Mesoporous carbon nitrides (MCN) were prepared by a nano-casting method using mesoporous silica as a template with different carbon and nitrogen sources like melamine only (MS-MCN), urea-formaldehyde (UF-MCN) and melamine-glyoxal (MG-MCN). These mesoporous carbon nitride materials possess nitrogen moieties which behave like a CO₂-philic surface facilitating oxidation of cyclic olefins by molecular oxygen in the co-presence of CO₂ below supercritical conditions. The co-presence of CO₂ augmented the conversions of cyclic olefins at low pressures of CO₂, depicting a promotional effect. Approaches towards quantification of promotional effects and insights into the promotional aspects have been studied.