The mechanism for the dehydrogenation of ethylbenzene over V, Cr, and Fe oxides loaded oil activated carbon, powdered diamond, Al2O3, and MgO was studied in the presence of CO2. Vanadium oxide-loaded catalysts provided higher Styrene yields Wider CO2 than Ar flow. The transient response method was carried out to understand the reaction behaviors of lattice oxygen of various metal oxides on the support. The results showed that lattice oxygen of vanadium oxide (V=O) was consumed in the dehydrogenation reaction and that reduced vanadium oxide was reoxidized with CO2. A similar redox cycle was observed oil iron oxide-loaded activated carbon catalyst. Spectroscopic characterization revealed that vanadium oxide and iron oxide on the Support were reduced to a low valence state during the dehydrogenation reaction, and the CO2 could oxidize the reduced Metal Oxides. In contrast. chromium(III) oxide Was not reduced during dehydrogenation Front these findings, the redox cycle over vanadium oxide- and iron oxide-loaded catalysts was concluded to be all important factor in promoting the catalytic activity with CO2.