Activity and N2 Selectivity of Sol–Gel Prepared Pt/Alumina Catalysts for Selective NOx Reduction

We prepared 1 and 2 wt% Pt/Al2O3 catalysts by a single-step sol–gel process and tested their activity and N2 selectivity for NOx reduction with propene. Our results show that when compared to the impregnation catalysts, the single-step sol–gel catalysts have superior N2 selectivity both in terms of percentage of NO converted to N2 (∼70% or greater) and comparable activity. All of the catalysts tested show a minimum in N2 selectivity at the point of maximum NOx conversion. Both the value of the minimum selectivity and the NOx conversion are functions of oxygen concentration in the feed. The N2 selectivity at peak conversion exhibits a minimum at ∼6.8% O2. Increasing the feed oxygen concentration beyond 6.8% has many beneficial effects including broadening of the temperature window, suppression of NO2 formation and increasing the N2 selectivity without significantly changing the maximum NOx conversion. The sol–gel catalysts show remarkable robustness after exposure to high temperatures, SO2, and long time exposure to reactants.