The effect of Cu content on the hydrodeoxygenation performance of Cu(x)MgFeO ex-LDH mixed oxide catalysts

Cu(x)MgFeO mixed oxides(with Mg/Fe = 3 and 2.5 ≤ x ≤ 20 at. %) were obtained from layered double hydroxides (LDH) precursors, characterized and tested in the hydrodeoxygenation reaction of benzyl alcohol. The LDH precursors were prepared through coprecipitation, then dried and calcined at 500 ⁰C. The solids were characterized by XRD, N₂ adsorption-desorption, H₂-TPR, CO₂-TPD and SEM-EDX techniques. Catalytic tests were performed in an autoclave reactor under 5 atm of H₂. The influence of Cu loading (2.5 – 20 at. % with respect to cations), reaction temperature (150 – 230 °C), and reaction time (15 min – 5 h) were investigated.

XRD patterns of the precursors showed typical reflections for the LDH structure, with no segregated phases, except for the sample with 20 % Cu. The mixed oxides showed, besides the periclase phase, the presence of MgFe₂O₄. The sample with 20 % Cu also showed diffraction lines for CuO. All mixed oxides presented high specific surface areas and mesoporous structures. High hydrogen consumptions, corresponding to the reduction of both Fe and Cu species, were observed in H₂-TPR measurements, while CO₂-TPD confirmed the presence of low and medium-strength basic sites.

With 94 % alcohol conversion and 94 % selectivity for toluene, Cu(10)MgFeO was the best catalyst in this series. The influence of reaction temperature and reaction time were also studied. Catalytic tests using benzaldehyde and benzyl benzoate as reactants confirmed them as reaction intermediates. The catalytic performances of the Cu(x)MgFeO catalysts were correlated with the basicity and reducibility results.