Monitoring Silica Supported Molybdenum Oxide Catalysts at Work: A Raman Spectroscopic Study

Thielemann, Jörg P.; Heß, Christian

doi:10.1002/cphc.201200648

Cited by 22 publications

(23 citation statements)

References 46 publications

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“…25 Other authors have found an increase of monoxo/dioxo ratio in the Raman spectra of a MoO x /SiO 2 catalyst during propylene oxidation reaction. 26 Moreover, thanks to an operando Raman/IR investigation of methanol oxidation by Mo/Al 2 O 3 , further supported by a model TPR and H 2 /D 2 isotopic exchange, the existence of reduced Mo−O−H group on surface of catalyst after reduction was attested. 20 Furthermore, the authors have detected the presence of Mo V probed by in situ EPR spectroscopy after having subjected the same catalyst to a CH 3 OH/He flow.…”

Section: ■ Introductionmentioning

confidence: 89%

Investigation of the Reducibility of Supported Oxomolybdate Species for Mapping of Active Centers of Partial Oxidation Reaction: In Situ Mo K-Edge XAS and DFT Study

Souza

Berrier

et al. 2019

J. Phys. Chem. C

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We have investigated the molecular and electronic structure of a TiO 2supported oxomolybdate phase upon reduction under methanol or dihydrogen atmosphere. In situ Mo K-edge X-ray absorption spectroscopy, supported by density functional theory (DFT) calculations and ab initio X-ray absorption spectroscopy (XAS) spectra simulation showed that the reducibility of supported molybdate species is closely related to the geometric environment of Mo atoms. Indeed, Mo atoms not involved in terminal oxo sites are easily reducible whereas Mo dioxo species are not under the conditions we have applied. Between those extreme cases, Mo atoms involved in monooxo terminal sites exhibit intermediate reducibility, which varies according to their local environment and their interaction with the support. Spin density calculations showed that under CH 3 OH flow, the surface of the catalyst is partially reduced. The structure of the reduced phase after reaction with methanol was compared to that afforded after reduction by dihydrogen. Our results show that the reduction under H 2 flow does not increase the number of reduced Mo atoms but causes a higher spin density per Mo atom. On the basis of the individual mapping of the electronic structure of Mo species as drawn by DFT and XAS spectra simulation, a model that details the structure of the Mo active sites in the selective oxidation of methanol is proposed.

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Section: ■ Introductionmentioning

confidence: 89%

Investigation of the Reducibility of Supported Oxomolybdate Species for Mapping of Active Centers of Partial Oxidation Reaction: In Situ Mo K-Edge XAS and DFT Study

Souza

Berrier

et al. 2019

J. Phys. Chem. C

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“…In catalysis DRIFTS is appliedt o investigate the adsorptiono fr eactantso no rt he poisoning of the actives ites at the catalyst surface [29c, 43] and the restructuring of catalyst materials. [72] Demoulin et al [8g, 67] used in situ/operando DRIFTS to investigate chemical adsorbates, intermediates and products during the catalytic combustion of CH 4 with Pd/Al 2 O 3 catalysts. They proposed at wo-step reactionS cheme with aPd x 0 -CO species as important surface intermediate.…”

Section: Characterization and Operando Methodology In Gas Sensing Andmentioning

confidence: 99%

Exploiting Synergies in Catalysis and Gas Sensing using Noble Metal‐Loaded Oxide Composites

et al. 2018

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Noble metal/metal oxide nanocomposites are very important in various fields of catalysis and play an evenly important role in gas sensing. Although there are many similarities regarding the choice of materials, the synthesis and the fundamental mechanisms, both research fields have been mostly treated independently up to now. In both fields, open questions regarding the elementary steps in the interaction of the gases with the active species and the role of the noble metal, the semiconducting metal oxide support and the interface remain. In this concept article, we first outline the importance of such composites in catalysis and gas sensing focussing on Pt/Pd, as well as CeO2 and SnO2 as transition metal oxides. Next, the state of art of both fundamental and relevant surface reactions and electronic mechanisms are described. Finally, we highlight the synergy of jointly exploring catalysis and gas sensing of noble metal/metal oxide nanocomposite materials and the benefit for both research fields if they are dealt with simultaneously using advanced characterization and operando methods, sophisticated preparation techniques, testing of the performance, and predictive theoretical modelling.

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“…2,3,5,6,8,15,17,22−30 On this basis, there is strong evidence that under dehydrated conditions, the isolated surface Mo(VI) sites predominantly exist as four-coordinate dioxo Mo(VI) species, although minor five-coordinate monooxo Mo(VI) species can be also present (Figure 1). 3,5,6,14,[22][23][24][25]28 Besides the monomers, dimeric/oligomeric Mo(VI) oxide species or clusters at relatively low Mo loadings were sometimes suggested. 15,26,27 Crystalline MoO 3 is additionally observed for high Mo content.…”

Section: ■ Introductionmentioning

confidence: 99%

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

2020

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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.

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Monitoring Silica Supported Molybdenum Oxide Catalysts at Work: A Raman Spectroscopic Study

Cited by 22 publications

References 46 publications

Investigation of the Reducibility of Supported Oxomolybdate Species for Mapping of Active Centers of Partial Oxidation Reaction: In Situ Mo K-Edge XAS and DFT Study

Investigation of the Reducibility of Supported Oxomolybdate Species for Mapping of Active Centers of Partial Oxidation Reaction: In Situ Mo K-Edge XAS and DFT Study

Exploiting Synergies in Catalysis and Gas Sensing using Noble Metal‐Loaded Oxide Composites

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

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