Evaluates the use of selective catalytic NOx reduction (5CR) in the early spring of 1980 using ammonia (NH3) and a surface active catalyst to reduce NO compounds to nitrogen and water. The ammonia selectively”eacts with oxygen associated with the N0 rather than the free oxygen in the exhaust gas. This feature makes the method especially attractive for those IC engines that are designed to run fuel—lean (lean—burn). This includes all two—cycle and most turbocharged four—cycle engines.