Abstract
The performance of zeolite-supported metal catalysts is known to depend upon preparatory treatments.' Homogeneous and reproducible metal dispersion can be achieved only through careful control of calcination and reduction conditions, since migration and agglomeration of cluster precursors can occur with subsequent loss of catalytic activitya2s3 In spite of considerable the transformations undergone by metal guest species during calcination and reduction have not been established, primarily due to difficulties in characterizing chemical intermediates which exist as cluster precursors. By using the lz9Xe NMR spectroscopy technique pioneered by Fraissard and c o -w~ r k e r s 'a~n'd~ a pplied to recent advantage by us and others,I4-l6 we gain insight into the detailed chemistry of metal-zeolite catalyst preparation. We report for the first time changes in the chemical environment of Nay-supported platinum guest species by monitoring shifts in the '29Xe resonance signal induced by different chemical and thermal treatments.