Calcination-Dependence of Platinum Cluster Formation in NAY Zeolite: A Xenon-129 NMR Study

Abstract

Xenon-129 NMR spectroscopy of adsorbed xenon is used to monitor the location of metal clusters and cluster precursors as a function of calcination conditions for NaY zeolite-supported platinum catalysts. Our results indicate that for the 673 K reduction conditions imposed, the formation of highly dispersed platinum clusters within the Y-zeolite matrix is best achieved by employing a calcinatoin temperature close to 673 K. Incomplete decomposition of the ion-exchanged Pt(NH 3) 4 complex during calcination at 473 K results in migration of nearly all platinum to the exterior surface of the zeolite crystallite during reduction. Calcination temperatures significantly above 673 K induce decomposition of the shielded precursor species and subsequent migration of the metal into the sodalite cavities. A substantial amount of the platinum confined within the sodalite cavities migrates back into the supercages during reduction at 673 K. The Xe NMR data are corroborated by hydrogen chemisorption and transmission electron microscopy experiments. © 1989.