The application of cationic layered clays as DeNOx catalysts with both ammonia or hydrocarbons as reducing agents was discussed. Several preparation procedures: acidic treatment, pillaring, introduction of active material or carbon deposits were described and the influence of these procedures on catalytic activity in SCR deNOx reaction were discussed. The conclusions about possible mechanisms are drawn on the basis of the data obtained. A special attention was paid to the role of acidic and redox sites. The effect of poisoning molecules (SO2 and H2O) on catalytic activity and selectivity was considered. (c) 2006 Elsevier B.V. All rights reserved.