Observation of dynamic structure during hydrogenation reaction for Pd nanoparticles by using real-time-resolved X-ray absorption fine structure spectroscopy

Matsumura, Daiju   ; Okajima, Yuka*; Nishihata, Yasuo; Mizuki, Junichiro

Palladium nanoparticles show different hydrogen absorption and desorption properties from those of bulk Pd. We have developed the real-time-resolved X-ray absorption fine structure (XAFS) spectroscopy observation system with the dispersive optics in order to understand the dynamic structural change of the Pd nanoparticles during hydrogen absorption and desorption reactions. The positive peak of the Debye-Waller factor is only observed during the interatomic distance increases due to the hydrogenation reaction. This may not be consistent with the result that the limiting-rate process of the reaction is the surface dissociative adsorption of the hydrogen molecule, not the penetration of the hydrogen atoms inside of the Pd nanoparticles. We want to state that the hydrogen atoms move very quickly with making the distortion of Pd local bonds at the middle stage of the hydrogenation reaction.