The three-way catalysts currently used for controlling NOx gaseous pollutants from IC engines cannot be used under lean conditions such as diesel engine exhausts. Approaches to NOx 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.