(167e) Furfural Deoxygenation Over Carbon-Supported Noble Metal Catalysts

Catalytic upgrading of fast-pyrolysis oils via hydrodeoxygenation (HDO) provides a viable approach for producing liquid transportation fuels from lignocellulosic biomass.  Recent bio-oil upgrading research has demonstrated that carbon-supported noble metal catalysts, in particular Pd/C and Ru/C, provide higher yields of liquid products with lower oxygen contents than conventional hydrotreating catalysts, NiMoS/Al₂O₃ and CoMoS/Al₂O₃.¹  In this work, HDO of furfural, a hemicellulose pyrolysis model compound, was performed in a fixed-bed flow micro-reactor over Pd/C, Ru/C and PdRe/C catalysts at 200°C and 1 atm H₂.  Two on-line gas chromatographs were employed for product analysis. Three main reaction pathways were observed: decarbonylation to furan, hydrogenation to furfuryl alcohol, and HDO to 2-methyl furan.  Furan ring-opening products were not observed over any of the catalysts under these reaction conditions. Saturation of the furan ring was observed resulting in additional products: tetrahydrofuran (THF), tetrahydrofurfuryl alcohol, and 2-methyl THF.  C₁ products included carbon monoxide, carbon dioxide, formaldehyde, methanol and methane.  Pd/C was selective for furfural decarbonylation, yielding furan/THF and a stoichiometric quantity of CO.  Furfural hydrogenation was also observed over Pd/C; furfural HDO was insignificant under these conditions.  The observed catalytic performance of Pd/C is consistent with previous data for furfural HDO over Pd/SiO₂.²  In contrast, PdRe/C produced nearly equal selectivity to decarbonylation and HDO.  With regard to C₁ product selectivity, PdRe/C generated a small stoichiometric quantity of CO₂, indicative of water-gas shift activity.  In comparison, Ru/C was selective to decarbonylation with markedly less ring saturation than either Pd/C or PdRe/C.  The catalysts were characterized by CO chemisorption, temperature-programmed reduction, temperature-programmed hydride decomposition (TPHD), and extended x-ray absorption fine structure (EXAFS) spectroscopy.  The bimetallic catalyst consisted of segregated Pd and Re nanoparticles as evidenced by EXAFS spectra at the Pd K- and Re L_III-edges and by TPHD, which indicated that a β-Pd hydride phase decomposes under 5% H₂at 55ºC.

References:

1.         Wildschut, J.; Mahfud, F. H.; Venderbosch, R. H.; Heeres, H. J. Ind. Eng. Chem. Res. 2009, 48, (23), 10324-10334.

2.         Sitthisa, S.; Resasco, D. E. Catal. Lett. 2011, 141, (6), 784-791.