Bimetallic effects in the hydrodeoxygenation of meta-cresol on γ-Al2O3 supported Pt-Ni and Pt-Co catalysts

The hydrodeoxygenation (HDO) of meta-cresol, a typical phenolic compound in bio-oils, is investigated in the vapor-phase on gamma-Al2O3-supported Pt catalysts at near atmospheric hydrogen pressure. The HDO reaction yields two major hydrocarbons: toluene and methylcyclohexane. The deoxygenation of meta-cresol proceeds through two consecutive steps: hydrogenation of the aromatic ring on the Pt metal followed by dehydration reactions of the produced alcohol intermediates on the alumina support. Phenolic ring saturation is proposed to be slower than its sequential dehydration steps on Pt/gamma-Al2O3. This is in a good agreement with the higher selectivity of toluene compared to that of the hydrogenated cyclic hydrocarbon, methylcyclohexane, because toluene formation requires fewer ring hydrogenation steps than its counterpart. The additions of Co and Ni into Pt not only improve the overall HDO conversion, but also modify the product distribution. The enhancement in the overall HDO activity is related to the better hydrogenation activity of bimetallic Pt-Co and Pt-Ni catalysts and the generation of additional sites for alcohol dehydration. Consequently, more saturated cyclic hydrocarbon product, methylcyclohexane, is observed on bimetallic catalysts with respect to the monometallic Pt catalyst.