STUDY OF NITRIC-OXIDE REDUCTION OVER SILVER ALUMINA CATALYSTS UNDER LEAN CONDITIONS - EFFECTS OF REACTION CONDITIONS AND SUPPORT/

The reduction of NO over silver/alumina catalysts was studied in a flo w reactor system at W/F (catalyst weight/total flow)=0.024-0.012 g/(ml /s). Silver/alumina was shown to catalyze the reduction of NO by propy lene or propylene/propane mixture in excess oxygen. The catalytic acti vity was attributed to the hydrocarbon-oxidation reactivity of a silve r catalyst. The activity for NO-reduction increased as the oxygen-cont ent in reaction mixture increased from 1.5% to 10%. This effect of oxy gen-content and the temperature range around 500 degrees C for the red uction of NO can be correlated to the activity of hydrocarbon-oxidatio n. The presence of water and sulfur dioxide had adverse effect on the reduction of NO. The adverse effect could be partially compensated by the enhancement of activity using a proper type of alumina. The type o f alumina used had a great effect on the activity of NO-reduction for a silver/alumina catalyst. Preliminary characterization showed that th e average pore size and the pore-size distribution of the alumina coul d be important factors. An active silver/alumina catalyst was prepared with a higher NO-conversion than the best Cu/ZSM5-based catalyst eval uated at Ford under the same reaction conditions in the presence of H2 O and SO2. (C) 1998 Elsevier Science B.V. All rights reserved.