Catalytic hydrodeoxygenation of lignin model compounds over NiMo/Al2O3 and CoMo/Al2O3

Catalytic hydrodeoxygenation of a mixture of lignin model compounds (biphenyl, benzyl phenyl ether and vanillyl alcohol) was performed over NiMo/Al2O3 and CoMo/Al2O3 in a batch reactor. The catalysts were synthesized through wetness impregnation over commercial γ-Alumina. The chosen feedstock was subject to different reaction conditions in terms of temperature, pressure and reaction time and the results were reported. The effect of the catalyst loading was also investigated (20 wt% vs 40 wt%). Under the same operational conditions, conversion, selectivity and yield were calculated and compared among the two catalysts used. Characterization of the catalysts was carried out via X-Ray Diffraction (XRD), N2 desorption and NH3-Temperature Programmed Desorption (NH3-TPD) and the reaction products were analysed via GC-MS. The results showed total conversion (100%) of benzyl phenyl ether and vanillyl alcohol and no conversion of biphenyl for all the experiments after 4 h. The selectivity was significantly higher towards substituted cyclohexanes and more saturated compounds using NiMo/Al2O3 and towards oxygenated aromatics using CoMo/Al2O3, showing different activity of the two catalysts. Furthermore, NiMo/Al2O3 led to a higher amount of condensed compounds compared to CoMo/Al2O3. Reaction mechanisms operated by the two catalysts were hypothesized in order to understand the behaviour of the model compounds during reaction progress.