A combined operando DRIFT and SSITKA study of the methanation reaction over Ni/alumina catalysts is proposed in the absence and in the presence of various poisons representative of bio-mass gasification into syngas. In a detailed kinetic model derived from the direct inventory of the reacting surface, the rate of hydrogenation is shown to be controlled by the probability for a dihydrogen molecule to collide with an active site constituting two adjacent Ni atoms free from adsorbed CO, and free from adsorbed poisons. From this analysis, N-containing poisons (ammonia, acetonitrile) exhibit a rather mild poisoning effect, while Cl-containing molecules such as trichloroethylene are strongly but reversibly decreasing the methanation activity. No specific effects were observed for tar-like representatives such as toluene or other aromatic molecules.