Computational Investigation of CO Adsorption and Oxidation on Mn/CeO₂(111) Surface

Abstract

The interaction and mechanism for CO oxidation on the Mn/ CeO 2 (111) surface have been studied by using periodic density functional theory calculations corrected with the on-site Coulomb interaction via a Hubbard term (DFT + U). It is found that the Mn dopant facilitates oxygen vacancy formation, while the Mn adatoms may restrain oxygen vacancy formation. In addition, physisorbed CO, physisorbed CO 2 ,and chemisorbed CO (carbonite, CO 2 − ) species are observed on the Mn-doped CeO 2 (111) surface, in contrast, only physisorbed CO is found on the pure CeO 2 (111) surface. The vibrational frequency calculations as well as the calculated adsorption energies are carried to characterize these species. The Mn dopant promotes CO oxidation without any activation energy leading to O vacancy formation and CO 2 desorption. The Bader charge analysis is carried to characterize the oxidation state of Mn ions along the catalytic cycle.

Understanding the Role of Surface Oxygen in Hg Removal on Un‐Doped and Mn/Fe‐Doped CeO2(111)

“…And then Ce 0.96 Mn 0.04 O 2‐x (111) surface is established with the desorption of HgO molecule. It coincides well with the study of Hsu et al, the lattice O was activated in a great degree when CeO 2 (111) surface was doped with metal Mn, which led to the production of surface O vacancy easily. This is an essential prerequisite for this cyclic process to be completed.…”

“…Meanwhile, plenty of experimental and theoretical results showed that the introduction of the second metal could greatly improve the activity of surface O and oxidation capacity of CeO 2 . CO adsorption on un‐doped CeO 2 (111) and Mn‐doped CeO 2 (111) surfaces had been studied by using the DFT method, and the results showed that there were three adsorption modes for CO on the Mn‐doped CeO 2 (111), including physical, chemical adsorption and the oxidation state CO 2 by CO binding with the surface O, but only physical adsorption on the un‐doped CeO 2 (111) surface . In addition, the Mn‐doped increased the activity of the lattice O and the O vacancy formation energy was 0.46 eV, which was far less than un‐doped CeO 2 (111) surface (2.08 eV) .…”

A theoretical study on CO sensing mechanism of In-doped SnO2 (110) surface

“…Similar reaction mechanism was recently reported for the CO oxidation on the surfaces of metal oxides [42,43,[49][50][51][52]. For example, the bridge oxygen atom can act as an adsorption site for CO which can be oxidized to CO 2 by overcoming a barrier of 0.6 eV on the TiO 2 (110) surface [49], and this reaction is 4.2 eV exothermic.…”

“…Sorescu et al [42] found that the adsorption energies of CO on the TiO 2 (110) surface was increased with the increase of the oxygen vacancy concentrations. Hsu et al [43] reported that oxygen vacancy promotes the CO oxidation with no activation energy for the Mn-doped CeO 2 (111) surface. It also has been reported that the In-doping creates even more desired oxygen vacancies by substitution of Sn atoms [30,32], thus enhances the reaction of CO with the SnO 2 (110) surface.…”

Catalytic propane reforming mechanism over Mn-Doped CeO2 (111)

“…Density functional theory (DFT) studies have suggested that Mn can be doped into the fluorite lattice of ceria when there are oxygen vacancies present [3], and Mn-doped CeO 2 will have a high rate for oxidation of methane [4]. MnO x /CeO 2 has also been shown to oxidize volatile organic compounds [5], toluene [6], tars (C 10 H 8 ) [7], hydrocarbons with chlorine (trichlorophenol [8] and trichloroethylene [1]), and CO [9]. Though the ability of Mn-doped CeO 2 to oxidize hydrocarbons is well established, the lack of mechanistic information limits further active site optimization.…”