The surfaces of platinum clusters in the supercages of NaY zeolite have been studied by ${}^{129}\mathrm{Xe}$ NMR over the temperature range 80–293 K. The sensitivity of this weakly perturbing technique makes it possible to reveal the heterogeneity of the electronic structure of the particle surface. The temperature dependence of the ${}^{129}\mathrm{Xe}$ spin-lattice relaxation indicates that the surface sites with the highest adsorption energy possess metallic character.

• Received 17 November 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.3277