Hydrogen adsorption and spill-over effects on H–Y and Pd-containing Y zeolites: An experimental and theoretical investigation

The adsorption of hydrogen on H–Y and Pd(0)–H–Y zeolites was investigated by IR (in the 300–20 K temperature range) and EXAFS spectroscopies and the energy barriers for diffusion of hydrogen in the internal voids of the faujasite structure evaluated by ab initio calculations. On H–Y, H2 is adsorbed at 20 K inside the super-cages giving rise to 1:1 –OH⋯H2 hydrogen bonded complexes with the Brønsted acid groups, as well as less specific interaction with the cage walls. Due to the high energy barrier for crossing the framework hexagonal apertures, H2 cannot enter the sodalite-cages. On Pd(0) containing zeolites, characterized as far the dispersion of the metal is concerned by TEM, EXAFS and IR spectroscopy of adsorbed CO, hydrogen is adsorbed in atomic form to give a metal-hydride phase; subsequent spill-over effects allow confinement of hydrogen also in the small sodalite-cages, as demonstrated by H/D isotopic substitution experiments.