The selective non-catalytic reduction of nitric oxide using ammonia at up to 15% oxygen

Selective non-catalytic reduction of nitric oxide (NO) using ammonia was studied with up to 15% (by volume) oxygen at 102 kPa. The experiments were conducted in an electrically heated laminar-flow, quartz reactor using mixtures of N₂, O₂, NO, and CO to simulate exhaust gas. The base case condition included 330 ppmv of NO, 495 ppmv of NH₃, and 15% O₂. At a reactor temperature of 1050 K, 77% of the NO was removed. For a lower oxygen concentration of 1%, the NO removal was as high as 98% at 1100 K. The degraded performance at high oxygen concentrations is attributed to increases in the oxidation reactions. A major result of this work was the quantification of the amount of N₂O in the treated gases. For the base case conditions, 21 ppmv of N₂O was measured for a reactor temperature of 1075 K. Increasing the ratio of NH₃ to NO (by increasing the NH₃ concentration) increased the maximum NO removal and decreased the temperature at which this level of NO removal was achieved. For the higher NH₃ concentrations, however, the N₂O concentration increased to as high as 54 ppmv. The oxidation products of ammonia (in the absence of NO) for these conditions were found to include first N₂O beginning at 900 K and then NO beginning at 1050 K. Comparisons between these experimental results and predictions from the Miller and Bowman (1989) model indicate that further enhancements of the model may be necessary to incorporate the features of high oxygen conditions.