Chemical vapor deposition of zinc in zeolite HY

Zinc metal vapor was deposited in the pores of zeolite HY and reacted with the protons to yield Zn2+ ions at extraframework positions. Samples with various concentrations of surplus nonoxidized zinc were prepared by applying appropriate heating procedures in vacuo. The obtained samples were investigated with thermodynamic and spectroscopic techniques, i.e., measurements of adsorption isotherms of carbon monoxide and xenon, and of Xe-129 NMR chemical shifts of the encaged xenon atoms. The whole body of experimental data can consistently and quantitatively be interpreted on the basis of an approach that considers localized adsorption of both CO and Xe at Zn2+ cation sites and nonlocalized adsorption on the remainder of the surface of the pore walls. It is found that the surplus zinc metal atoms are inhomogeneously distributed over the sample volume and form low-nuclearity cations, most probably Zn-2(2+). It is shown that these clusters become unstable at temperatures higher than 450 degrees C, leading to removal of zinc metal atoms from the cages.