Oxidative dehydrogenation of ethylbenzene to styrene has been studied over Co₃O₄ supported on mesoporous silica (COK-12) with CO₂ as soft oxidant in a fixed bed reactor at atmospheric pressure in the temperature range of 723 to 923K. While COK-12 has been prepared by self-assembly method using long chain ionic surfactant i.e., P123 as template, cobalt oxide supported on COK-12 catalysts with variable Co content have been synthesised by simple wet impregnation technique. All the catalysts were characterized by N₂ adsorption - desorption, XRD, FT-IR, TPR, UV-Vis and XPS techniques. XRD and pore size distribution studies indicate the intactness of mesoporous structure of SiO₂ even after incorporation of Co₃O₄. Presence of Co₃O₄ crystallites were observed beyond 5 wt% Co loading. High ethylbenzene conversion and stable styrene yields have been observed over 3% Co₃O₄/COK-12 catalyst due to the presence of large number of active Co₃O₄ catalytic sites. Enhancement in the activity has been observed with CO₂ as soft oxidant than with N₂ as diluent. This is because of the fact that the liberated H₂ reacts with CO₂ in the form of reverse water gas shift reaction.