Catalysis with liquid metal alloys
C. Papp, Erlangen
Physikalische Chemie 2, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, Erlangen, Germany
Binary mixtures of Ga with low transition metal concentrations, supported on porous silica, were shown to be stable and selective alkane dehydrogenation catalysts, outperforming commercial catalysts. These systems are termed supported catalytically active liquid metal solutions (SCALMS). The beneficial effects of diluting the active transition metal in Ga are attributed to the fact that the catalyst is in the liquid phase during reaction. This leads to higher activity and selectivity via the modification of the surface active sites given by the liquid phase, and a lower sensitivity to coking.
Herein, we present photoelectron spectroscopy studies of Pd-Ga and Pt-Ga alloys with various stoichiometries below 10 at.% of Pd (Pt) in Ga as model systems for catalytically active, supported liquid catalysts. At high temperatures, the solution is in its liquid state, and shows a depletion of Pd from the surface and an enrichment in the subsurface layers.  Upon lowering the temperature, we observe a change in concentration, due to the formation of solid intermetallics, which leads to the depletion of the catalytically active transition metal from the liquid phase. Complementary data on the Pt-Ga system will be presented and compared to the results obtained for the Pd-Ga alloy. We further discuss the behavior during oxidation of the liquid metallic catalysts. 
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