Abstract
Abstract Size and location of Pt particles in Y zeolites largely depend on the conditions of calcination following ion exchange. Besides destroying NH 3 ligands, calcination promotes migration of Pt ions from supercages to sodalite cages. The calcination temperature thus determines whether all, some, or none of the Pt ions remain in the supercages. In the first case, subsequent reduction results in small Pt clusters in supercages. Large Pt particles are, however, formed at the external surface, if all Pt ions were located in sodalite cages. If Pt ions are present in comparable quantities in both types of cages, those located in the supercages are reduced at low temperature and act as nucleation sites for the Pt atoms leaving the sodalite cages at higher temperature. By filling sodalite cages with auxiliary ions of other transition elements, the migration of Pt ions such cages can be suppressed; and a higher platinum dispersion is obtained after reduction.
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