Tuning the selectivities of Mg-Al mixed oxides for ethanol upgrading reactions through the presence of transition metals

The effect of the presence of reduced Co and Ni (chosen as representative metals because of their good activity for dehydrogenation reactions) on the catalytic performance of basic mixed oxide (Mg-Al) for ethanol condensation is studied in this work. This effect has been studied both in absence and in presence of hydrogen, and considering the different steps of this complex reaction. Globally, best results were obtained with Co/MgAl, under reducing atmosphere, at mild temperature (below 600 K). At these conditons, 1-butanol production rates are up to eight times higher than the obtained with Mg-Al under inert atmosphere. Co has a marked activity in the dehydrogenation step, that prevails over its less relevant activity in aldolization and hydrogenation reactions. This result indicates the relevant role of this first reaction step. DRIFT spectroscopy analyses were carried out to support the experimental results and to identify the role of hydrogen and metals on the oligomerization and permanent adsorption processes, which can produce the deactivation of the catalyst.