The three-way catalysts currently used for controlling NO x gaseous pollutants from IC engines cannot be used under lean conditions such as diesel engine exhausts. Approaches to NO x reduction have therefore focused on direct decomposition of NO to its elements or selective catalytic reduction with hydrocarbons to N 2 . Metal-doped ZSM-5 catalysts are active in these reactions, with Cu-ZSM-5 receiving most attention. A survey of the literature regarding the performance, reaction mechanism and durability of these catalysts under engine conditions is presented. Although copper-based ZSM-5 has adequate catalytic properties, there remain doubts about its ability to withstand diesel exhaust conditions, since they deactivate at high temperature, due to dealumination or/and Cu migration.