The catalytic reduction of N 2 O by CO on ion clusters of Fe + and benzene was investigated using an ICP/SIFT tandem mass spectrometer. Both Fe + (C 6 H 6 ) and Fe + (C 6 H 6 ) 2 are discovered to be effective in catalyzing the reduction of N 2 O by CO. However, Fe + (C 6 H 6 ) is found to be poisoned by CO in reactions forming Fe + (C 6 H 6 )CO and Fe + (C 6 H 6 )(CO) 2 . On the other hand, Fe + (C 6 H 6 ) 2 does not exhibit any poisoning by CO and so is the better catalyst. FeO + (C 6 H 6 ) 1,2 ions are observed as intermediates in the catalytic cycles. These results also provide the conceptual basis for a synthesis of CO 2 from CO and O atoms catalyzed by Fe + (C 6 H 6 ) and related cluster ions in interstellar environments.