An attempt to use carbon dioxide as a diluent and oxidant in the dehydrogenation of ethlybenzene to styrene was carried out over an activated carbon-supported iron catalyst (Fe 17 wt.-%) at 773-973 K, CO2/ethylbenzene = 50-70 mol/mol and W/F = 30-120 g h/mol. An addition of 20-30 mol-% lithium nitrate to iron resulted in a significant increase in the catalytic activity. The highest yield of styrene (40-45%) with more than 90% selectivity was obtained at a ratio of lithium to iron of 0.1-0.2 (mol/mol). In addition to styrene, carbon monoxide and water were formed as products. This indicated that the reaction proceeds via an oxidative dehydrogenation mechanism. Added lithium nitrate was converted into lithium ferrite during the treatment of an iron-lithium co-loaded activated carbon catalyst under carbon dioxide at 973 K. Lithium ferrite thus formed would be an active center of the reaction.