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

A series of Mg3−xZnxFe0.5Al0.5 mixed oxide catalysts derived from hydrotalcites were tested in the ethylbenzene dehydrogenation to styrene in He atmosphere at 550 °C. The catalysts were prepared by coprecipitation from the nitrates of metal components followed by calcination to mixed oxides at 550 °C. A part of Mg2+ in Mg3Fe0.5Al0.5 mixed oxide was replaced with Zn2+ 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 100–180 m2 gcat−1. Mössbauer and XPS measurements indicated the presence of Fe3+ on the catalysts and H2-TPR measurement suggested that the dehydrogenation reaction is catalyzed by the reduction–oxidation between Fe3+/Fe2+. The activity of Mg3−xZnxFe0.5Al0.5 mixed oxide decreased with increasing x, indicating an important role of MgO on the activity. Both CO2-TPD measurements as well as IR measurements of adsorbed CO2 clearly indicated the presence of basic sites of Mg2+O2− on the catalysts. It seems that the combination of Mg2+O2− and Fe3+ was essential for the catalytic activity. It is concluded that the surface base sites generated on O2− bound Mg2+ near Fe3+ sites are responsible for H+-abstraction; the dehydrogenation of ethylbenzene was initiated by the H+ abstraction on Mg2+O2− basic sites, and accelerated by the reduction–oxidation of Fe3+/Fe2+ active species.

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► Ethylbenzene dehydrogenation.
► Hydrotalcite-derived FeOx/(Mg,Zn)(Al)O catalysts.
► β-H+ abstraction on the Mg2+–O2− basic sites.
► Reduction–oxidation of Fe3+/Fe2+ active sites.