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 on the Co3O4 (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 Co3O4 (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 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 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 3d 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.

Investigation of the effect of thermal annealing of Ni-cobaltite nanoparticles on their structure, electronic properties and performance as catalysts for the total oxidation of dimethyl ether

“…This material system was used to describe the interaction of the pure and chemically modified (Fe-doped) Co 3 O 4 (001) surfaces with water and alcohols, in good agreement with the experimental observations. [79][80][81][82][83][84][85] Vacancy stability. Oxygen vacancies play a key role in oxidation processes.…”

2-Propanol Activation on the Low Index Co3O4 Surfaces: A Comparative Study Using Molecular Dynamics Simulations

“…Their fold coordinatively unsaturated nature allows them to participate in 2-propanol a tion and decomposition. On the B-terminated (001) surface, only the topmost layer and, to a lesser exte first inner layer were involved in 2-propanol activation [18,19]. In the case of the Bnated (111) surface, 2-propanol activation is assisted by inner surface layers as illus by the charge density difference (CDD) calculated for the final equilibrium trajector ure 4).…”

“…Moreover, Co 3+ ions located in the third inner layer of the slab (orange rectangle), are also electronically involved, as it can be seen by the charge reorganization in the vicinity of these sites. On the B-terminated (001) surface, only the topmost layer and, to a lesser extent, the first inner layer were involved in 2-propanol activation [18,19]. In the case of the B-terminated (111) surface, 2-propanol activation is assisted by inner surface layers as illustrated by the charge density difference (CDD) calculated for the final equilibrium trajectory (Figure 4).…”

“…We recently used ab initio molecular dynamics (AIMD) simulations to study the role of temperature, surface structure and electrochemical environment on the oxidation process [18]. In a following study, we combined static DFT + U calculations and theoretical XANES to investigate the electronic properties of the active sites during 2-propanol oxidation to acetone on the B-termination of the Co 3 O 4 (001) surface in dry and humid conditions [19]. Recently, we studied the interaction of 2-propanol with the Co 3 O 4 (001) surface by vibrational sum frequency spectroscopy and AIMD simulations, both near ambient conditions [20].…”

A comparative DFT study of HCHO decomposition on different terminations of the Co3O4(110) surface

“…First, we can evaluate the HCHO decomposition abilities of (110)-A and (110)-B terminations, which is helpful to improve the catalytic activity of Co 3 O 4 . Second, to our knowledge, other organic probe molecules, for example 2-propanol, [34][35][36] have also been used as a probe to study the surface properties of Co 3 O 4 . Thus, the HCHO in this study combined with other organic probe molecules is expected to enlighten further investigations of the Co 3 O 4 surface properties.…”