Carbon-supported bimetallic Pd-Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol

Carbon-supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C, and Ru/C) were characterized and evaluated for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA), aiming at the identification/elucidation of active catalysts for high-yield production of completely hydrodeoxygenated products (e.g., benzene). Phenol was found to be the major intermediate on all catalysts. Saturation of the aromatic ring is the major pathway over the precious metal catalysts, forming cyclohexanone and cyclohexanol, followed by ring opening to form gaseous products. Base metal catalysts exhibit lower activity than the precious metal catalysts, but selectively form benzene along with small amounts of toluene, trimethylbenzene (TMB), and cresol without forming ring-saturated or ring-opening products. Compared with Fe/C and Pd/C, PdFe/C catalysts exhibit a substantially enhanced activity while maintaining the high selectivity to HDO products without ring saturation or ring opening. The enhanced activity of PdFe/C is attributed to the modification of Fe nanoparticles by Pd as evidenced by STEM, EDS, EXAFS, TPR, and theoretical calculations.