Application of129Xe NMR spectroscopy and EXAFS to probe the formation of a bimetallic cluster in zeolite Y

Palladium was supported on CaY zeolite by ion exchange of Pd(NH₃) ₄ ²⁺ into CaY zeolite, calcination in O₂ and subsequent reduction with H₂. Platinum and silver were added to this Pd/CaY zeolite by ion exchange of Pt(NH₃) ₄ ²⁺ and Ag⁺, respectively, and subsequent reduction with Hg. Extended X-ray absorption fine structure of these metals indicates that the successive metal-loading treatments lead first to the formation of a 1-nm Pd cluster inside the supercage of CaY zeolite and to the subsequent formation of bimetallic clusters through incorporation of Pt and Ag atoms into the small Pd cluster. The line width and chemical shift of¹²⁹Xe NMR spectrum of xenon gas adsorbed on the zeolite show dramatic changes during the metal clustering procedure, which indicates that¹²⁹Xe NMR spectroscopy can be used to probe the formation of bimetallic clusters.