Catalytic Combustion of Lean Methane Assisted by an Electric Field over Mn<i>_x</i>Co<i>_y</i> Catalysts at Low Temperature

Abstract

An electric field was introduced into the catalytic oxidation of lean methane at low temperature over MnxCoy catalysts. Mn1Co5 exhibited the best catalytic performance with the light off temperature (T50) 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 MnxCoy catalysts in an electric field was proposed.