Abstract
The catalytic properties of nanostructured MAl 2O 4 (M = Cu, Ni, Fe or Mg) were investigated in the dehydrogenation of ethylbenzene with CO 2. The catalysts were characterised by XRD, Raman spectroscopy, textural properties, acidity (TPD-NH 3) and basicity (CO 2-TPD) measurements, SEM and TEM analyses and TPR techniques. XRD revealed the spinel structure of MAl 2O 4, except for the NiO, CuO, Fe 2O 3 and MgO phases. All solids exhibited the nanostructured features of the SBA-15 template, including high values of textural properties and morphologies characteristic of the mesoporous silica. The acidic strength follows the electronegativity trends of the cations present on the spinel aluminates: CuAl > NiAl > FeAl and MgAl, which is the inverse order of the basicities. The selectivities in the dehydrogenation of ethylbenzene with CO 2 showed that styrene was the predominant product for all catalysts except for those based on Ni, which was highly selective for the production of toluene. The FeAl 2O 4 catalyst provided the best catalytic performance among the solids studied due to the continuous oxidation of Fe 3+ sites by the CO 2 from the reaction. This solid has the additional advantage of being stable over the timescale of the reaction, as compared to the traditional Fe-based catalysts, due to its nanostructured features.
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