||In this work, the n-heptane transformation was carried out in absence and presence of 1.2 wt\% of guaiacol over Ni- and V-impregnated zeolites at 450 degrees C, to evaluate the influence of these metals on the poisoning effect of phenolic molecules during bio-oils and traditional Fluid Catalytic Cracking (FCC) feedstocks co-processing. Impregnation of the metals slightly decreased the Bronsted acid sites, but importantly increased the Lewis acidity. Notably, guaiacol was found to be less poisonous at shorter time-on-streams when Ni or V were present on the zeolite, as the metal-induced Lewis acidity seems to promote guaiacol transformation, which slows down coke formation from n-heptane. Simultaneously, unconverted guaiacol molecules adsorb mainly on the Lewis acid sites, resulting in a higher number of Bronsted acid sites available for the cracking reactions. Influence of Ni on the attenuation of the guaiacol deactivating effect was more important owing to the generation of a higher amount of metal-induced Lewis acid sites. Hence, taking into account the short contact times in the FCC riser, the presence of metal contaminants, such as Ni and V, on the FCC catalysts appears to be beneficial for the co-processing, being possibly one of the explanations for the lower impact of the phenolic compounds on the FCC equilibrium catalyst when compared to pure ultra-stable Y zeolites.