Ethylbenzene dehydrogenation over FeO sub(x/(Mg,Zn)(Al)O catalysts derived from hydrotalcites: Role of MgO as basic sites)

A series of Mg sub(3-xZn) sub(x)Fe sub(0.5Al) sub(0).5 mixed oxide catalysts derived from hydrotalcites were tested in the ethylbenzene dehydrogenation to styrene in He atmosphere at 550 [deg]C. The catalysts were prepared by coprecipitation from the nitrates of metal components followed by calcination to mixed oxides at 550 [deg]C. A part of Mg[super]2+ in Mg sub(3Fe) sub(0).5Al sub(0.5 mixed oxide was replaced with Zn[super]2+ to test the effect of MgO as the support. The mixed oxides were composed of periclase and spinel-type compounds with a high surface area of [inline image]. Moessbauer and XPS measurements indicated the presence of Fe[super]3+ on the catalysts and H) sub(2)-TPR measurement suggested that the dehydrogenation reaction is catalyzed by the reduction-oxidation between Fe[super]3+/Fe[super]2+. The activity of Mg sub(3-xZn) sub(x)Fe sub(0.5Al) sub(0).5 mixed oxide decreased with increasing x, indicating an important role of MgO on the activity. Both CO sub(2-TPD measurements as well as IR measurements of adsorbed CO) sub(2) clearly indicated the presence of basic sites of Mg[super]2+O[super]2- on the catalysts. It seems that the combination of Mg[super]2+O[super]2- and Fe[super]3+ was essential for the catalytic activity. It is concluded that the surface base sites generated on O[super]2- bound Mg[super]2+ near Fe[super]3+ sites are responsible for H[super]+-abstraction; the dehydrogenation of ethylbenzene was initiated by the H[super]+ abstraction on Mg[super]2+O[super]2- basic sites, and accelerated by the reduction-oxidation of Fe[super]3+/Fe[super]2+ active species.