Publications scientifiques
* (Auteur correspondant)
Autres affiliations : Christian-Albrechts-Universität zu Kiel
Dick Hartmann Douma* (Auteur correspondant)
Amir Hossein Omranpoor
Stéphane Kenmoe* (Auteur correspondant)
Alessio Lamperti
A. Debernardi
The Journal of Physical Chemistry C
We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of the active sites on the Co 3 O 4 (001) surface during 2-propanol oxidation to acetone in humid conditions. In the gas phase, the O K-edge spectra of 2-propanol and acetone, as well that of 2-propoxide considered as a reaction intermediate, present no pre-edge peaks. Upon 2-propanol adsorption at the Co site of the Co 3 O 4 (001) surface, the O K-edge spectrum presents a distinct peak preceded by a bump in the pre-edge region, both due to dipole transitions from O 1 s to 2 p states hybridized with Co 3 d empty states. The formation of 2-propoxide leads to two distinct pre-edge peaks due to the increase of 3 d empty states. A further increment of these pre-edge peaks is observed when acetone is formed and is rather ascribed to the new contributions of carbon 2 p empty states in the transitions occurring in the pre-edge region. The changes observed in the pre-edge peak along the oxidation were correlated to the electronic configuration and hybridization of the cobalt atom directly bonded to alcohol. The variation of electron densities was also monitored for all surface cobalt atoms including the ones on which molecular water and dissociated water are adsorbed. The PDOS analysis and crystal field theory showed that adsorption of 2-propanol and molecular water on the surface does not change the oxidation state of +3, while surface cobalt atoms bonded to OH groups have an oxidation state of +4. The 3 d Löwdin charges analysis shows pronounced cooperative effects between both Co sites during the last oxidation step which corresponds to the decomposition of 2-propoxide to acetone.
