Carbon dioxide augmented oxidation of aromatic alcohols over mesoporous carbon nitride as a metal free catalyst

Abstract

The catalytic oxidation of primary/secondary alcohols with molecular O₂ to the corresponding carbonyl compounds and acids was studied over mesoporous carbon nitride (MCN) as a metal free catalyst. The aromatic alcohols showed conversions between 34–63% with O₂ whereas in the co-presence of CO₂ augmented conversions (54–91%) with higher selectivities for acids were observed. The quantification of the promotional effect of the synergism in the co-presence of CO₂ was found to be 18–21%. The catalyst and the gaseous mixture were analysed after the reaction with IR spectroscopy, which revealed the formation of surface carbamate and the existence of CO in the gaseous mixture. The kinetic studies revealed that the first order rate constants are higher in the co-presence of CO₂ and that the kinetic ρ, obtained from the Hammett plot, indicated the development of a positive charge on the substrates during the rate determining step.