Dehydrogenation of Ethylbenzene to Styrene over Magnesium-Doped Hematite Catalysts

Styrene is an important building block of the plastics industry being produced by ethylbenzene dehydrogenation. The commercial catalysts have the disadvantages of deactivation by potassium loss and coke deposition, and chromium toxicity. To overcome these drawbacks, a new catalyst was developed by investigating the effect of magnesium on the catalytic properties of hematite in ethylbenzene dehydrogenation. Hematite was detected for all fresh catalysts and magnetite for the spent ones. Magnesium was found as magnesium ferrite and magnesium oxide, depending on the magnesium amount. Magnesium compounds affect the crystal sizes, the amount of defects and the reducibility of iron oxides, the predominance of each one depending on the composition of the solids. These effects caused important differences in activity, selectivity and stability of the catalysts. The catalyst with Mg/Fe = 0.09, consisting of aggregates of hematite, MgO and magnesium ferrite, showed the highest yield, being the most promising for commercial applications.