Intrazeolite Pd clusters: particle location

A chemical vapour deposition (CVD) procedure has been adopted for the preparation of Pd/NaY, resulting in a high dispersion of the metal phase, characterised by a bimodal distribution of particle size. The most abundant particles (80%) are about 25 Å in size, corresponding to almost twice the dimension of the zeolitic supercages. To identify their location inside or outside the zeolite matrix, the IR spectra of adsorbed CO, obtained before and after admission of NH₃, have been compared. The results obtained are in sharp contrast with those for a Pd/SiO₂ system, where Pd particles of comparable size are exclusively located on the external surface of the carrier. These differences support the conclusion that Pd particles in Pd/NaY are indeed located in the zeolitic cavities.