Hydrotalcite-derived mixed oxides as catalysts for different C–C bond formation reactions from bioorganic materials

The performance of a hydrotalcite-derived mixed oxide (Mg3AlOx) for the three different aldolization reactions, concerned with the valorisation of biomass derivatives, has been studied in this work. The studied reactions were acetone self-condensation, ethanol condensation for the synthesis of C4 chemicals, and the aldolization of aqueous mixtures of acetone and furfural. The gas phase condensation of acetone generates mesityl oxide (C6) and isophorones (C9) as main products, with high selectivities for mesityl oxide (up to 80%). Reaction of ethanol leads to butanol and 1,3-butadiene, although important amounts of undesired ethylene were found at the highest temperatures. Concerning to the liquid-phase condensation of furfural with acetone, C8 and C13 species were found as reaction products. The performance of the catalysts can be explained in terms of the distribution of acid and basic sites determined by NH3- and CO2-TPD, being needed medium strength basic sites (Mn+–O2− pairs) for the condensation reactions, whereas the presence of acid–base pairs are needed for alcohols dehydrogenation (previous step for the condensation when ethanol is used as reactant). The presence of acid sites also leads to lateral reactions, such as the dehydration of ethanol or the rearrangement of lineal phorones into cyclic compounds (isophorones) in the reaction of acetone.