Platinum-zeolites particle size effects

EXAFS is also well suited for the study of finely divided metal (or metal oxide or metal sulfide) clusters supported within the pore structure (see Chapter 6). These particles are readily observed by X-ray spectroscopy, even if they are disordered throughout the solid. Analysis can even determine the average particle size of such clusters, which is of vital importance in catalytic preparation. Typically, for example, platinum supported on zeolites (and other solid acids) is a highly effective catalyst in the reforming of hydrocarbons. 

As platinum is especially important in catalysis, strong experimental efforts have been made to characterize small Pt particles entrapped in zeolite cages, using the whole arsenal of spectroscopic, structural and chemical methods (e.g. Refs. 200, 241, 242 and references therein). However, the interpretation of experimental data often remained ambiguous because the measured values commonly reflect more than one effect as a rule, when the electronic state of an encapsulated metal species changes due to interactions with the zeolite host, so do its size and shape. Model calculations enable to separate these effects. 

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