Co-Exchanged IM5, a Stable Zeolite for the Selective Catalytic Reduction of NO in the Presence of Water and SO₂

IM5 is a recently discovered zeolite that presents a high hydrothermal stability and, when exchanged with cobalt, shows a high activity for the selective catalytic reduction of NO with propane. The catalytic behavior of a cobalt-exchanged IM5 zeolite is compared with that of a cobalt-exchanged ZSM5 zeolite. The state of the cobalt in the zeolite and the influence of the partial pressure of oxygen, reaction temperature, and the presence of water and SO2 are studied. It is shown that cobalt is mainly as Co2+ in a tetrahedral environment, although the presence of a small amount of other cobalt states cannot be rejected. The material is very active for the selective catalytic reduction of NOx with propane at 723 K and, what is important, with a high oxygen concentration. The presence of possible catalyst poisons such as SO2 and water does not result in a deactivation of the Co−IM5.