Hydrodeoxygenation of Phenolic Compounds by Sulfided (Co)Mo/Al2O3Catalysts, a Combined Experimental and Theoretical Study

The hydrodeoxygenation of model phenol compounds (phenol and 2-ethylphenol) was carried over unpromoted Mo/Al2O3 and promoted CoMo/Al2O3 catalysts. Hydrodeoxygenation proceeds by two pathways:– hydrogenation of the aromatic ring followed by Csp3-O bond cleavage (HYD pathway, (hydrogenation of the aromatic ring followed by Csp3-O bond cleavage));– direct cleavage of the Csp2-O bond (DDO pathway).Both routes were favored by the presence of Co on the catalyst, while the presence of the alkyl substituent on the phenolic ring favors the DDO route but inhibits the HYD pathway. IR (InfraRed) spectroscopy shows that while phenol mostly dissociates on these catalysts, a significant fraction of 2-ethylphenol remains non dissociated. The adsorption energies of both reactants and possible reaction intermediates on promoted and non-promoted sulfide phases as computed by DFT (Density-Functional Theory) confirm these findings and allow rationalizing the catalytic activity trends observed experimentally.