Molybdena on Silica Catalysts: Role of Preparation Methods on the Structure-Selectivity Properties for the Oxidation of Methanol

Bañares, Miguel Á.; Hu, Hangchun; Wachs, Israel E.

doi:10.1006/jcat.1994.1359

Cited by 119 publications

(101 citation statements)

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“…Increasing the surface molybdenum oxide coverage decreases the Raman intensities of these bands owing to titration of the Si-OH sites by the deposited Mo oxide, which demonstrates that the molybdenum oxide is well dispersed on the silica support. The dispersed and isolated surface molybdenum oxide species (¾980 cm 1 transforms into microcrystallineˇ-MoO 3 (Raman bands at 842 and 768 cm 1 during methanol oxidation at 503 K. 59,62 At very low surface molybdenum oxide coverage, this aggregation is hardly appreciable, probably owing to the low probability of interaction among the surface molybdenum oxide species. However, the formation of the microcrystallině -MoO 3 phase becomes more intense with increasing surface molybdenum oxide loading, at ¾5% MoO 3 /SiO 2 [ Fig.…”

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

“…This is the reason for the progressive decrease in the apparent TOF values for methanol oxidation with surface molybdenum oxide coverage on silica. 62 The decrease in methanol conversion with surface molybdenum oxide coverage is mainly due to this sintering phenomenon and results in a significant decrease in the methyl formate formation while HCHO production shows a smoother decrease with surface molybdenum oxide loading. These trends depend only on the surface molybdenum oxide coverage and are essentially independent of preparation method and the specific silica support.…”

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

“…These structural effects account for the significant decrease in methanol conversion to methyl formate that requires both adjacent surface molybdenum oxide species and exposed surface silanol sites. 62 The in situ Raman spectra of 5% Re 2 O 7 /SiO 2 under methanol oxidation reactions conditions exhibit the vibrations of surface Si-OCH 3 (Raman bands at 2956 and 2856 cm 1 ). 59 The catalyst also exhibits Raman bands at 1010, 973 and 340 cm 1 [ Fig.…”

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

“…The Mo-OCH 3 species were also somewhat volatile because Mo deposits were detected on the glass portion of the reactor exit. 62 The strong interaction of surface molybdenum oxide species with methanol that leads to its structural rearrangement into microcrystallineˇ-MoO 3 also affects the stability of silica-supported silicomolybdic acid, which at 573 K under methanol oxidation reaction conditions formš -MoO 3 . 61…”

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

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Molecular structures of supported metal oxide catalysts under different environments

Bañares

Wachs

2002

J Raman Spectroscopy

361

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: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

Section: Under Methanol Oxidation Reaction Conditionsmentioning

confidence: 99%

See 2 more Smart Citations

Molecular structures of supported metal oxide catalysts under different environments

Bañares

Wachs

2002

J Raman Spectroscopy

361

307

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“…indicates the absence of bands related to either tetrahedral coordinated Mo ions (230 nm) (35,36) or bulk MoO 3 , which used to appear as a broadband near 330 nm (38).…”

Section: Ir Study Of Mo-encapsulated Dealuminated Mordenitementioning

confidence: 99%

Effect of Mordenite Dealumination on the Structure of Encapsulated Molybdenum Catalysts

Mohamed

Salama

2002

Journal of Colloid and Interface Science

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Raman Spectroscopy of Catalysts

Bañares

Wachs

2010

Encyclopedia of Analytical Chemistry

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This chapter focuses on the application of Raman spectroscopy for characterizing catalytic materials and for the investigation of the bulk and surface chemistry occurring during catalyst preparation and operation; a general theoretical background and description of equipment for Raman experimentation is also presented. Over the past decades, Raman spectroscopy has increasingly been applied for characterization of all types of catalytic materials: bulk and supported metals, bulk mixed metal oxides, supported metal oxides, bulk and supported metal sulfides, zeolites and molecular sieves, heteropolyoxo anions, and clays. Raman is also used to study chemisorption and, in recent years, Raman has been increasingly applied under in situ conditions. There is an increasingly important strong driving force leading research toward the study of catalysts under reaction conditions. The last few years exhibit an increasing number of Raman studies during relevant reaction conditions (operando methodology). This momentum in reaction and operando Raman spectroscopy advances a new revolution in catalysis science that is poised to afford accurate molecular understanding of catalytic structure–activity/selectivity relationships.

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Molybdena on Silica Catalysts: Role of Preparation Methods on the Structure-Selectivity Properties for the Oxidation of Methanol

Cited by 119 publications

References 0 publications

Molecular structures of supported metal oxide catalysts under different environments

Molecular structures of supported metal oxide catalysts under different environments

Effect of Mordenite Dealumination on the Structure of Encapsulated Molybdenum Catalysts

Raman Spectroscopy of Catalysts

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