An
electric field was introduced into the catalytic oxidation of
lean methane at low temperature over Mn
x
Co
y
catalysts. Mn1Co5 exhibited the best catalytic performance with the light off temperature
(T
50) as low as 271 °C in the electric
field, nearly 60 °C lower than that in a conventional reaction
system. The electric field promoted the formation of octahedrally
coordinated Mn3+ with active oxygen species released from
the reduction of octahedrally coordinated Co3+ in Co3O4 spinel. Also, octahedrally coordinated Mn3+ sites were proven to be the main active sites for methane
catalytic oxidation. With an in situ FTIR technique, it was found
that the oxygen species from the catalyst bulk instead of gaseous
oxygen will adsorb on the octahedrally coordinated Mn3+ sites in the electric field, promoting the activation of CH4 at low temperature. The dehydroxylation process will be accelerated
through the formation of CoO(OH) species that will quickly convert
due to the enhanced reducibility of Co3+ in the electric
field, weakening the inhibition of produced hydroxyl species on active
sites. Based on the experimental results, the mechanism of catalytic
oxidation of CH4 over Mn
x
Co
y
catalysts in an electric field was proposed.
The application of electric field promotes benzene oxidation significantly over Pd/CoxCey catalysts. For 1% Pd loading catalysts, the complete oxidation of benzene can be realized at 175 °C with an electric field under an input current of 3 mA, 79 °C lower than the temperature demanded for complete benzene conversion without electric field. The introduction of electric field can save Pd loading in the catalysts while maintaining high benzene conversion. The characterization experiments showed that CeO2 reduction was accelerated with electric field and created more active oxygen, promoting the formation of active sites on the catalyst surface. The OH removal ability of PdO was enhanced by forming CoO(OH) species, which can easily dehydroxylate since the reduction of Co3+ was promoted by the electric field. The optimized Ce/Co ratio is a balance between oxygen availability and OH removal ability.
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