Spill-over process of hydrogen sorption on palladized alumina, yttria and zeolite 4A

• Published in: Journal of materials science 1992-07, Vol.27 (14), p.3733-3742
• Main Author: SUSIC, M. V
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-gas interface; Surface physical chemistry
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/BF00545449

Doping of alumina, yttria and zeolite 4A with small quantities of Pd (down to 0.025%) was done. It was shown that these oxides, which do not normally absorb hydrogen, after the doping acquire a considerable capacity for H absorption. The sorption of H is occurring by the spill-over effect from metallic Pd to the oxide. The process is exothermal, taking place in two stages between 60-350 deg C. Activation energies of the first stage range from 120-167 kJ/mol exp --1 and for the second one from 20-30 kJ mol exp --1 . After cooling to room temperature in H flow, the samples are able to absorb considerable quantities of oxygen which reacts exothermally with the previously formed hydride. On next exposition to H, a vigorous reaction of it with the adsorbed O is taking place already at room temperature. Enthalpies of H absorption, -- Delta H, are of the order of 10 kJ g exp --1 , showing a tendency of increase after repeated exposures to H.