The mechanism of deactivation of palladium-containing hydrogenation catalysts in the presence of sulfur compounds is discussed on the basis of quantum-chemical calculation of chemisorbates, an analysis of published physicochemical data, and results from our studies and far-IR spectroscopic measurements. The dominant role of the palladium-atom electronic state determined by the character of electron transfer in the support-palladium ion-organosulfur substrate system was shown. It was concluded that catalyst deactivation is due to excess electron density on the catalysts, as well as to additional phenomena of surface blocking by molecular sulfur and by sorption of hydrogen sulfide in support pores and capillaries. The favorable effect of orthoboric acid added to the Pd/Al2O3 catalyst was shown, which is due to both its involvement in electron transfer processes and impediment of access for organic sulfur compounds. The data obtained were correlated with the topochemical and physicochemical properties of catalysts.