Preparation of highly dispersed Pt particles in zeolite Y with a narrow particle size distribution: Characterization by hydrogen chemisorption, TEM, EXAFS spectroscopy, and particle modeling

Research on metal-support interaction calls for highly dispersed metal part icles inside the zeolite with a narrow particle size distribution. Pt parti cles thus dispersed in zeolite Y are obtained in this work using both ion e xchange and dry impregnation techniques. For both preparation techniques a very low heating rate during calcination turns out to be essential. This lo w heating rate of 0.2 degreesC/min leads to particles with an EXAFS Pt-Pt c oordination number of 56, i.e., particles of 13-20 atoms, i.e., smaller tha n 1.1 min. A rate of 1 degreesC/min as used in the literature already leads to a bimodal particle size distribution. About 5 wt% large particles of 4- 9 nm is (partially) occluded in the zeolite. Ninety-five weight percent of the Pt particles have an average size of 1-1.2 nm. The necessity to use a v ery low heating rate is explained by the slow desorption of water and ammon ia from the microporous zeolite in combination with the stabilization of mo bile Pt species by the cavity walls of the zeolite. The particle size distr ibution reported could be obtained only by combining the results of hydroge n chemisorption, TEM, EXAFS, and modeling of Pt particles. (C) 2001 Academi c Press.