The catalytic performance of Pt dispersed on gamma-Al2O3 is very strongly promoted by sodium in the temperature range 200-500 degrees C under simulated exhaust conditions at the stoichiometric point. Remarkable and unprecedented effects on NO, CO, and C3H6 conversions, as well as enhanced selectivity towards N-2, are found. Addition of Na causes a significant decrease in the temperature of 50% conversion (T-50) for NO, CO, and C3H6 For optimally promoted Pt this temperature is similar to 100 lower than for unpromoted Pt. Similar decreases are observed for the temperatures required for 100% conversion of NO, CO, and C3H6 The selectivity towards N-2 is improved from similar to 75% over unpromoted Pt to similar to 100% over the optimally Na-promoted catalyst. These effects are understandable in terms of the effects of sodium on the relative adsorption strengths of reactant species.