extrapolate only one result of this type to the solid as a whole. A statistical analysis of the response of a very large number of particles, in addition to a preliminary study of the chemical composition at different scales, can be used to confirm that this case indeed concerns two groups of particles. 

The use of transmission electron microscopy in heterogeneous catalysis centers around particle size distribution measurement, particle morphology and structural changes in the support. Consideration is given to the limitations of conventional electron microscopy and how modifications to the instrument enable one to conduct in-situ experiments and be in a position to directly observe many of the features of a catalyst as it participates in a reaction. In order to demonstrate the power of the in-situ electron microscopy technique examples are drawn from areas which impact on aspects of catalyst deactivation. In most cases this information could not have been readily obtained by any other means. Included in this paper is a synopsis of the methods available for preparing specimens of model and real catalyst systems which are suitable for examination by transmission electron microscopy. 

According to the structure and composition of materials and analysis requirements of the researcher, the following analysis techniques can be selected for the characterization of mesoporous materials XRD, TEM, adsorption-desorption (N2 or other gas), solid MAS NMR (29Si, 27Al, 13C, etc.), scanning electron microscopy (SEM), catalysis test, Fourier Transform infra-red (FT-IR), thermal analysis, UV-visible, and chemical analysis. IR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure XANES, extended X-ray absorption fine structure EXAFS and other spectral methods are commonly used to analyse metal elements such as Ti in the mesoporous material frameworks. 

The hydrogenolysis of methylcyclopentane has also been studied by Kramer and Zuegg (296). The catalysts were prepared by the evaporation of Pt and its condensation onto amorphous alumina. Particle sizes (2.5 nm) were measured by electron microscopy. In accord with Fig. 17, the nonselective production of hexane was enhanced for small particles. When additional A1203 was then deposited on top of the Pt particles, more hexane was favored. Since the Pt crystallite size was not altered, a mechanism involving catalysis by the phase boundary, Pt-Al203, was proposed (296). However, the decoration of the Pt surface by A1203 could... 

Block, J.H., Ehsasi, M., Gorodetskii, V., Karpowicz, A., and Berdau, M., Direct observation of surface mobility with microscopic techniques photoemission electron and field electron microscopy, in New Aspects of Spillover Effect in Catalysis Studies in Surface Science and Catalysis, Inui T., et al., Eds., Elsevier, Amsterdam, 1993, Vol. 77, pp. 189-194. 

Gai PL, Boyes ED, editors. Electronic microscopy in heterogeneous catalysis. London Institute of Physics Publishing 2003. 233 p. 

Gallezot P, Leclercq C. Characterization of catalysts by conventional and analytical electronic microscopy. In Imelik B, Vedrine JC, editors. Catalyst characterization, physical techniques for solid materials, fundamental and applied catalysis. Heidelberg Springer 1994. p. 509-58. 

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

The forty-eighth volume of Advances in Catalysis includes a description of a new and increasingly well understood class of catalysts (titanosilicates), a review of transmission electron microscopy and related methods applied to catalyst characterization, and summaries of the chemistry and processes of isobutane-alkene alkylation and partial oxidation and C02 reforming of methane to synthesis gas. 

Scanning Electron Microscopy and Extreme FESEM in Catalysis. 195... 

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