Pseudo-2-Fold Surface of the Al13Co4 Catalyst: Structure, Stability, and Hydrogen Adsorption
Résumé
A few low order approximants to decagonal quasicrystals have been shown to provide excellent activity and selectivity for the hydrogenation of alkenes and alkynes. It is the case for the Al13Co4 compound, for which the catalytic properties of the pseudo-twofold orientation have been revealed to be among the best. A combination of surface science studies, including Surface X-Ray Diffraction, and calculations based on Density Functional Theory, is used here to derive an atomistic model for the pseudo-twofold o-Al13Co4 surface, whose faceted and columnar structure is found very similar to the one of the twofold surface of the d-Al-Ni-Co quasicrystal. Facets substantially stabilize the system, with energies in the range 1.19-1.31 J/m 2 , i.e. much smaller than the ones of the pseudo-tenfold (1.49-1.68 J/m 2) and pseudo-twofold (1.66 J/m 2) surfaces. Faceting is also a main factor at the origin of the Al13Co4 catalytic performances, as illustrated by the comparison of the pseudo-tenfold, pseudotwofold and facet potential energy maps for hydrogen adsorption. This work gives insights towards the design of complex intermetallics catalysts through surface nanostructuration for optimized catalytic performances.
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