Synthesis, Characterization, and Catalytic Behavior of Mg-Al-Zn-Fe Mixed Oxides from Precursors Layered Double Hydroxide

In the present work, Mg-Al-Zn-Fe layered double hydroxides (LDH) were prepared by coprecipitation reaction with hydrothermal treatment. Their corresponding calcinated products (mixed oxides) were used as catalyst for ethylbenzene dehydrogenation to styrene. The characterization of precursors and the mixed oxides was carried out by X-ray diffraction, XPS, TGA-DSC, UV-vis-DRS, specific surface area, and magnetic properties. The Fe3+ species were detected by XPS; they exist in two chemical states related to oxides and spinel environment. Zn is found in two possible contributions, such as ZnO or spinel. XRD data indicate that the hydrotalcite phase exists in all precursor samples, except for the sample without magnesium (HT100). In the mixed oxides the ZnO phase increases with the rise of the Zn content. Oxides show a decrease of surface areas with the increase of the Zn content. Ethylbenzene dehydrogenation was carried out with the mixed oxides synthesized. The HT25 sample with Zn/(Zn + Fe) = 0.25 molar ratio shows a 31.5% conversion and selectivity to styrene superior to 87%, which is directly related to the quantity of oxide, spinel phase and magnesium, as well as the high surface area and the magnetic response obtained.