LEAN NOX REDUCTION CUZSM5 CATALYSTS - EVALUATION OF PERFORMANCE AT THE SPARK-IGNITION ENGINE EXHAUST

CuZSM5 catalysts, prepared by ion exchange of HZSM5 (Si/Al=80), enable selective lean NOx reduction at the spark ignition engine exhaust. Al l catalysts, even if exchanged to very high copper loading (556% appar ent exchange level) give no evidence for segregated copper oxide phase s. In the presence of water they are easily reduced in vacuum at 550 d egrees C and are stable to redox cycles (O-2, vacuum) treatments. Incr easing Cu content to about 200% apparent exchange level results in inc reasing NOx, CO and HC conversions. From 200 to 550% exchange CuZSM5 c atalysts give similar performances. Preliminary investigation shows th at after catalytic tests there is evidence for CuO formation only in t he copper-richest catalysts.