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The removal of traces of highly unsaturated compounds, such as 1,3-butadiene, from olefin feedstocks via selective hydrogenation is of particular importance because the oligomerization of these impurities produces deactivation and an increased pressure drop across the catalytic beds used in the polymerization processes. The present work focuses on the selective hydrogenation of 1,3-butadiene in the presence of 1-butene using (xCeO2-)Al2O3-supported NiPd catalysts (x = 0, 1, 2, and 3 wt% CeO2) in both liquid and gas conditions. The samples were characterized by XRD, N2 physisorption, Zeta potential, H2-TPR, NH3-TPD, HRTEM and STEM-HAADF. Modifying the catalysts with CeO2 resulted in an increase of 1,3-butadiene conversion, an enhancement of 1-butene selectivity and a decrease of butane production under liquid phase conditions. In contrast, in the gas phase both the Ce-modified and unmodified catalysts behaved similarly: while the fresh catalysts showed similar reactivity to that found in liquid phase conditions, the reacted and thermally pretreated catalysts showed increased reactivity, leading to full hydrogenation up to butane. The improvements observed under liquid phase conditions may be related to modification of the acid strength with increasing CeO2 loading, which would increase the adsorption of 1,3-butadiene and diminish the further hydrogenation of 1-butene. Optimal activity and selectivity were observed for the catalyst with an Ni/Pd atomic ratio of 1, and loadings of 0.5 wt% Pd and 3.0 wt% CeO2.