Intrazeolite Pd clusters: particle location

A chemical vapour deposition (CVD) procedure has been adopted for the prepa ration of Pd/NaY, resulting in a high dispersion of the metal phase, charac terised by a bimodal distribution of particle size. The most abundant parti cles (80%) are about 25 Angstrom 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 i n sharp contrast with those for a Pd/SiO2 system, where Pd particles of com parable 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.