Selective Vanillin Hydrodeoxygenation on Synthetic Takovite Derived NiAlO_x Mixed Oxide

A mixed metal-oxide (NiAlO_x) obtained from the annealing of a synthetic takovite clay, [(Ni₆Al₂(OH)₁₆]CO₃·4H₂O, was used as a catalyst in the hydrodeoxygenation reaction of vanillin, as a model molecule, to simulate deoxygenation of lignin's moieties. The catalysts were characterized by XRD, TPR, XPS and textural analyses and were tested at between 413 and 573 K and 1.2 MPa H₂, using a 300 ml batch reactor. The reaction products were analyzed using a gas-chromatograph coupled to a mass detector (GC–MS). The active site is visualized as a Ni^δ+–O–Al³⁺ moieties able to dissociate molecular H₂ into highly reactive species (H⁻ and H⁺) for hydrogenation reactions. Depending on the reaction temperature, decarbonylation, hydrogenation, demethoxylation and dehydroxylation reactions occurred in three stages as clearly indicated by Van-Krevelen O/C* vs. H/C* plots. Our study points out that total deoxygenation can be attained at 553 K with a 100% selectivity to products like methyl-cyclohexane and cyclohexane.