DISPERSION OF PLATINUM IN PT/ZSM-5 ZEOLITES

The dispersion of Pt in reduced Pt/ZSM-5 zeolites has been studied using electron microscopy and hydrogen chemisorption. Upon activation in O2 at 200°C and reduction in H2 at 400°C, 6- to 15-Å Pt agglomerates, most of which can fit in the channels and channel intersections in the bulk of the zeolite, are formed. However, they show little ability to chemisorb hydrogen (H/Pt = 0.33). Activation at 350°C prior to reduction produces mainly 20- to 25-A metal particles, most of which are presumably located on the external surface of the zeolite, and these have a higher ability for hydrogen chemisorption (H/Pt = 0.69). Upon raising the activation temperature to 450°C prior to reduction, larger metal crystallites (mainly 30-55 Å diameter) are obtained. They are also presumably located on the external surface of the zeolite and chemisorb hydrogen only to a small extent (H/Pt = 0.35). © 1992.