Catalytic Upgrading of Biomass Pyrolysis Vapors and Model Compounds Using Niobia Supported Pd Catalyst

This work addresses the effect of the support on the performance of Pd-based catalysts for hydrodeoxygenation of different model molecules (phenol, m-cresol, anisole, guaiacol) in the vapor phase at 573 K. The activity and the selectivity to deoxygenated products strongly depended on the support, regardless the model molecule. For HDO of phenol and m-cresol, benzene and toluene were the dominant products on niobia supported catalysts, whereas cyclohexanone and methylcyclohexanone were the main compounds formed on Pd/SiO₂. For HDO of anisole, demethoxylation reaction producing benzene is favored over Pd/Nb₂O₅ catalyst, while demethylation is the preferred route over Pd/SiO₂. Phenol and methanol were the main products observed for HDO of guaiacol over all catalysts but significant formation of benzene was detected over Pd/Nb₂O₅. The improved deoxygenation performance over the niobia supported catalysts is explained in terms of the oxophilic sites represented by Nb⁴⁺/Nb⁵⁺ cations. These catalysts were also tested for HDO of pine pyrolysis vapors. All three catalysts were effective for reducing the total yield of oxygenated products. The extent of deoxygenation was highest over the Pd/Nb₂O₅ and Pd/NbOPO₄ catalysts. The effectiveness of Pd/Nb₂O₅ and Pd/NbOPO₄ for deoxygenation of real feeds is in good agreement with the model compound results and suggests that these catalysts are promising materials for the upgrading of pyrolysis vapors to produce hydrocarbon fuels.