*2.1. Catalyst Preparation*

Hydrotalcite (HT, 2:1 Mg:Al) was prepared by the co-precipitation of Mg and Al nitrates in deionized water. NaOH and Na2CO3 were added dropwise, and the pH was kept constant at 10. The resulting white slurry was left to age overnight under magnetic stirring and without heating: this aging is more advantageous than aging under heating from the point of view of energy consumption; it also produces more amorphous solids that are generally better for catalytic purposes. The slurry was then filtered, and the cake obtained was washed with abundant deionized water. The solid obtained was dried at 100 ◦C for 24 h, ground, and stored in a vial. Calcination at 450 ◦C for 4 h in a muffle furnace (HD—150 muffle furnace, Hobersal, Caldes de Montbui, Spain) transformed HT into the corresponding mixed metal oxide (MMO), which was used for the catalysis as it was, or rehydrated. MMO was rehydrated in the liquid phase by immersing it in deionized water (2 mg MMO/mL), which had previously been bubbled with pure Ar. The mixture was left stirring at 500 rpm for 24 h at room temperature in a sealed vessel, and finally centrifuged, filtered, and dried under vacuum.
