Mechanism of the catalytic oxidation of CO with O2 on an Mo catalyst supported on silica and on bulk MoO3

Iizuka, Yasuo; Sanada, Masakazu; Tsunetoshi, Junji; Furukawa, Junichi; Kumao, A.; Arai, Shigeyoshi; Tomishige, Keiichi; Iwasawa, Yasuhiro

doi:10.1039/ft9969201249

Cited by 7 publications

(9 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The molybdenum–oxygen bond lengths calculated for the proposed models of the most stable dioxo Mo(VI) species on silica under dehydrated conditions are compared in Table with the reported extended X-ray absorption fine structure (EXAFS) data for molybdena–silica systems. ,, Taking into account some discrepancy of the experimental values and previously reported , slight overestimation of the predicted MoO bond lengths using this level of theory, very good agreement between the theoretical and experimental parameters is obtained.…”

Section: Resultsmentioning

confidence: 71%

Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective

2020

View full text Add to dashboard Cite

Although silica-supported molybdenum and tungsten oxide systems are widely used in catalysis, the nature of the surface metal oxide species is still not fully recognized. In this work, comprehensive periodic and cluster density functional theory (DFT) studies of the isolated Mo(VI) and W(VI) oxide species on dehydrated amorphous silica have been performed to give insight into their heterogeneity. It is shown that the relative stabilities of the metal oxide species strongly depend on their location that influences their geometry and the strain of the dehydrated silica surface. The favorable located monooxo W(VI) species are clearly more stable than the dioxo W(VI) species, whereas no strong thermodynamic preference is predicted in the case of the Mo(VI) species. The relative stability of the monoxo species increases in the order: Cr < Mo < W. However, due to geometrical constraints on the silica surface, formation of the tetragrafted monooxo species is hampered, compared to the digrafted dioxo species and the latter are expected to be in majority. The monografted hydroxy dioxo Mo(VI) species are unstable. Based on the vibrational frequency analysis, some details regarding the structure of the experimentally observed dioxo species in the MoO x /SiO2 catalyst are proposed, while the results for the WO x /SiO2 system are somewhat ambiguous.

show abstract

Section: Resultsmentioning

confidence: 71%

Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective

2020

View full text Add to dashboard Cite

show abstract

“…Mo(VI) oxide species on silica can be reduced to Mo(IV) species in the presence of H 2 , or CO. , In Table , the energies at T = 0 K and Gibbs free energies at T = 873 K for the reduction of monooxo and dioxo Mo(VI) species by H 2 are listed. If CO is taken as the reducing agent, the calculated Δ E and Δ G 873 values are lower by 88 and 67 kJ·mol –1 , respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In Table , the molybdenum–oxygen bond lengths calculated for the dioxo Mo(VI) species on silica are presented together with the corresponding experimental EXAFS data − available for the molybdena–silica system. The agreement between the theory and experiment is generally very good.…”

Section: Resultsmentioning

confidence: 99%

“… a PW91/SVP:HF/LANL2MB calculations for the series a – c and f ; PW91/SVP calculations for other models. b Ref . c Ref . d Ref . …”

Section: Resultsmentioning

confidence: 99%

“…Understanding the catalyst structure at the atomic level is extremely important for the investigations of the catalytic reaction mechanisms and necessary in effectively designing new catalysts. The structure of the monomeric molybdenum oxide species on silica is still a subject under debate, despite a number of studies using various spectroscopic techniques for the characterization of the molybdena–silica system. − ,− Moreover, dehydroxylation of the silica surface, dependent on the temperature, significantly changes its structure, , hence influencing the geometry and properties of the surface molybdenum species …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Structure of Isolated Molybdenum(VI) and Molybdenum(IV) Oxide Species on Silica: Periodic and Cluster DFT Studies

Handzlik

Ogonowski

2012

J. Phys. Chem. C

View full text Add to dashboard Cite

The structure of monomeric molybdenum oxide species on silica is still a subject under debate. In this work, a large number of advanced silica models are used to study molybdena−silica system with density functional theory. The calculated relative energies of the monooxo and dioxo Mo(VI) species depend on the location of the Mo center on the surface and on the structure of the model. Periodic and cluster calculations employing comparable models of silica give similar results. It is shown that the monooxo Mo(VI) species can be more stable than the dioxo species under dehydrated conditions, provided that the local structure of silica enables preferable 4-fold bonding to the surface. As most locations are favorable for the 2-fold bonded dioxo Mo(VI) species, they should be dominant in the molybdena−silica system, whereas the monooxo Mo(VI) species are predicted to be in minority. The calculated frequencies of the MoO stretching mode for the monooxo Mo(VI) species are generally higher than the frequencies of the symmetric OMoO stretch for the dioxo species, corresponding to the strongest band observed experimentally. The relative energies of the reduced Mo(IV) species on silica are close to the relative energies of the corresponding Mo(VI) precursors.

show abstract

The role of exposed silver in CO oxidation over MgO(0 0 1)/Ag(0 0 1) thin films

et al. 2015

View full text Add to dashboard Cite

The reactivity of MgO(001) films deposited on Ag(001) and Mo(001) in CO oxidation as a function of oxide film thickness was investigated experimentally at ambient pressure reaction conditions. MgO films grown on Mo(001) were found to be inactive in CO oxidation, whereas activity enhancement with decreasing oxide film thickness was observed for MgO(001)/Ag(001). In-situ infrared and post-reaction X-ray photoemission data showed that ultra-thin MgO films interact much more strongly with the reactants and residual water than bulk-like MgO. Poisoning of the MgO surfaces by the resultant accumulation of carbonate and hydroxyl species is suggested to inhibit the reactivity in CO oxidation. Detailed investigations of the surface structure of MgO(001)/Ag(001) films indicate that silver adislands on Ag(001), which are formed during MgO growth, are responsible for the enhancement of CO oxidation activity over ultrathin MgO(001)/Ag(001) films.

show abstract

Mechanism of the catalytic oxidation of CO with O2 on an Mo catalyst supported on silica and on bulk MoO3

Cited by 7 publications

References 15 publications

Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective

Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective

Structure of Isolated Molybdenum(VI) and Molybdenum(IV) Oxide Species on Silica: Periodic and Cluster DFT Studies

The role of exposed silver in CO oxidation over MgO(0 0 1)/Ag(0 0 1) thin films

Contact Info

Product

Resources

About