Surface orientation dependent interaction of cobalt (II) precursors with alpha-alumina
2021
Chizallet, Céline | Schlaup, Christian | Fonda, Emiliano | Carrier, Xavier
The performances of alumina-supported cobalt catalysts strongly depend on Co/alumina interactions, that are poorly understood. In the present work, α-alumina surfaces are used as models of polycrystalline support, to unravel their orientation dependent behavior by GI-EXAFS. The Coᴵᴵ/α-alumina interactions in the dried state are investigated, with a resolution of the parallel versus perpendicular deposit formation. DFT calculations shed light on the existence of specific grafting modes. EXAFS shows that Co(OH)₂ forms parallel to the R(11¯02), A(112¯0) and M(101¯0) surfaces, whatever the contact time (from 1 h to 6 days). However, a specific behavior of the C(0001) surface is observed. Whereas after one hour, the same parallel Co(OH)₂ is observed, at longer times it disappears while species exhibiting long then short Co-Co distances appear. The latter is assigned to epitaxial grafting of Coᴵᴵ leading to a mixed phase, that is possible parallel to the C surface due to surface symmetry.
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