The promotional effects of Sn on Pd/SiO 2 have been investigated by the comparison of Pd/SiO 2 and Pd-Sn/SiO 2 activity in the hydrogenation of maleic anhydride and succinic anhydride to β₯-butyrolactone, and XPS measurement. When reduced at 200 β’ C, both catalysts showed a strong dependence on the reactants, and the addition of tin led to an increase of β₯-butyrolactone yield. When reduction temperature was increased to 350 β’ C, however, the influence of the reactants in the activity disappeared in the case of Pd-Sn/SiO 2 . The disappearance of the feed effect may be suggested to be due to a decrease of the adsorption strength of maleic anhydride on active sites induced the formation of bimetallic Pd-Sn sites. A decrease of the deactivation rate found on Pd-Sn/SiO 2 can also be explained by the decreased rate of polymerization due to the diminution of the adsorption strength of maleic anhydride on Pd-Sn sites. As a result, it is proposed that Pd-Sn/SiO 2 catalyst can be an effective one-step catalyst for hydrogenation of maleic anhydride to β₯-butyrolactone.