Dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of carbon dioxide (CO2) was carried out over silica-supported vanadium catalysts (VOx/SiO2) to investigate the role of CO2 played in this reaction coupling process. A prominent promoting effect of CO2 on EB dehydrogenation is observed; over VOx/SiO2 with a vanadium loading of 0.8 mmol/g-SiO2, ST yield at 550 degrees C in CO2 is 2.05 times higher than that in an inert atmosphere of nitrogen and the catalyst also deactivates much more slowly in CO2. CO2 as a soft oxidant can effectively keep/regain high valence vanadium species that are highly active for EB dehydrogenation, which is then conducive to enhancing EB conversion and suppressing catalyst deactivation. Both carbonaceous deposition and deep reduction of the active vanadium species contribute to the catalyst deactivation; however, CO2 is only effective on alleviating the catalyst deactivation by protecting the high valance vanadium species from deep reduction, but is invalid in suppressing coke formation. (C) 2012 Elsevier Ltd. All rights reserved.