NOx REDUCTION CATALYST DEVELOPMENT.

The kinetics of ammonia formation was studied to delineate engine conditions for best net NO//x efficiency and to expand the choice of emission control systems. These studies were carried out in the laboratory with exhaust gases generated by a pulse flame generator and rhodium containing catalysts. Catalyst selectivity, NH//3/N//2 was found to vary linearly with the CO/O//2 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 degree F and increases gradually as the NO//x level is decreased from 800 to 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.