This paper reports the interaction of aromatic compounds (as phenol, ethylphenols, and guaiacol) representative of oxygenated functions of pyrolysis bio-oils, with sulfided (Co)Mo/Al2O3 catalyst in order to determine the origin of catalyst deactivation in hydrodeoxygenation (HDO) reaction. Infrared spectroscopy shows that all the studied phenolic compounds anchor on the alumina support as phenate-type species, whereas only the most basic ones (2(4)-ethylphenol and guaiacol) interact also with the sulfide phase. At 623 K (typical temperature of the HDO reactions), only phenate species on the support are formed that is confirmed by study of the catalyst tested in HDO reaction. Phenate-type species anchored on alumina hinder the accessibility of the sulfide edge sites. This shows that the nature of the oxygenated compound (basicity and nature of the substituent) as well as the surface properties of the catalyst support are crucial in the mode and extent of HDO active sites poisoning. (c) 2012 Elsevier Inc. All rights reserved.