By means of XPS, ESR, DTA, and pyridine flash desorption techniques; micropulse reactor studies; and quantum-chemical calculations, it was shown that, during the coking of platinum-alumina catalysts in hydrocarbon media, the electron density of the platinum atom increases up to the formation of Pt-0, which is a deactivating factor from the viewpoint of the electronic effects. The stabilization of the activity of platinum-alumina catalysts consists in an increase in the effective positive charge on the platinum atom; this function is fulfilled by modifier elements. It was found that the platinum protection mechanism differs, depending on the nature of the modifying additive: certain elements function via another, additional mechanism of catalyst stabilization, the blocking action. The theoretical conclusions made in this study are corroborated by the results of testing a new, Pt-Sb-Re catalyst supported on Al2O3-Cl with predicted properties.