A NaY + CaY or NaY + Pt/NaY powder zeolite mixture was soaked with liquid octamethylcyclotetrasiloxane (OMTS) in situ under an atmosphere of xenon. The OMTS coating on the zeolite crystallites blocked the intercrystal diffusion of xenon very effectively at room temperature; while it did not affect the interior of the zeolite matrix. Xe-129 NMR spectra of the two mixtures complexed with OMTS showed two distinct signals corresponding to the different components in the respective mixtures. The application of the Xe-129 NMR spectroscopic technique using OMTS to Pt/NaY and Ni/NaY samples distinguished the chemical shifts due to the xenon interaction with the metal clusters located inside the zeolite matrix from those on the external surface.