The reduction of NO by CO over Rb-promoted Pt/γ-Al 2 O 3 catalysts has been investigated over a wide range of temperature (ca. 200-500 o C), partial pressures of reactants and promoter loadings. For purposes of comparison, K- and Cs-promoted Pt/γ-Al 2 O 3 catalysts were tested under the same conditions. Rubidium strongly enhanced both catalytic activity and N 2 -selectivity. Rate increases by factors as high as 110 and 45 for the production of N 2 and CO 2 , respectively, relative to unpromoted Pt were obtained, accompanied by substantial increase in N 2 -selectivity (e.g. from 24 to 82% at 350 o C and [CO]=0.5%, [NO]=1%). Under stoichiometric conditions, Rb-promoted catalysts gave 100% conversion of both reactants with 100% selectivity towards N 2 at T~350 o C and at an effective reactant contact time of only ~0.5s. In contrast, under the same conditions unpromoted Pt delivered <30% conversion and poor N 2 -selectivity (approximately <40%); even at 480 o C the conversion was only ~60%. The observed promotional effects are ascribed to alkali-induced changes in the chemisorption bond strengths of CO, NO and NO dissociation products which lead to the observed activity enhancement and dependence of N 2 -selectivity on promoter loading. The effects of K-promotion mirror those of Rb-promotion, but are significantly less pronounced. Rb is the best alkali promoter.