Strong Promotion by Na of Pt/γ-Al2O3 Catalysts Operated under Simulated Exhaust Conditions

The catalytic performance of Pt dispersed on γ-Al2O3 is very strongly promoted by sodium in the temperature range 200–500°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 N2, are found. Addition of Na causes a significant decrease in the temperature of 50% conversion (T50) for NO, CO, and C3H6. For optimally promoted Pt this temperature is ∼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 N2 is improved from ∼75% over unpromoted Pt 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.