Abstract
Small-angle X-ray scattering observations on Pt/NaY catalysts, made in situ during calcination and reduction stages of processing, demonstrate the usefulness of this technique in following morphological changes. Observations show that the same platinum species (Pt0 under the preparation conditions used) is present in the early stages of calcination, carried out at relatively high heating rates, as after reduction, and that the ultimate dispersity of the metal is already reached within 0.5 h of the start of calcination. Increasing aggregation of metal particles occurs at calcination temperatures higher than 573 K, leading to average particle sizes too large to fit the supercages of the zeolite framework. With the assumption that the metal is a Maxwellian distribution of spheres, values of the distribution parameters giving the best fit to the scattering for each catalyst sample are found; from these parameters, average particle radii are calculated.
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