Hydrodeoxygenation of Phenol as a Model Compound for Bio-oil on Non-noble Bimetallic Nickel-based Catalysts

Ni/HZSM-5 catalysts for the hydrodeoxygenation of bio-oil were modified with Cu and Co. A first test series with phenol as a model revealed that the presence of Ni is essential for high activity. However, modification with Cu deteriorated the catalytic performance significantly whereas an admixture of Co increased the activity and selectivity toward the target hydrocarbons benzene and cyclohexane. Characterization studies performed by using TEM, X-ray photoelectron spectroscopy, and XRD techniques elucidated detrimental effects of the second metals: both Cu and Co form alloys with Ni; however, Cu caused a loss of active sites as well as tended to segregate at the surface whereas Co made the particles smaller and strongly stabilized the active Ni sites, that is, Ni dispersion increased. A Ni-Co/HZSM-5 catalyst (10 wt% of each metal content) showed 99% hydrocarbon selectivity at complete phenol conversion. Additional studies using intermediate products such as benzene, cyclohexene, and C-6 oxygenates as feeds highlight the effect of the catalyst composition on key reaction steps.