The adsorption of phenol on supported sulfide CoMo catalysts and on oxides is investigated using IR spectroscopy. On silica, phenol mainly interacts via hydrogen-bonding, whereas on alumina it dissociates on the acid-base pairs of this oxide leading to the formation of strongly adsorbed phenolates species. On a sulfided CoMo catalyst supported on alumina, phenol dissociates on the support but does not interact strongly with the sulfide phase. The accessibility of the various sites of the catalyst after phenol contact is investigated by CO adsorption monitored by IR spectroscopy. As expected, phenolate formation decreases the accessibility of support sites. In addition, a decrease of the sulfide site accessibility is also observed. This is indicative of an indirect poisoning of the sulfide edge sites by phenolate species anchored on the support and in the vicinity of sulfide slabs. Consequently, decreasing the amount or strength of the acid-base paired sites of the support should be a way to limit deactivation. (C) 2011 Elsevier B.V. All rights reserved.