Probing the local environment of active sites during 2-propanol oxidation to acetone on the Co3O4 (001) surface: insights from first principles O K-edge XANES spectroscopy

Abstract

We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of the active sites during 2-propanol oxidation to acetone on the Co3O4 (001) surface 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 reaction intermediate, present no pre-edge peaks. Upon 2-propanol adsorption at the Co site of Co3O4 (001) surface, the O K-edge spectrum presents a distinct peak preceded by a bumb in the pre-edge region, both due to dipole transitions from O 1s to 2p states hybridized with Co 3d empty states. The formation of 2- propoxide leads to two distinct pre-edge peaks due to the increase of 3d 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 2p 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 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 oxi- dation state of +4. The 3d Loewdin 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.

Co3O4 (111) surfaces in contact with water: Molecular dynamics study of the surface chemistry and structure at room temperature

“…9,10 In such processes, water can play a controversial role as it could destabilize [11][12] or stabilize co-adsorbed species. [13][14][15] However, compared to the (001) and (101) that were studied at different coverage regimes, [16][17][18][19] the interaction of water with the Co3O4 (111) has not been studied to an extend that would allow a fundamental understanding of its role on the catalytic activity.…”

2-Propanol Interacting with Co3O4(001):A combined AIMD and vSFS study

“…[7][8][9] In addition, the various electronic, magnetic and redox properties of Co 3 O 4 have also stimulated several studies in recent years. [10][11][12][13][14][15] Falk et al 1 studied the oxidation of 2-propanol over Co 1+x Fe 2-x O 4 spinel oxides in contact with both the liquid and the gas phase. They reported that increasing the Co content will increase the catalytic activity of the samples for 2-propanol oxidation, which shows that the iron-free Co 3 O 4 samples have the highest catalytic activity.…”