The catalytic chemistry of nitric oxide: I. The effect of water on the reduction of nitric oxide over supported chromium and iron oxides

The reduction of NO with CO over alumina supported iron oxide and chromium oxide is a relatively fast process. The reaction is strongly inhibited over both catalysts by small amounts (~0.7 mole %) of water. The reduction of NO by H 2 appears to be significantly slower than by CO, although this was shown to be due to inhibition by H 2 O, which is a primary product of the NOH 2 reaction. The product distribution from competitive experiments with mixtures of CO and H 2 , shows that H 2 reacts preferentially to CO, over iron oxide. The water-gas shift reaction occurs more readily over iron oxide than chromium oxide and the H 2 formed reduces NO to NH 3 . The produet distribution from the NOH 2 reaction differs with the two catalysts. Over iron oxide the major product is NH 3 , while with chromium oxide it is N 2 . Since chromium oxide neither decomposes NH 3 nor promotes the NONH 3 reaction with any greater ease than Fe 2 O 3 , it is concluded that the reduction of NO with H 2 occurs by different mechanisms over the two catalysts.