Vanadium species in new catalysts for the selective oxidation of methane to formaldehyde: Activation of the catalytic sites
Résumé
New vanadium oxide supported on mesoporous silica catalysts for the oxidation of methane to formaldehyde were investigated by infrared and Raman spectroscopies to identify and characterize the molecular structure of the most active and selective catalytic sites. In situ and operando experiments have been conducted in order to understand the redox and hydroxylation/dehydroxylation processes of the vanadium species. (SiO)2VO(OH) species were identified in these catalysts in reaction conditions and shown to undergo a deprotonation at 580 8C under vacuum, leading to a site giving a photoluminescence band at 550 nm attributed to reverse radiative decay from the excited triplet state: (V4+–O-)* ?(V5+ O2-). An activation mechanism of vanadium monomeric species with electrophilic oxygen species is proposed.
Mots clés
Supported vanadium oxide
Mesoporous silica
Heterogeneous catalysis
Methane oxidation
Formaldehyde
Operando Raman spectroscopy
In situ IR spectroscopy
Hydroxylated monomeric vanadium species
Electrophilic oxygen species
"Supported vanadium oxide"
"Mesoporous silica"
"Heterogeneous catalysis"
"Methane oxidation"
"Formaldehyde"
"Operando Raman spectroscopy"
"In situ IR spectroscopy"
"Hydroxylated monomeric vanadium species"
"Electrophilic oxygen species"