Abstract
Scanning transmission electron microscopy and microdiffraction techniques have been used to study the structures of Pt/Y-zeolite catalysts. The Pt was highly dispersed in two forms of Y-zeolites, i.e. NaY and USY, and reduced at various temperatures in H 2. The size of the Pt particles ranges from a few ångström up to ∼ 30 Å. High-resolution scanning transmission electron microscope images of the zeolite structure were obtained on a dedicated VG HB-5 STEM microscope. High-angle annular dark-field imaging has proven to be much more efficient than bright-field imaging in the detection of small Pt clusters dispersed within the zeolite framework. Electron microdiffraction patterns from small Pt particles show that they were single crystals. It was found that the use of a small electron beam (10–15 Å) could cause the small Pt particles to change their orientations very rapidly. Preliminary results showed no structure correlation between the Pt particles and the zeolite supports.
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