Reversible sorption of hydrogen by colloidal palladium in aqueous solutions

Colloidal palladium was prepared by gamma-irradiation or by H-2 reduction of Pd(NH3)(4)Cl-2 in aqueous solutions containing sodium polyacrylate as a stabilizer. The sols contain spherical particles 2-4 nm in diameter. Their optical spectra contain a band. at 230 nm (epsilon = 6.1 . 10(3) L mol(-1) cm(-1)) smoothly descending toward the visible range. The sols reversibly absorb chemically from 0.35 to 0.15 g-mol of H-2 per g-atom of Pd. The spectra of ultrafine metal particles saturated with molecular hydrogen exhibit an absorption band at 265 nm (epsilon = 4.5 . 10(3) L mol-L cm(-1)). One-electron reduction of methylviologen by hydrogen is catalyzed by the colloidal palladium prepared.