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Chemische Prozesse und Phasenübergänge Poster: Mi., 14:00–16:30 M-P175
The influence of subsurface carbon on the selectivity in the hydrogenation
reaction of 1-pentyne over Pd catalysts
Axel Knop-Gericke 1 , Detre Teschner 1 , Michael Hävecker 1 , Spiros
Zafeiratos 1 , Hermann Sauer 1 , Elaine Vass 1 , Robert Schlögl 1 , Arran S.
Canning 2 , David Jackson 2 , James McGregor 3
1 Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin – 2 WestCHEM, Department
of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, UK –
3 University of Cambridge, Department of Chemical Engineering, New Museums Site,
Pembroke Street, Cambridge CB2 RA, UK
The hydrogenation of 1-pentyne over various palladium catalysts was studies under different
conditions. X-ray Photoelectron Spectroscopy (XPS) measurements performed
at the synchrotron radiation facility BESSY in Berlin at 0.9 mbar in a mixed atmosphere
of hydrogen and 1-pentyne show significant amounts of subsurface carbon and a
Pd-C surface phase builds up in the early stage of the reaction in the regime of selective
hydrogenation. These species inhibit the emergence of bulk-dissolved hydrogen to the
surface, which is reactive, but unselective. Carbon laydown was also observed by Tapered
Element Oscillating Microbalance (TEOM) and by catalytic pulse experiments
with greater laydown occurring in the selective regime. The effect of carbon dissolution
in the crystal lattice near the surface was evidence by High-Resolution Transmission
Electron Microscopy (HRTEM). In alkyne hydrogenation the active phase of palladium
catalysts is a Pd-C surface phase in the regime of selective hydrogenation. As
self-hydrogenation (hydrogen from dissociated 1-pentyne) was shown to be unselective
as well, only surface hydrogen from the gas phase is available to generate the alkene.
A model of the palladium surface during 1-pentyne hydrogenation is suggested.
The contribution shows, that the application of synchrotron radiation to perform
X-ray photoelectron spectroscopy under reaction conditions, is a very powerful tool
for the characterization of heterogeneous catalytic processes especially in combination
with other methods.
Fig. 1: Model of the palladium surface during 1pentyne
hydrogenation