SIPS 2018

DETAILLED PROGRAM OVERVIEW

Controlling Hydrogen Absorption and Release Kinetics of Palladium Through Surface Structural Modifications
Shohei Ogura¹; Koichi Kato¹; Katsuyuki Fukutani¹; Ohno Satoshi¹; Markus Wilde¹;
¹INSTITUTE OF INDUSTRIAL SCIENCE, THE UNIVERSITY OF TOKYO, Tokyo, Japan;
PAPER: 391/SISAM/Invited (Oral)
SCHEDULED: 16:20/Mon./Copacabana A (150/1st)

ABSTRACT:
The reversible ingress of gas phase H2 into the interior of hydrogen (H)-absorbing metals is widely utilized in metal hydride storage and H2 purification. On reactive hydride-forming metals, thin palladium (Pd) surface layers promote barrier-free H2 dissociation and protection from oxidation. The kinetics of H2 absorption are of particular interest to industrial Pd-catalyzed olefin hydrogenation (fuel reforming and organic synthesis), for which Pd-dissolved H has been identified as the essential reactive ingredient that drives the H2 addition to the olefinic C=C double bond [1]. The H2 transportation mechanism between the gas phase and the metal interior, however, has not been understood very well at the atomic level until recently. It is therefore explained here how we revealed the microscopic H2 absorption process at structurally well-defined Pd single crystal surfaces through our unique combination of H depth profiling with 15N nuclear reaction analysis [2] and thermal desorption spectroscopy with isotope-labeled (H, D) surface hydrogen. We thereby demonstrate that the H2 transfer into the Pd is highly sensitive to the surface atomic structure [3]. Based on this insight into the H2 absorption mechanism, it is shown how the structure-sensitivity can be exploited by means of deliberate surface structural modifications to control, e.g., the desorption dynamics of Pd-dissolved hydrogen in a wide range of temperatures (160-375 K) [4]. Photoelectron spectroscopy and density functional calculations will further demonstrate that a modification of the surface electronic properties by surface-alloying with gold can even accelerate the H2 absorption 30-fold compared to pure Pd [5].

References:
[1] M. Wilde, K. Fukutani, W. Ludwig, B. Brandt, J.H. Fischer, S. Schauermann, H.J. Freund, Angew. Chem. Int. Ed. 47 (2008) 9289-9293.
[2] M. Wilde, K. Fukutani, Surf. Sci. Rep. 69 (2014) 196-295.
[3] S. Ohno, M. Wilde, K. Fukutani, J. Chem. Phys. 140 (2014) 134705.
[4] S. Ohno, M. Wilde, K. Fukutani, J. Phys. Chem. C 119 (2015) 11732-11738.
[5] K. Namba, S. Ogura, S. Ohno, W. Di, K. Kato, M. Wilde, I. Pletikosia P. Pervan, M. Milun, K. Fukutani, Proc. Nat. Acad. Sci. (2018) DOI: 10.1073/pnas.1800412115.