Résumé
By using 129Xe as an n.m.r.-detectable probe it has been possible to determine quantitatively the distribution of CO molecules chemisorbed on small platinum particles (containing on average six atoms) located in the supercages of NaY zeolite. At 25 °C CO molecules are chemisorbed on the first particles encountered on entering the zeolite crystallite, with a coverage of one CO molecule per two Pt atoms. In contrast, at 300 °C one can obtain, at low coverage, a homogeneous distribution corresponding to only one CO molecule per particle.