Dehydrogenation of ethylbenzene with carbon dioxide using activated carbon-supported catalysts

Dehydrogenation of ethylbenzene to styrene under excess carbon dioxide flow was carried out over activated carbon-supported metal oxide catalysts (Cr, Mn, Co, Ni, Mo, Ru, La, and Ce) at 823 K and W/F = 35 g of catalyst.h/mol. The highest yield of styrene (about 40%) with selectivity of above 80% was obtained using activated carbon-support-ed chromium oxide (Cr/AC) and ceri um oxide (Ce/AC) catalysts. The initial activities of the Cr/AC and Ce/AC c atalysts were comparable to that of an iron-loaded activated carbon catalys t reported previously. Only chromium(III) oxide and cerium(IV) oxide were d etected by X-ray diffraction before and after reactions at higher loading l evels, and these species might have been active forms. However, a reduced c hromium oxide species was detected by X-ray photoelectron spectroscopy afte r reaction under argon. In addition to the produced styrene, equivalent amo unts of carbon monoxide and water were formed. These results suggest that t he dehydrogenation of ethylbenzene to styrene proceeds via two reaction pat hs. One is the simple dehydrogenation and an oxidation reaction of hydrogen formed with carbon dioxide. The other is the oxidative dehydrogenation of ethylbenzene through the redox cycle of chromium(III) oxide.