Radiolytic preparation of nanosized Pt particles in sodium zeolite A

Nanosized platinum metal particles in zeolite NaA have been prepared by four different methods, namely, (I) gamma-radiolysis of zeolite A sample exchanged with [Pt(NH3)(4)](2+) (II) gamma-radiolysis of precursor gel containing Pt2+ ions followed by hydrothermal crystallisation to form zeolite A, (III) hydrogen reduction of Pt2+ ions containing precursor gel followed by hydrothermal crystallisation and (IV) impregnation of zeolite A with H2PtCl6 solution followed by reduction at 200 degreesC in hydrogen flow. The size of Pt metal particles has been evaluated from X-ray line broadening and TEM and is found to be in the range of 5-15 nm for samples II, III and IV. Based on catalytic activity of these samples for hydrogenation of ethylene and cyclohexene, it is inferred that for sample I, Pt metal particles are confined to the pores of zeolite A. Unlike this, the Pt metal particles are randomly distributed in the zeolite matrix for samples II and III. For sample IV, the Pt metal particles are present over the surface of zeolite A. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.