CoMo catalysts supported on a commercial gamma-Al2O3 modified with B Na or K were prepared in order to analyze the effect of acid-base characteristics on the FCC naphtha hydrotreatment Catalysts were characterized by NH3 TPD IR of pre-adsorbed pyridine and CO2 XPS Raman and XRD In general with either boron or alkaline metal modification the HDS/HYDO selectivity did not significantly improve However it is remarkable that when the alumina was modified to be either more acidic (B) or more basic (K Na) improvements in the ratio between the HDS and the conversion of the internal branched olefin as well as in the ratio double-bond isomerization to HYD of linear olefins were observed For both modifications this fact was related to the promotion of the double-bond isomerization reaction from external to internal positions For alkaline-doped catalysts it was found that the double-bond Isomerization was related to the existence of basic sites For the boron there is a range of bona content (2-3 wt %) where the double-bond isomerization was promoted selectively over the cracking and alkylation reactions because only weak Bronsted acid sites are present Additionally both modifications (Boron or alkaline metals) of alumina led to a decrease in the HDS activity which was found to be related to changes in the distribution of Co and Mo species in the oxide state Alkaline metal introduction led to the formation of alkaline metal molybdates whereas boron introduction increased the proportion of octahedral polymeric Mo species consequently decreasing the dispersion of the Mo phase (C) 2010 Elsevier B V All rights reserved