Dynamic States of V2O5 Supported on SnO2/SiO2 and CeO2/SiO2 Mixed-Oxide Catalysts during Methanol Oxidation

Jehng, Jih‐Mirn

doi:10.1021/jp980622v

Cited by 42 publications

(18 citation statements)

References 46 publications

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“…36,59,60 Supported vanadium oxide species are stable during methanol oxidation, but some differences are also evident. Upon introduction of a methanol/O 2 /He gas stream both the terminal V O and bridging V-O-V Raman bands decrease in intensity and shift to lower wavenumbers for all the supported vanadia catalysts.…”

Section: Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

Molecular structures of supported metal oxide catalysts under different environments

Bañares

Wachs

2002

J Raman Spectroscopy

365

307

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The use of in situ Raman spectroscopy to study the molecular structures of supported metal oxide catalysts under different environments is reviewed. The molecular structures under ambient (hydrated) and dehydrated conditions are presented. The effect of moisture at elevated temperatures is also presented and discussed with regard to its implications for catalytic phenomena. The molecular structural transformations during C 2 -C 4 lower alkane (LPG) oxidation, methane oxidation, methanol oxidation and selective catalytic reduction of NO with NH 3 reaction conditions are presented. In situ spectroscopy during catalytic reaction with simultaneous activity/selectivity measurement ('operando' spectroscopy) is emphasized owing to its contribution to the fundamental understanding of catalytic performance. The reducibility of the different surface metal oxide species, the relevance of surface coverage (surface monomeric vs polymeric species) and the specific oxide support are discussed when LPG, methane, methanol or hydrogen is the reducing agent. In situ Raman spectroscopy provides molecular-level information about the surface metal oxide species: structures, stability and transformations under different environments. In many cases, the use of complementary spectroscopic techniques results in a more complete understanding of the molecular structure-activity/selectivity relationships for supported metal oxide catalysts.

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Section: Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

Molecular structures of supported metal oxide catalysts under different environments

Bañares

Wachs

2002

J Raman Spectroscopy

365

307

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“…26 It can also stabilize the dispersion of noble metal particles, 27 and CeO 2 -supported vanadia is much more active for methanol synthesis than vanadia dispersed on other supports. 10, 28 Since it is hard to prepare bulk CeO 2 with a high surface area, interest has arisen in dispersing ceria onto high surface area supports. While there have been numerous attempts to disperse ceria on SiO 2 or Al 2 O 3 29-49 or to incorporate cerium atoms into the walls of mesoporous silica, 50-52 these efforts have largely led to the formation of small crystallites of CeO 2 because ceria has a strong tendency to sinter at elevated temperatures.…”

Section: ' Introductionmentioning

confidence: 99%

Synthesis of Different CeO₂ Structures on Mesoporous Silica and Characterization of Their Reduction Properties

2011

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An investigation was performed to establish the effects of precursor composition on the structure of ceria deposited onto mesoporous silicas, MCM-41 and SBA-15. The structure of the deposited ceria was characterized by XRD, TEM, Raman and UV-visible spectroscopy, XANES, and EXAFS. Using Ce(acac) 3 as the precursor resulted in formation of 3 nm diameter ceria particles located predominantly in the mouths of the support pores. Amorphous agglomerates, but with domains of comparable size to those obtained using Ce(acac) 3 , were obtained using Ce(O i Pr) 4 . Much smaller domains and a high degree of dispersion were obtained using Ce(O t Bu) 4 as the precursor. The structure of the deposited ceria affects its reduction-reoxidation properties. Reduction and reoxidation are almost fully reversible for the nanoparticles. Only surface reduction is observed up to 723 K, whereas partial bulk reduction takes place at higher reduction temperatures. In case of the well-dispersed, layerlike Ce species on the silica surface, an extent of reduction similar to that of the nanoparticles is achievable, but upon heating the samples in 10% H 2 /He to 923 K the reduction becomes partially irreversible. The latter effect might be explained by a formation of cerium silicates that prevent the complete reoxidation of the cerium species. ' INTRODUCTIONDispersion of a transition metal oxide on a high surface area support such as Al 2 O 3 or SiO 2 makes it possible to combine the catalytic properties of the transition metal oxide with the high surface area and thermal and mechanical stability of the support. 1 Good illustrations of the manner in which the transition metal oxide is introduced onto the support and the physical properties of the deposited oxide are given for the cases of TiO x , 1-9 VO x , 5,[9][10][11][12][13][14] or MoO x 10,11,15-21 dispersed on high surface area supports. A notable consequence of this approach is the formation of catalytically active sites which are not present on either the support or the bulk transition metal oxide. For example, neither TiO 2 nor SiO 2 is active for the liquid-phase epoxidation of alkenes, but TiO 2 /SiO 2 exhibits high activity and selectivity for this reaction. 6,[22][23][24] The appearance of such novel catalytically active sites has been attributed to the formation of a twodimensional oxide overlayer whose physical properties differ from those of the corresponding bulk oxide. Dispersed transition metal oxides have also been shown to stabilize the dispersion of small metal particles and to enhance the activity of supported metal oxo species. For example, Au particles have been shown to be much more stable on TiO x /SiO 2 than on SiO 2 25 and isolated vanadate species dispersed on TiO x /SiO 2 exhibit turnover frequencies that are up to 60-fold higher than when dispersed on SiO 2 . 7 CeO 2 is a highly reducible oxide exhibiting oxygen storage and release properties that are important for the operation of threeway, automotive exhaust catalysts. 26 It can also stabilize the dispersion of n...

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“…The success of using silica as a support of reducible or acidic oxide species is well described in Refs. [43,44]. Fig.…”

Section: Catalytic Propertiesmentioning

confidence: 98%

Nanocluster iron oxide-silica aerogel catalysts for methanol partial oxidation

Wang

2005

Applied Catalysis A: General

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Dynamic States of V₂O₅ Supported on SnO₂/SiO₂ and CeO₂/SiO₂ Mixed-Oxide Catalysts during Methanol Oxidation

Cited by 42 publications

References 46 publications

Molecular structures of supported metal oxide catalysts under different environments

Molecular structures of supported metal oxide catalysts under different environments

Synthesis of Different CeO₂ Structures on Mesoporous Silica and Characterization of Their Reduction Properties

Nanocluster iron oxide-silica aerogel catalysts for methanol partial oxidation

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Dynamic States of V2O5 Supported on SnO2/SiO2 and CeO2/SiO2 Mixed-Oxide Catalysts during Methanol Oxidation

Cited by 42 publications

References 46 publications

Molecular structures of supported metal oxide catalysts under different environments

Molecular structures of supported metal oxide catalysts under different environments

Synthesis of Different CeO2 Structures on Mesoporous Silica and Characterization of Their Reduction Properties

Nanocluster iron oxide-silica aerogel catalysts for methanol partial oxidation

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Product

Resources

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Dynamic States of V₂O₅ Supported on SnO₂/SiO₂ and CeO₂/SiO₂ Mixed-Oxide Catalysts during Methanol Oxidation

Synthesis of Different CeO₂ Structures on Mesoporous Silica and Characterization of Their Reduction Properties