NOx Reduction Catalyst Development

As part of recent IIEC-2 activities, we have studied kinetics of ammonia formation to delineate engine conditions for best net NO_x efficiency and to expand the choice of emission control systems. These studies have been carried out in the laboratory with exhaust gases generated by a pulse flame generator and rhodium containing catalysts. Catalyst selectivity, NH₃/N₂ was found to vary linearly with the CO/O₂ ratio in the exhaust gas and with the reciprocal of the space velocity. The effects of temperature and input NO_x levels are more complex: Selectivity shows a maximum in the range of 750-1300°F and increases gradually as the NO_x level is decreased from 800 - 100 ppm. Based on these results a mechanism is proposed for ammonia formation and a triple-catalyst system is suggested for increasing net NO_x efficiency.